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please
2009-Jul-23, 08:34 AM
I have noticed in this thread (http://www.bautforum.com/against-mainstream/90895-faster-then-light-quantum-communication-possible-2.html) that people were dismissing physical possibility of faster-than-light information transmission on grounds that it would violate causality (roughly, cause must precede effects in all possible frames of reference). I have seen people discussing spinning wormholes in GR and how does that violate causality, and noone cared; here, howeveer, a guy tries to discuss entanglement, and his argument is dismissed because of causality

So I asked, among other things, is caulaity not a mere extrapolation of our limited human experience upon everything in the whole universe, and the response was "You can't die from being shot by a bullet - before that bullet was fired" (ironic, isn't it).

Leaving aside countless but little-relevant examples of how such an extrapolation of our experience failed in the past, why is causality so uber important? I mean doesnt all the math in physics just work both ways (although maybe differently) regardless of causality?

pzkpfw
2009-Jul-23, 09:11 AM
Some background reading:

http://en.wikipedia.org/wiki/Arrow_of_time

http://en.wikipedia.org/wiki/Causality_(physics)

please
2009-Jul-23, 09:32 AM
You forgot

http://en.wikipedia.org/wiki/Retrocausality

please
2009-Jul-23, 09:35 AM
I guess what I mean here is, sure thing, causality is not violated every day, or else the concept would not even exist :D but, what makes us think that causality could not be violated in any form or at any scale at all?

undidly
2009-Jul-23, 12:32 PM
There is never ever any violation of causality.
It may look that way from some frames but is not real.
The question is why do some people think that FTL comunications violates causality.The information just gets there sooner.

Send a message FTL to 1 light year away,receive a reply also FTL after 1 second.
That is 1 second AFTER it is sent.

I know light or radio cannot go that fast but maybe something can.

I think we all agree that objects or particles with mass cannot even get to
the speed of light in a vacuum.

Some say that FTL is impossible because such would violate causality.
It does not violate causality so IS possible.

please
2009-Jul-23, 12:47 PM
undidly, you thread hijacker! now people are bound to come and argue you to death with their lorenz transforms to prove you wrong, and noone will answer my original question :)

Ken G
2009-Jul-23, 02:07 PM
I guess what I mean here is, sure thing, causality is not violated every day, or else the concept would not even exist :D but, what makes us think that causality could not be violated in any form or at any scale at all?You are certainly correct that all "laws" of physics are conditional upon our current understanding of things. But it is fairly uncontroversial that we have levels of reliability of laws, which with some reflection I might characterize as follows, in order of increasing confidence in the laws (though the distinctions are not set in stone):
1) "effective" laws-- these are relations that we know from the start are incorrect, they are approximations built purely to give the right answer in certain situations, but they are not based on any generalized principles and their domain of applicability is limited to what has already been shown to work out.
2) invented laws-- these are laws in which a physicist invents some concept, like the force of gravity, and derives the properties it would need to exhibit the behavior it does. These are relied upon based on their general plausibility and success against testing, so are expected to generalize fairly well, but we are not shocked when we discover there are limits to their applicability (consider the force of gravity).
3) symmetry/conservation laws-- these are laws which are based on some fundamental symmetry, which by Noether's theorem connects them to conserved quantities. These are also conditional, like #2, but have a higher status because they are not based on the "invention" of arbitrary entities like certain forces, they are based on some fundamental structure of nature, like a symmetry. Symmetries were pretty much made to be broken, so these are also conditional, but they are rarely broken and seemingly only in extreme situations.
4) consistency laws-- these are laws that, were they not true, reality could lead to logical contradictions (like people keeping their own mothers and fathers from meeting). Logic is just another invention of our intelligence, so we don't know it always works, just as we don't even know that arithmetic proofs always have to be consistent, but no counterexamples are known. It would be the most serious crack in the foundation of our intelligence if logical inconsistencies emerged in the structure of the universe itself. But yes, this does not make it impossible, it just means it is our "last resort", we don't do it any way but kicking and screaming.

Now, a causal loop like A causes B causes C causes A is not a logical inconsistency because there are no contradictions involved, it's just a bit bizarre. So it's not clear that causality is of type #4, some violations of it would only be a violation of a "level 3" princple. But still, even those we don't build in to our theories until we have to. That's not the same as saying "your iidea must be wrong", it's more like "I have no particular reason to accept that proposition, as rejecting it is more consistent with our current understanding."

There is another issue also, which differentiates spinning wormholes from entanglement. The situation involved in entanglement is accessible to experiment, and experiments have demonstrated that our current quantum mechanical understanding of entanglement works swimmingly. Quantum mechanics preserves causality, if one uses a careful description of what information means. That is, when quantum mechanics is built to respect relativity, it predicts that information cannot be communicated via entanglement in any kind of spooky way, and the experiments appear to bear this out. There's no reason to expect causality to break down in entanglement any more than in any other physical scenario. Of course, there's also no reason to expect GR to break causality, it's just that people can talk about it with less concern that their statements will ever need to be confronted with observations.

grant hutchison
2009-Jul-23, 02:44 PM
There is never ever any violation of causality.
It may look that way from some frames but is not real.
The question is why do some people think that FTL comunications violates causality.The information just gets there sooner.It's more complicated than that. As soon as FTL communication occurs, there are some reference frames in which the information really, truly arrives before it was sent.
I've no wish to hijack please's thread, so I'll refer you to the extensive discussion on the Why does FTL not work? (http://www.bautforum.com/space-astronomy-questions-answers/64167-why-does-ftl-not-work.html) thread.

Grant Hutchison

Ken G
2009-Jul-23, 02:58 PM
And without hijacking this thread on causality, I can point out the salient issues of that discussion.

Basically, relativity recognizes only a general type of time-ordering wherein events A and B exhibit one out of three possible causal connetions: A can cause B, B can cause A, or neither A nor B can cause the other. (We could generalize "cause" to just mean "cause it to come out differently than it would have otherwise." It is connected to the concept of determinism, whose limitations are certainly cracks in the whole basis of causality.) A key result of relativity is that those three connections are all we can say in an objective and invariant way, they hold for all observers, they are "part of the reality". When we restrict to events on our own "world line" (the path we take through spacetime, so these events are "what happens" to us), if we associate event B with "now", then "A can cause B" puts A in our past, "B can cause A" puts A in our future, and the "neither" possibility is collapsed into just a boundary where B and A are both the instantaneous present. I feel that a key mistake in the conceptualization of special relativity is to extrapolate nonlocally (i.e., to places not on our world line, so to events that did not "happen to us") this "boundary" into a nonexistent concept of "simultaneity". But in fact there is no demonstrable concept of simultaneity, there is only the three possibilities above. So special relativity's reliance on a "simultaneity convention" is ontologically bogus-- a flaw corrected in general relativity (by Einstein himself, guided very much by such ontological thinking, for you philosophy-haters, you know who you are).

The way this all relates to FTL is that FTL observers would break the invariance of those three causal classes. However, this only says that observers cannot move FTL with respect to each other, it says nothing about particles (ergo speculations about tachyons, and the well known excesses permitted by the uncertainty principle-- indeed Feynman path integrals routinely include particles moving backward in time, and I'm pretty sure this is important to the action of virtual particles, though I don't actually so such calcuations so I cannot say more).

There is a second restriction on FTL, which is that information cannot go FTL, because if it did, an observer could receive a message before that same observer sent out that same message (assuming certain symmetries in regard to the propagation of that information). That is contradictory when one brings in issues like the free will of the observer, an area that modern physics is ill-equipped to address so it remains unclear if such closed timelike causality loops are really contradictions or not. (Some of this did not come up in that other thread, but I don't mean to re-open it here!)

please
2009-Jul-23, 03:07 PM
@KenG,

At part 1 of your last reply, is what "relativity recognizes" not entirely up to our definitions of worldlines? I mean, in that thread, it is said that by insta-jumping in frame A you are time-traveling in frame B but so what, it is not something inexpressible in terms of relativity (as these posts itself demonstrate).

At part 2, you have really compressed your thought to the point where I couldnt see what do you have against "simultaneity" - it is perfectly valid concept as long as we stick to just one frame.

Ken G
2009-Jul-23, 03:26 PM
At part 1 of your last reply, is what "relativity recognizes" not entirely up to our definitions of worldlines? I mean, in that thread, it is said that by insta-jumping in frame A you are time-traveling in frame B but so what, it is not something inexpressible in terms of relativity (as these posts itself demonstrate).I'm not quite sure what you are asking. Relativity is a theory, so it defines its primitive constructs and how to manipulate them. Given these definitions and rules, it makes predictions that are extremely successful. It also rests on certain general ontological principles that seem to achieve great simplicity and parsimony. As such, we accept it as "our best current understanding." "Insta-jumping" in some frame can certainly be expressed in the coordinates being used, the contradiction is in the ramifications of that jumping, which are problematic.


At part 2, you have really compressed your thought to the point where I couldnt see what do you have against "simultaneity" - it is perfectly valid concept as long as we stick to just one frame.My problem with it is that it is sheer coordinatization-- there is no sense to which reality exhibits this concept in any demonstrable way. Hence, our scientific ontology should not either. It's not that it's wrong, it's that it is unnecessary, and that's all I meant by "bogus."

please
2009-Jul-23, 03:36 PM
to 1, I mean, Einstein postulates lead us to Minkowski space, but they do not dictate that worldlines must not have gaps (except those for inert observers and light). Of course, you could say that by allowing worldlines to have gaps we would change what is now known as SRT so we should not call that relativity, but that would be kinda weak argument :)

to 2, same way you could dismiss a notion of things being at the same place.

Argos
2009-Jul-23, 03:36 PM
if we associate event B with "now", then "A can cause B" puts A in our past, "B can cause A" puts A in our future, and the "neither" possibility is collapsed into just a boundary where B and A are both the instantaneous present.

I think one of the problems in understanding causality is that one is used to thinking of a "frame" only in spatial terms, when in fact, we have to keep in mind that we have a position in time, in the context of relativity.

TonyE
2009-Jul-23, 03:59 PM
Some thoughts::whistle:

Causality is a subjective human concept. We are used to seeing B happen after A so we say A causes B and that B is caused by A.

At the subatomic level individual interactions are generally time reversible and their outcomes based on probablilities. But everything we normally perceive consistes of complex groups of interactions and during those interactions the overall probabilities are that entropy will increase.

As our brains, and hence our streams of consciousness, involve complex sets of physical interactions so they will also proceed in the direction of low-to-high entropy. So our stream of consciousness proceeds - probabalistically - in the same direction as all complex interactions. In other words we perceive the arrow of time to go in the direction it does because thats the direction our brains are working.

So causality is subjective and not a feature of physical reality. So there is no 'law' against breaking causality ony a VERY high probability that WE will never observe a complex interaction going 'the wrong way'.

Ken G
2009-Jul-23, 04:10 PM
to 1, I mean, Einstein postulates lead us to Minkowski space, but they do not dictate that worldlines must not have gaps (except those for inert observers and light).We have more than just the geometry of spacetime, we have also (Newton's laws) a theory of dynamics within that geometry. It is the latter which precludes such "gaps". By "precludes", I mean "would be inconsistent with the theory", not "can't happen". The success of the theory exemplifies the fact that such gaps are not observed to happen.

to 2, same way you could dismiss a notion of things being at the same place.You mean the same place at different times? If so, yes, that is also pure arbitrary coordinatization.

please
2009-Jul-23, 04:11 PM
to echo TonyE somewhat, I have my doubts about related so-called paradoxes such as killing yourself in past (or your grandfather, or stepping on a butterfly), I mean they are always formulated in terms of small number of events, but exact connection between those events is omitted; our brain that struggles to find this connection, and when it fails, declares it a "paradox". I'm sure if authors of these paradoxes would present us complete Feynman-style diagram instead, with all the worldlines connecting the events, we wouldn't really find that diagram paradoxal (just like in the case of closed loops through wormholes).

Ken G
2009-Jul-23, 04:12 PM
I think one of the problems in understanding causality is that one is used to thinking of a "frame" only in spatial terms, when in fact, we have to keep in mind that we have a position in time, in the context of relativity.I don't know if this is what you are alluding to, but in my view, a "frame" is a world line, so extends globally only in time, but not in space. It is all you can associate with a particular observer, so that seems fully consistent with the concept of a frame.

Ken G
2009-Jul-23, 04:18 PM
As our brains, and hence our streams of consciousness, involve complex sets of physical interactions so they will also proceed in the direction of low-to-high entropy. So our stream of consciousness proceeds - probabalistically - in the same direction as all complex interactions. In other words we perceive the arrow of time to go in the direction it does because thats the direction our brains are working.
Yes, I have come to simiilar conclusions, and I think this is a valid view that is held by many.


So causality is subjective and not a feature of physical reality. If by "subjective" you mean "created by our intelligence", then all "features of physical reality" that are expressible in language share that attribute. If by that word you mean "depends on the observer", then the whole point of relativity is that this is not observed to be the case-- causal relationships are invariant to the observers. That's where the ontological status of a "cause" derives, not the other way around.
So there is no 'law' against breaking causality ony a VERY high probability that WE will never observe a complex interaction going 'the wrong way'.But you are describing a law there. For example, the second law of thermodynamics. It is true that "laws were made to be broken", but that doesn't mean they aren't laws. But it is true that the notion of causality is connected to the notion of determinism, and there are certainly cracks in that concept. In a sense you are saying that causality is an emergent property of reality, moreso than a fundamental property, but then, everything we call fundamental is probably emergent too.

Argos
2009-Jul-23, 07:00 PM
I don't know if this is what you are alluding to, but in my view, a "frame" is a world line, so extends globally only in time, but not in space.

Well, I was thinking of spacetime coordinates. People tend to forget the 'time' component. But yeah, I think I agree with you.

DrRocket
2009-Jul-23, 07:22 PM
There is never ever any violation of causality.
It may look that way from some frames but is not real.
The question is why do some people think that FTL comunications violates causality.The information just gets there sooner.

Send a message FTL to 1 light year away,receive a reply also FTL after 1 second.
That is 1 second AFTER it is sent.

I know light or radio cannot go that fast but maybe something can.

I think we all agree that objects or particles with mass cannot even get to
the speed of light in a vacuum.

Some say that FTL is impossible because such would violate causality.
It does not violate causality so IS possible.

The reason that FTL commuication is thought to violate causality, is because it does.

If you look at the derivation of the Lorentz transformation in special relativity, you will find that if you assume causality, then it is impossible to transmit a signal superluminally. See for instance pages 35, 36 in Essential Relativity, Special, General and Cosmological by Wolfgang Rindler.

What is shown there is that if you permit superluminal informatoin transfer then there will be reference frames that disagree on the order of events. The speed limit of "c" provides for invariance of causality.

DrRocket
2009-Jul-23, 07:31 PM
I have noticed in this thread (http://www.bautforum.com/against-mainstream/90895-faster-then-light-quantum-communication-possible-2.html) that people were dismissing physical possibility of faster-than-light information transmission on grounds that it would violate causality (roughly, cause must precede effects in all possible frames of reference). I have seen people discussing spinning wormholes in GR and how does that violate causality, and noone cared; here, howeveer, a guy tries to discuss entanglement, and his argument is dismissed because of causality

So I asked, among other things, is caulaity not a mere extrapolation of our limited human experience upon everything in the whole universe, and the response was "You can't die from being shot by a bullet - before that bullet was fired" (ironic, isn't it).

Leaving aside countless but little-relevant examples of how such an extrapolation of our experience failed in the past, why is causality so uber important? I mean doesnt all the math in physics just work both ways (although maybe differently) regardless of causality?

The math in the physics does not work both ways. Although equations are generally time-symmetric in that you can run time backwards and detrermine the past from the present, the orderiing of events is still the same for all observers. All observers agree on what is the past and what is the present. That is what causality is all about.

If you accept non-causality in special relativity, you will have observers that do not agree on the order of events. Some will say that you died after the bullet was fired and some will say you died before. That sort of thing would make the very notion of cause and effect in physical laws invalid, and causality is what physics is all about.

Ken G
2009-Jul-23, 07:51 PM
All observers agree on what is the past and what is the present. That is what causality is all about. Just to clarify, what is meant by "the present" here is not the concept of "simultaneity", it is the concept of "a set of events that can have no causal connection to each other." "Now" is an arbitrary concept when applied off of our own world line, but this general class of "present-like" events is an invariant categorization, more commonly termed "spacelike separated."


If you accept non-causality in special relativity, you will have observers that do not agree on the order of events. Some will say that you died after the bullet was fired and some will say you died before. That sort of thing would make the very notion of cause and effect in physical laws invalid, and causality is what physics is all about.I suspect there are ways to generalize the concept of causation to account for closed timelike loops like A --> B --> C --> A. In the absence of higher beings with awareness and free will, for example, such a setup creates no fundamental contradiction, and all the causal relations can be pairwise meaningful. Ergo, the causality requirement of which you speak has a purely philosophical, albeit seemingly reasonable, character. Not that you personally would trust philosophers to ponder the point, but there you have it.

By the way, I have no idea what is the "order of Kilopi."
ETA: apropos of nothing, I now surmise it comes when you have more than 1000 X pi posts. Has this been true for a long time and I've not noticed?

grant hutchison
2009-Jul-23, 08:11 PM
By the way, I have no idea what is the "order of Kilopi."
ETA: apropos of nothing, I now surmise it comes when you have more than 1000 X pi posts. Has this been true for a long time and I've not noticed?The kilopi concept has rather a long history at BAUT. The "Order of Kilopi" arrived quite recently. :)

Grant Hutchison

Ken G
2009-Jul-23, 08:17 PM
The kilopi concept has rather a long history at BAUT. Ah. I notice there is also an asteroid named "3142 Kilopi", which may be where the idea originates.

Van Rijn
2009-Jul-23, 08:26 PM
Send a message FTL to 1 light year away,receive a reply also FTL after 1 second.
That is 1 second AFTER it is sent.


As you've done in other threads, you're assuming an absolute reference frame. This is not compatible with SR (http://en.wikipedia.org/wiki/Special_relativity#Lack_of_an_absolute_reference_f rame).

pzkpfw
2009-Jul-23, 08:58 PM
undidly, please don't put your ATM replies into a thread in Q&A.

Your idea has been discussed (and dismissed) before.

This is a warning of suspensions if you do that again.

Thanks

robross
2009-Jul-23, 10:20 PM
Depending on how deep you want to go into the analysis, "causality" is really a philosophical concept.

There's no way to *prove* causality exists. It's an observation, a postulate, a conjecture, a conclusion, etc.

Now, perhaps if there were a creator and he could explain to us that indeed causality is a Law of nature, (and we accepted his credentials and explanation), then we could know that causality is a universal truth of reality.

But since we can't have that level of certainty, we just assume it's true, like we assume the cosmological principle, otherwise we would have no framework upon which to build our physical laws.

Rob

Cougar
2009-Jul-24, 12:45 AM
Logic is just another invention of our intelligence, so we don't know it always works... but no counterexamples are known.

Whoo boy, Ken, you are strict! :) Yes, it certainly takes an intelligence to notice that certain logical connections can be relied upon. But I'm thinking logic isn't being invented by the intelligence, so much as being noticed by it.

Cougar
2009-Jul-24, 01:07 AM
...it is not something inexpressible in terms of relativity...



"Einstein's equations do not specify the universe; rather they may be considered a general framework within which you can construct many different model universes." - Tony Rothman

On the other hand, most scientists are interested in models that are verifiable and testable in this universe. In other words, models that do not contradict what is observed.

It's not good enough that you can just "express" something by changing some parameters of the equation. The result has to "make sense" and be consistent with observation. The simplest example is "18 divided by zero." It's expressible, but undefined and, dare I say, essentially meaningless?

DrRocket
2009-Jul-24, 01:07 AM
Ju

By the way, I have no idea what is the "order of Kilopi."
ETA: apropos of nothing, I now surmise it comes when you have more than 1000 X pi posts. Has this been true for a long time and I've not noticed?

There is a thread (http://www.bautforum.com/forum-introductions-feedback/90740-new-user-rankings-discussion.html) discussing this, and your supposition is apparently correct.

However, I wonder a bit at the selection of the designation that replaced "senior member" since 1000 x pi is quite irrational.

DrRocket
2009-Jul-24, 01:17 AM
I suspect there are ways to generalize the concept of causation to account for closed timelike loops like A --> B --> C --> A. In the absence of higher beings with awareness and free will, for example, such a setup creates no fundamental contradiction, and all the causal relations can be pairwise meaningful. Ergo, the causality requirement of which you speak has a purely philosophical, albeit seemingly reasonable, character. Not that you personally would trust philosophers to ponder the point, but there you have it.



I wold most certainly trust philosophers to ponder that point or any point. Ponder is what they do best, and ad infinitum. I would not expect a conclusion, however.

If you have evidence of any closed timelike loops consistent with general relativity than would be quite a discovery.

Current physics, however has problems with your closed timelike loop since it implies both
A---->B---->C and B---->C---->A hence both A---->B and B---->A (Edited to correct last ordering)
which is a serious problem.

Without causality the notion of predictability of events goes out the window, since you now have the potential to invert cause and effect. Not only invert them, but have the order be dependent on reference frame. If the order of events is not invariant, then I think you have rather a problem with ALL of physics.

publius
2009-Jul-24, 02:22 AM
However, I wonder a bit at the selection of the designation that replaced "senior member" since 1000 x pi is quite irrational.

However, it also transcendental. The square root of two is merely irrational. Us pi-ers are in a transcendent realm.


-Richard

publius
2009-Jul-24, 02:33 AM
You know, that's the best way to put this. FTL in Minkowski allows the equivalent of a closed time-like curve.

There are such closed time-like solutions in GR. See the Godel metric for an example. And the region between event horizons in the Kerr metric also allows closed time like curves (but such an obscenity is causally disconnected from the outside universe by the outer horizon).

No one really thinks these things are physically possible. A thorny question is what happens if matter itself tries to follow such a closed time-like curve. GR becomes indeterminate then. The Kerr metric is a simplfied idealization and it is believed but no yet proven to my knowledge that any real matter in a rotating collapse would not allow the true Kerr interior to form. It is proven the Kerr interior is highly unstable to slight pertubations from infalling mass-energy. Then's there's something about Cauchy horizons (associated with closed time-like curve boundaries) and infinite frequency boosts.

A causal loop (A --> B --> A), while obscene, is consistent. What is the show stopper is A --> B --> not A. That is insane, and there just aren't any deterministic solutions possible then. Trouble is, if you can have one, you can have the other.

-Richard

George
2009-Jul-24, 02:44 AM
There is a thread (http://www.bautforum.com/forum-introductions-feedback/90740-new-user-rankings-discussion.html) discussing this, and your supposition is apparently correct. Ah, I was wondering about this.

I would bet there's more causality at hand to the D.O.K. level than a mere numerical count. [One need only reverse a mirrored image to see the Shadow of which I speak. ;) ]

Ken G
2009-Jul-24, 02:59 AM
Yes, it certainly takes an intelligence to notice that certain logical connections can be relied upon. But I'm thinking logic isn't being invented by the intelligence, so much as being noticed by it.This is a profound issue. I can think of at least three stances:
1) logic is dreamed up by intelligence, and amazingly, we find it works for many things in carefully controlled situations,
2) logic is embedded in reality, and we discover that because we are intelligent,
3) intelligence is the ability to use logic, like hearing is the ability to detect sound, and each has its uses in the real world.
I'm sure other models could be adopted as well. Which is best? Bring on the tests. Perhaps each has its own advantages in various contexts.

Ken G
2009-Jul-24, 03:26 AM
If you have evidence of any closed timelike loops consistent with general relativity than would be quite a discovery.
Others have beaten me to it.

Without causality the notion of predictability of events goes out the window, since you now have the potential to invert cause and effect. Actually, A --> B --> C --> A is not inconsistent, as publius points out. It also does no violence to predictability, because when you have A, you can predict B, and so forth. Prediction is not a global relation, it is a local one, as expressed in the fact that all equations of physics are differential equations set up subject to boundary conditions that are outside the laws themselves.
If the order of events is not invariant, then I think you have rather a problem with ALL of physics.A loop does have an order, but the order is a local relation, not a global one. This is certainly weird, but not outside the fundamental spirit of any of the laws of physics for simple enough systems. Indeed, Bohr used a very similar type of situation to understand the quantization of the hydrogen atom.

DrRocket
2009-Jul-24, 03:32 AM
However, it also transcendental. The square root of two is merely irrational. Us pi-ers are in a transcendent realm.


-Richard

Irrationally transcendent then ?

Not (at) the root of any rational polynomial. Not in an algebraic extension field of the rationals.

I though that went out in the 60's with the renewal of Hait Ashberry.

Do you guys wear paisley shirts ?

Ken G
2009-Jul-24, 03:46 AM
No one really thinks these things are physically possible. Perhaps on macro scales they lead to the same kinds of paradoxes as Schrodinger's cat, but on micro scales there's far less trouble. Imagine a universe with nothing in it but one simple harmonic oscillator. In the spirit of not including anything that is not needed, time in such a universe would be "modded out" by the period of the oscillator. Thus it would be a universe with A-->B-->A type processes up the wazoo, yet still obey all the laws as we know them now. Indeed, as I pointed out to DrRocket, that's very much the spirit of the Bohr atom.

I think the ontological issue is, does time exist in the universe before we put matter in it, or is time about what the matter is capable of doing? I think the spirit of relativity is very much the latter, and time has an even more ambiguous relationship with quantum mechanics. Causality in quantum mechanics is an emergent property, not a fundamental one, and the rules of that emergence might preclude macroscopic closed timelike curves-- but not microscopic ones. That's also in the spirit of relativity, to make space and time follow dynamical (emergent) rules, not just the matter in them.


A thorny question is what happens if matter itself tries to follow such a closed time-like curve. GR becomes indeterminate then. That's certainly unpleasant on macro scales, but micro scales may have far less trouble with it. In the spirit of Feynman path integrals, determinism is an emergent property of a sum over many indeterminate contributors. I suspect such sums would simply yield periodic phenomena in closed timelike curves, a la Bohr again.


A causal loop (A --> B --> A), while obscene, is consistent. What is the show stopper is A --> B --> not A.Excellent point.

That is insane, and there just aren't any deterministic solutions possible then. Trouble is, if you can have one, you can have the other.
Not necessarily-- some kind of "sum over consistent histories" might come into play to assure that B could not lead to ~A if A was in B's history. It would certainly be weird for A --> B --> A, but not inconsistent with the structure of the basic laws, just inconsistent with how those laws have to work out for our routine observations.

DrRocket
2009-Jul-24, 03:54 AM
You know, that's the best way to put this. FTL in Minkowski allows the equivalent of a closed time-like curve.
-Richard

How ?

In fact, how do you get FTL in Minkowski at all ?

Are you allowing nonorthochronous elements in the Lorentz group ? If so your group of symmetries is going to be rather unsavory. Disconnected I think.

DrRocket
2009-Jul-24, 04:03 AM
Perhaps on macro scales they lead to the same kinds of paradoxes as Schrodinger's cat, but on micro scales there's far less trouble. Imagine a universe with nothing in it but one simple harmonic oscillator. In the spirit of not including anything that is not needed, time in such a universe would be "modded out" by the period of the oscillator. Thus it would be a universe with A-->B-->A type processes up the wazoo, yet still obey all the laws as we know them now. Indeed, as I pointed out to DrRocket, that's very much the spirit of the Bohr atom.

Whoa hoss.

You don't do away with causality by simply invoking periodic phenomena. You also can't get away with simple quantum mechanics and a one-atom universe.

QM, unlike QFT cannot handle particle decay or any changes in numbers of particles.

If you are going to try to make this argument you will have to be a lot more precise.


Causality in quantum mechanics is an emergent property, not a fundamental one, and the rules of that emergence might preclude macroscopic closed timelike curves-- but not microscopic ones. That's also in the spirit of relativity, to make space and time follow dynamical (emergent) rules, not just the matter in them..

You need to be more precise here as well. Causality in QM is a bit tought to talk about because of the stochastic aspect. But the evolution of the quantum state is totally deterministic, and I think also that the equations would be termed causal.

In fact, if we are going to invoke quantum mechanics and random phenomena, then I think we need a clear definition of what "causal" means.

publius
2009-Jul-24, 04:11 AM
How ?

In fact, how do you get FTL in Minkowski at all ?



You just allow "information" to follow a space-like path and ponder the consequences. That is, we don't imagine normal matter actually following such a non-time-like path, we just imagine that somehow information or some exotic FTL whatsit can be transmitted along such a path and see where that leads.

In Minkowksi, every FTL path (some slope greater than c) is the spatial axis of some time-like frame, by the relation u*v = c^2, where v is the velocity of the time-like path, and u is the slope of that frame's spatial axis. For example, if you're moving at c/2, you're spatial axis has a slope of 2c to me.

So if something moves at 2c to me, it's moving instantaneously to you. If faster, it's moving backwards in time to you. Now, when you carefully parameterize that by some 's' (which would be proper time for a time-like path).

We can construct a scenario where I shoot information along my instantaneous path (or above the speed to get the backwards in time looking behavior) to you in relative motion and you shoot it back to me along *your* spatial axis, and that intersects my world line before I sent the original information, forming the functional equivalent of a closed-time curve.

-Richard

publius
2009-Jul-24, 04:26 AM
And finally (we went over this in some detail way back in some old thread about this), we can imagine saying, well, let's don't fret about some paths appearing to move backwards in time for some observers, let's just forbid those closed temporal loops.

If we do that, we find we've singled out a special frame. In that special frame, all possible paths will be restricted to 0 < v < infinity, and nothing moves backwards in time (which can be thought as a speed "faster" than instantaneous". Other frames will see some of those paths moving backwards in time, but they can immediately find the one frame where that never happens and thus know their state of absolute motion with respect to this one true frame. And that's the frame where everything runs foward in time as normal.

-Richard

DrRocket
2009-Jul-24, 04:59 AM
You just allow "information" to follow a space-like path and ponder the consequences. That is, we don't imagine normal matter actually following such a non-time-like path, we just imagine that somehow information or some exotic FTL whatsit can be transmitted along such a path and see where that leads.


-Richard

OK you can do that. But that has nothing to do with Minkowski. All that you are really saying is that Minkowski is just 4-space with some non-degenerate metric. So forget the metric and just connect two points with a line, or a curve. The fact that it is not time-like we just ignore. There is no distinguished class of vectors or curves and we are simply ignoring the natural geometry imposed by the Minkowski metric. Or, if you don't allow simply going back along the time axis, or similar things, you are basically back in the Newtonian case where there is no speed limit and the symmetry group is the Galilean group.

I think that when you "ponder the consequences" in this case you may find that they are unacceptable from a physical perspective.

You can do the same thing in GR, just as easily. The manifold is connected, so you can join any two points with a curve. That curve won't necessarily be a geodesic. God only knows what the significance of such a thing is. I presume, however, that your example using the Kerr metric, does involve geodesics. That is a bit more interesting.

Ken G
2009-Jul-24, 05:02 AM
You don't do away with causality by simply invoking periodic phenomena. You also can't get away with simple quantum mechanics and a one-atom universe.
All laws of physics are idealizations, so none can be criticized on the grounds that they are being idealized. Perfectly periodic systems are allowing in the laws of physics that we now have, indeed they are invoked routinely. Impossible to actualize of course, but we are talking about the laws here.

To work in the laws of physics, causality must be applicable to a perfectly periodic system, like a particle bouncing around inside a perfectly elastic one-dimensional container. The causality in such a system is cyclic, it just is. A wall causes a particle to bounce, that's pretty clearly a cause. If the system is truly periodic, time is modded out by the bounce period, and A causes B causes A, without contradiction or even awkwardness. It's a highly idealized system, to be sure, and could not be embedded in larger structures without breaking the perfectly cyclic character. Nevertheless, the laws have to work on all systems, even very simple ones, if we are going to call them laws.



QM, unlike QFT cannot handle particle decay or any changes in numbers of particles.Many simple systems exhibit neither. Again, it is not physics to say "but the universe isn't really like that". There is no physics that escapes that issue, the very first thing physics is is replacing the universe with something simpler.

Causality in QM is a bit tought to talk about because of the stochastic aspect. Correct, that's why I said causality in QM is an emergent property, something that appears after the path integrals are carried out, not in the path integrals themselves.



But the evolution of the quantum state is totally deterministic, and I think also that the equations would be termed causal.And perfectly cyclic, in many cases.


In fact, if we are going to invoke quantum mechanics and random phenomena, then I think we need a clear definition of what "causal" means.We'd need that in Newtonian physics too, and those systems can be perfectly cyclic as well. My reference to macro systems in GR had to do with the problem of taking a system that is not perfectly cyclic, and trying to get it to be perfectly cyclic by ramming it through a closed timelike curve. I speculated that some principle, like summing over consistent histories, would impose the necessary cyclic character on the macro system, sort of a macro analog of a Bohr atom. My bringing in quantum mechanics was merely to show that we got that surprise once already.

Causality in QM is a bit tricky, indeed. In entanglement, it gets massacred by people who are not applying a consistent concept of what causality must mean. You hear language like measuring the spin of one particle causes the spin of another particle to be something, which would violate relativity. It is possible that a workable definition of causality in quantum mechanics is still lacking, I really don't know. If so, then this may be a useful path to take toward unification. You'd love it, as it is using a philosophical concept to guide physics.

DrRocket
2009-Jul-24, 05:27 AM
All laws of physics are idealizations, so none can be criticized on the grounds that they are being idealized. Perfectly periodic systems are allowing in the laws of physics that we now have, indeed they are invoked routinely. Impossible to actualize of course, but we are talking about the laws here.



Perfectly periodic systems are not the problem. Perfectly periodic systems are just fine.

It is the basic laws that govern those systems that contain the causality. Being periodic does not violate causality. And you don't get to "mod out" time just because a system is periodic.

What you are doing to get around causality is not postulating a perfectly system but rather a perfedctly periodic universe, universe that consists of only a single harmonic oscillator. That is an entirely different kettle of fish.

Your point is absolutely correct. We are talking about the laws. And while you might be able to "mod out time" in a perfectly periodic universe, you cannot do so in our universe, even with a perfectly periodic system. That set of "modded out laws" will not apply to our universe at large.

Just to make things a bit simpler, consider a universe with just two simple harmonic oscillators. Oscillators with incommensurate periods. Now you cannot play your game of "modding out" time, but the physics ought not be all that different, particularly if the oscillators do not interact. You are either stuck with the usual version of time, or you have two break the universe into two pieces, each with a different version of time.

You are playing the game of the "lanscape" string physicists and looking at alternate universes with alternate laws, based only on the mathematics that governs the consistency of those laws and placing some sort of reality on them. That is not justified. It may be an interesting gedanken experiment, but there are limits to its applicability.

Ken G
2009-Jul-24, 07:08 AM
Being periodic does not violate causality. I never said it did-- indeed, I said the opposite, that our notions of causality must embrace perfectly periodic systems so that we not make claims on causality that are insufficiently general.

And you don't get to "mod out" time just because a system is periodic.
Actually, you do. This is the full meaning of an equivalence class.



What you are doing to get around causality is not postulating a perfectly system but rather a perfedctly periodic universe, universe that consists of only a single harmonic oscillator. That is an entirely different kettle of fish.
As I said, it is a standard device in deriving laws of physics to consider such simplified systems as though they were microcosms. Indeed, I know of no other situations in which laws are derived.

That set of "modded out laws" will not apply to our universe at large.As I said, this is not a valid criticism of any law of physics, as there are no known laws that survive it. Symmetries are broken, principles are violated, willy nilly. Not a one of them is meant to be anything but an idealization, applying to idealized systems that are never the universe "at large". Even the cosmological principle, the sole inherently "at large" principle in all of physics, is really nothing but a useful idealization.


Just to make things a bit simpler, consider a universe with just two simple harmonic oscillators. Oscillators with incommensurate periods. You're not getting it. When the energy levels of a hydrogen atom are calculated, it is done as though the atom is alone in the universe. No one says "that's an invalid calculation, because I can imagine a universe with two atoms in it." We put in a second atom when we want to explore different kinds of interactions, and the laws that relate to them. It's the choice of the physicist exploring the laws, we are never required to put the whole universe into every law! That has simply never been the way physics is done.

Consider for example the second law of thermodynamics, that entropy increases in the spontaneous evolution of large closed systems. I could try to define a concept of entropy for a system of five particles, but there'd be no advantage, because the law wouldn't apply there. We would not then say "you can't talk about a universe of five particles because the real universe has more than that", we just say "the second law of thermodynamics doesn't apply to five particles." It's about understanding the limitations of our laws, and their proper realm of applicability. I'm saying causality has similar limitations, and we should not make blindly broad claims like you can't have a closed timelike loop because it violates causality.


Now you cannot play your game of "modding out" time, but the physics ought not be all that different, particularly if the oscillators do not interact. You are either stuck with the usual version of time, or you have two break the universe into two pieces, each with a different version of time. Which would be a perfectly valid thing to do if there are no interactions. Don't tell me you think there's a concept of absolute time! Time is what matter does, and theoretical analysis of what matter does depends on the idealization that is being analyzed. Time in the "real universe"? What's that? Nothing used in physics, I assure you-- physics is local, but repeatable. it is only this repeatability, coupled with similarity of initial conditions, that gives us the illusion that the universe supports a global concept of time.


You are playing the game of the "lanscape" string physicists and looking at alternate universes with alternate laws, based only on the mathematics that governs the consistency of those laws and placing some sort of reality on them. Heavens no, you know my opinion of that stuff, it isn't physics. What I'm doing is physics, no pretensions of "real" universes that cannot be measured, just idealizations to treat what can be measured.

please
2009-Jul-24, 07:26 AM
What is the show stopper is A --> B --> not A.any chance to see Feynman diagram for this from you?

grant hutchison
2009-Jul-24, 10:38 AM
There are such closed time-like solutions in GR. See the Godel metric for an example. And the region between event horizons in the Kerr metric also allows closed time like curves (but such an obscenity is causally disconnected from the outside universe by the outer horizon).And after Godel's rotating universe and Kerr's decently shrouded mischief, the closed timelike curves started threatening to come out where we could see them in 1974, with Tipler's Rotating cylinders and the possibility of global causality violation (http://www.geocities.com/theophysics/tipler-rotating-cylinders.pdf) (300KB pdf).

Grant Hutchison

Ken G
2009-Jul-24, 12:56 PM
Note that Tipler interprets closed timelike loops as a "time machine". I doubt it-- the wave function of a particle in a closed timelike loop would experience such destructive interference that only strictly periodic behavior would be possible. This would also have to apply to macro objects, via the correspondence principle. Hence, time would be "modded out" in such a loop, and no time travel would occur, it would merely create a pocket of proper time that is finite instead of infinite in duration. It would be a macro version of a Bohr atom-- unless the spacetime was dynamical so the loop was not cyclic (but that's not the situation he solved, so who knows what would happen there).

grant hutchison
2009-Jul-24, 02:11 PM
Note that Tipler interprets closed timelike loops as a "time machine". I doubt it-- the wave function of a particle in a closed timelike loop would experience such destructive interference that only strictly periodic behavior would be possible.Isn't it the case that the "time machine" resides not in the closed timelike curve itself, but in the family of "nearly closed" curves in its near vicinity, which allow an object to manoeuvre into its own past light cone?
That seems to be the approach taken by "The Consortium" in the late 80s and early 90s, when they explored causality in the vicinity of closed timelike curves. See, for instance, Billiard balls in wormhole spacetimes with closed timelike curves: Classical theory (http://authors.library.caltech.edu/6469/). (I've never been able to track down the promised successor paper in which QM is applied to the situation.)

Grant Hutchison

timb
2009-Jul-24, 02:41 PM
And after Godel's rotating universe and Kerr's decently shrouded mischief, the closed timelike curves started threatening to come out where we could see them in 1974, with Tipler's Rotating cylinders and the possibility of global causality violation (http://www.geocities.com/theophysics/tipler-rotating-cylinders.pdf) (300KB pdf).


I thought Hawking had disproved Tipler cylinders. Another method involves wormholes, which is perhaps an argument for their nonexistence, though I believe Visser has a solution to that. Bring the temporally separated mouths of a wormhole together and it turns into a singularity!

grant hutchison
2009-Jul-24, 02:46 PM
I thought Hawking had disproved Tipler cylinders. I believe Hawking showed that Tipler's conjecture about creating closed timelike curves around finite cylinders would violate the Weak Energy Condition.
It's all part of Hawking's "Chronology Protection Conjecture", so I'm not sure that the word "disprove" applies, unless things have changed recently.
Kip Thorne gives a review of the various problems here (http://www.its.caltech.edu/~kip/scripts/ClosedTimelikeCurves-II121.pdf) (1.3MB pdf), albeit a decade old now.

Grant Hutchison

loglo
2009-Jul-24, 03:24 PM
There are such closed time-like solutions in GR. See the Godel metric for an example. And the region between event horizons in the Kerr metric also allows closed time like curves (but such an obscenity is causally disconnected from the outside universe by the outer horizon). ....

-Richard

Does that mean if you fall into a rotating black hole you can be spaghettified again and again and again ....... ??? Sounds like something out of Itchy and Scratchy! :)

DrRocket
2009-Jul-24, 04:35 PM
I never said it did-- indeed, I said the opposite, that our notions of causality must embrace perfectly periodic systems so that we not make claims on causality that are insufficiently general.

Of course. But any notion if causality that in broadly applicable to physical laws that govern the universe will of necessity be applicable to periodic phenomena within that universe. Causality is a question that is of such generality as to apply to all of physics.

My point is that any such concept, because of that generality, must be applicable to other than periodic phenomena as well. It is not valid to use periodicity to modify the very concept of the universe by "modding out" time. When you do that you have a simplified model for some purposes, but not one that is applicable to discussions of causality.


Actually, you do. This is the full meaning of an equivalence class.

No, actually you don't. I am rather well acquainted with the meaning of equivalence classes.

If you want to work within the context of some sort of equivalence classes that is just fine. But when you do that you have to accept the whole enchilada, not just the parts that are convenient for your argument.

In the case of periodic systems, that means working within a context in which everything is describable in terms of your equivalence classes, in which all phenomena are describable as periodic with periods that are accommodated with the equivalence classes that you have chose, and hence in a periodic universe. That is the point with the example of a universe with two harmonic oscillators with non-commensurate periods -- you can't set up equivalence classes that work there.


As I said, it is a standard device in deriving laws of physics to consider such simplified systems as though they were microcosms. Indeed, I know of no other situations in which laws are derived.

Then pick up a physics text. Any physics text.

There is a difference between "deriving the laws of physics for simplified systems" and "applying the laws of physics to simplified systems".

A valid law of physics should, in principle be applicable to the entire universe. Now, we know that the actual laws that we do have are more limited and have a domain of validity that is less encompassing, but in principle the objective is to be universally applicable.

It is quite common, and proper, when attempting to understand physical law to apply that law to simplified situations, to conduct gedanken experiments. The purpose is not to derive laws that are applicable only to the situation of those experiments, but rather to apply laws with general applicability and to determine the implications of those laws, perhaps to uncover an inconsistency in those laws (as was the intent of Einstein's challenges to quantum mechanics), perhaps to illuminate the implications of those laws (the common application of such examples in physics text books), and perhaps to simplify the mathematical model so as to make the analysis amenable to hand calculations (part of the illumination objective). It is not to derive laws that are applicable only to the specific idealization at hand.

Models that are applicable only to specific simplified systems are not usually called physical laws, but rather are called approximations.


As I said, this is not a valid criticism of any law of physics, as there are no known laws that survive it. Symmetries are broken, principles are violated, willy nilly. Not a one of them is meant to be anything but an idealization, applying to idealized systems that are never the universe "at large". Even the cosmological principle, the sole inherently "at large" principle in all of physics, is really nothing but a useful idealization.

Hardly.

The basic physical laws are intended to apply universally. There is in principle no limitation on the scale to which either quantum mechanics or general relativity would apply. In reality we find that the laws as we know them, run into difficulties with logical consistency between them (QM and general relativity for instance), problems with internal consistency (mathematical problems with QFT at arbitrary energy scales) and our inability to rectify those problems at this stage of the game. But the goal of those pursuing "theories of everything" is to develop fundamental laws that do not have those limitations.

We are in total agreement that the "cosmological principle" is nothing but a useful idealization. That is the point. It is not a real physical principle at all. It is an idealization intended to simplify the mathematics applicable to cosmology. Nothing more. In that context it permits cosmologists to talk about "time" and "space" at cosmological scales despite the fact that a rigorous application of general relativity would preclude such a discussion.




You're not getting it. When the energy levels of a hydrogen atom are calculated, it is done as though the atom is alone in the universe. No one says "that's an invalid calculation, because I can imagine a universe with two atoms in it." We put in a second atom when we want to explore different kinds of interactions, and the laws that relate to them. It's the choice of the physicist exploring the laws, we are never required to put the whole universe into every law! That has simply never been the way physics is done.

I get it just fine.

When the energy levels of the hydrogen atom are calculated it is done with the idealization that the atom has no interactions with other atoms. It is done with the same physical laws that would apply to the hydrogen atom as one of many in a gas. One simply neglects those interactions.

One does not formulate one set of physical laws for a universe of one hydrogen atom, and another, different set, of physical laws for a universe with one hydrogen atom and a second helium atom. The laws are the same, but the simplified models are different.

The same quantum laws that are used to describe one hydrogen atom apply to the entire universe. You can take advantage of periodicity to simplify the mathematics of the single atom, but you don't get to "mod out time" for the universe at large.

In short, "modding out time" for a periodic model has no bearing whatever on the question of causality in the context of the real universe.


Consider for example the second law of thermodynamics, that entropy increases in the spontaneous evolution of large closed systems. I could try to define a concept of entropy for a system of five particles, but there'd be no advantage, because the law wouldn't apply there. We would not then say "you can't talk about a universe of five particles because the real universe has more than that", we just say "the second law of thermodynamics doesn't apply to five particles." It's about understanding the limitations of our laws, and their proper realm of applicability. I'm saying causality has similar limitations, and we should not make blindly broad claims like you can't have a closed time-like loop because it violates causality.

The second law of thermodynamics is a statistical concept. You can apply it to five particles if you wish, but when you do that you cannot apply the law of large numbers. The basic principles continue to apply. As always, you need to verify the truth of the hypotheses before applying mathematical theorems to the physical situation.

The statement that "you can't have a closed time-like loop because it violates causality" is not very meaningful. By definition, if causality is a requirement then you can't have closed time-like loops that describe a physical event, and if you have no such loops then you have causality.

The question is whether or not causality is a requirement of physics.

There are two ways one might approach that question.

One would be to simply demand causality, determine what that implies in terms of the mathematical descriptions of physical laws, and then attempt to confirm or refute the postulate of causality experimentally. In that case causality is nothing more and nothing less than an assumption that is open to experimental challenge. Ordinary experience would indicate that any experiment that would refute the assumption of causality would have to involve circumstances that are somewhat exotic. But that is not a big deal since most modern physics experiments are pretty exotic.

The other way is to ask if causality is implied by the laws of physics that are accepted and supported by the broad body of accepted physics. That still leaves causality open to experimental refutation, but it serves to determine if it is a separate assumption or one that comes along "for free" with other assumptions. It turns out that you get causality "for free" if you assume that you cannot propagate information at faster than the speed of light in special relativity. In reality, all that says is that there are different ways to state what "causality" means.


Which would be a perfectly valid thing to do if there are no interactions. Don't tell me you think there's a concept of absolute time! Time is what matter does, and theoretical analysis of what matter does depends on the idealization that is being analyzed. Time in the "real universe"? What's that? Nothing used in physics, I assure you-- physics is local, but repeatable. it is only this repeatability, coupled with similarity of initial conditions, that gives us the illusion that the universe supports a global concept of time.

Of course, I am not saying there is any concept of "absolute time'.

In fact in general relativity there is no concept of global time at all. More precisely, there is no concept of time on the space-time manifold. It is a concept that is limited to the tangent bundle and applies only approximately and locally on the actual space-time manifold, unless the manifold is actually flat and the tangent bundle is trivial. We know that the manifold is not flat (your bathroom scale tells you that).

What does appear to exist is some version of invariance of order of events. That is a bit more subtle than a global notion of time. The question is whether or not the order of events is invariant.

As to whether physics is local or not, that remains an open question. GR most certainly treats physics as local. There are quantum phenomena that call locality into question. What is the answer ? I dunno. If I figure it out, I'll PM you from Stockholm.



Heavens no, you know my opinion of that stuff, it isn't physics. What I'm doing is physics, no pretensions of "real" universes that cannot be measured, just idealizations to treat what can be measured.

But you do not and cannot make measurements in an idealized universe. Your laboratory is stuck in this one. Any measurement that you make must apply to the "real" universe. It is the only universe that is available.

You cannot take measurements of idealizations. That is the blessing and the curse of experimentalists. They simply do not have access to spherical cows.

You can only formulate idealizations for the purpose of gedanken experiments and the simplification of mathematical models.

So, you formulate physical laws with the expectation that they apply to the real universe, then you devise simplified mathematical models that let you actually solve the resulting equations and compare them with measurements made in real laboratories in the real universe.

There is gigantic difference between an idealized, simplified model of a phenomena that occurs in our universe, and some physical law that applies only in some simplified universe.

The notion of causality is applicable to our universe, and what that means in some hypothetical periodic universe, with some hypothetical periodic version of time, perhaps containing only a single hydrogen atom, is not relevant.

Ken G
2009-Jul-24, 04:51 PM
Isn't it the case that the "time machine" resides not in the closed timelike curve itself, but in the family of "nearly closed" curves in its near vicinity, which allow an object to manoeuvre into its own past light cone?Perhaps so, that might make a lot more sense. I'll have a look at your link.

grant hutchison
2009-Jul-24, 05:09 PM
Perhaps so, that might make a lot more sense. I'll have a look at your link.Thorne's Closed Timelike Curves (http://www.its.caltech.edu/~kip/scripts/ClosedTimelikeCurves-II121.pdf) (1.3MB pdf) might also be of interest.

Grant Hutchison

publius
2009-Jul-24, 07:01 PM
any chance to see Feynman diagram for this from you?

Well, we're talking world lines (or paths information can take, better). They're similiar to Feynman diagrams, but not the same thing. And example of A --> B --> not A is just the Grandfather paradox. Why we have to bring two generations in it, I don't know. Why not the self paradox, where you go back in time and shoot yourself? :lol: This is where the effect of a cause is to prevent the cause from happening.


-Richard

Ken G
2009-Jul-24, 07:37 PM
Thorne's Closed Timelike Curves (1.3MB pdf) might also be of interest.
Tough sledding that, but you are right that the closed timelike loops are not actually followed by the world lines of interest, as you say, those world lines are navigating manifolds that merely contain timelike loops in them. It's really a study of locally normal spacetimes that connect to asymptotically flat spacetimes but which contain topological "defects" of some kind, which allows world lines to fold back into their own past light cones. Something of that nature. That seems to be what Tipler was talking about too-- introducing defects into the spacetime that have closed timelike loops, but not considering the worldlines that are actually on those loops. The future could then send signals that affect the past without being periodic, which is not necessarily inconsistent, but which is indeterminate because you'd need to know what is going to happen to understand what is going to happen.

A greater problem might be that it breaks the structure of what physics is, so I wonder about the validity of even using physical laws obtained by doing physics to attempt to analyze a situation where the methods of physics won't work. If we routinely functioned in a spacetime like that, could we have learned about it via the process we now call physics? If not, how is what we have learned relevant to that situation?

publius
2009-Jul-24, 08:04 PM
OK you can do that. But that has nothing to do with Minkowski. All that you are really saying is that Minkowski is just 4-space with some non-degenerate metric. So forget the metric and just connect two points with a line, or a curve. The fact that it is not time-like we just ignore. There is no distinguished class of vectors or curves and we are simply ignoring the natural geometry imposed by the Minkowski metric. Or, if you don't allow simply going back along the time axis, or similar things, you are basically back in the Newtonian case where there is no speed limit and the symmetry group is the Galilean group.

I think that when you "ponder the consequences" in this case you may find that they are unacceptable from a physical perspective.

You can do the same thing in GR, just as easily. The manifold is connected, so you can join any two points with a curve. That curve won't necessarily be a geodesic. God only knows what the significance of such a thing is. I presume, however, that your example using the Kerr metric, does involve geodesics. That is a bit more interesting.

I think we were sort of misunderstanding each other. That's pretty much what I meant -- we can see the potential paradox by allowing information to follow a closed loop, and we can see that in simple Minkowski space. There (and in non-obscene curved space-times), such closed paths necessarily involve moving faster than light.

Now, about the closed time-like curve solutions. It's not just geodesics, but just any general closed time-like path that becomes possible (non geodesic would be an accelerated path, of course). We can imagine a space-time where geodesics didn't close, but by accelerating, we could form a closed path.

However, I think there's something that if closed time like curves can exist, then there must be some null geodesics, light paths, that close in on themselves. If CTLCs are possible, then the light cone has to bend back around which is going to mean that light at least much form a closed path at some points. For example, in the Godel spacetime, you can look out in the distance and see your own past from your own light boomeranging back to you.

Also, note all the above examples involve rotation. CTLCs are a characteristic of extreme frame dragging, gravitomagnetism run amok. Consider a light cone that gets bent around at some point, say 90 degrees. You can see that there, a particle cannot stay stationary, but must move, as the future at the same point in space is outside the light cone. "Must move" is a characteristic of frame dragging past a stationary limit where inertial space must move.

-Richard

DrRocket
2009-Jul-24, 08:24 PM
Tough sledding that, but you are right that the closed timelike loops are not actually followed by the world lines of interest, as you say, those world lines are navigating manifolds that merely contain timelike loops in them. It's really a study of locally normal spacetimes that connect to asymptotically flat spacetimes but which contain topological "defects" of some kind, which allows world lines to fold back into their own past light cones. Something of that nature. That seems to be what Tipler was talking about too-- introducing defects into the spacetime that have closed timelike loops, but not considering the worldlines that are actually on those loops. The future could then send signals that affect the past without being periodic, which is not necessarily inconsistent, but which is indeterminate because you'd need to know what is going to happen to understand what is going to happen.

I think what you are suggesting is that these models introduce a topology to space-time that is not simply connected (I surmise that is what you mean by "defects". That would seem a natural way to violate causality. It is the effect of "wormholes" the effect of which is to introduce non-trivial elements of the first homotopy group (which means that the space is not simply connected). You are essentially attaching tubular handles to a surface (really the equivalent in higher dimensions). That is pretty radical stuff.

Periodicity won't do the trick. To be truly periodic, a function must be periodic for all time. In the case of the universe that should mean from the big bang onward. For most idealizations that means from minus infinity to infinity. From a mathematical perspective it means the function is invariant under some group of translations, and generally we are talking about ordinary translations over the entire real line. If you have a system that is truly periodic (from minus infinity onward), the very notion of causality becomes moot, since there is no such thing as an initial condition.




A greater problem might be that it breaks the structure of what physics is, so I wonder about the validity of even using physical laws obtained by doing physics to attempt to analyze a situation where the methods of physics won't work. If we routinely functioned in a spacetime like that, could we have learned about it via the process we now call physics? If not, how is what we have learned relevant to that situation?

This is precisely the problem with attempting to use an imaginary universe, such as one with only a single hydrogen atom, to reach broad conclusions about the universe in which we live.

These exercises are useful in understanding the limits of the mathematics that is applied to the real universe. But one cannot conclude from such extreme examples that the weirdness that is found actually applies to our universe. One must consider the accuracy and applicability of the use of these imaginary universes as approximations to the real thing.

For some applications the idealizations are indeed accurate enough to provide useful answers -- as is the case when on calculates the energy states of the hydrogen atom while ignoring all outside interactions. But for other applications the idealizations may be so representative of reality.

DrRocket
2009-Jul-24, 08:26 PM
I think we were sort of misunderstanding each other. That's pretty much what I meant -- we can see the potential paradox by allowing information to follow a closed loop, and we can see that in simple Minkowski space. There (and in non-obscene curved space-times), such closed paths necessarily involve moving faster than light.

Now, about the closed time-like curve solutions. It's not just geodesics, but just any general closed time-like path that becomes possible (non geodesic would be an accelerated path, of course). We can imagine a space-time where geodesics didn't close, but by accelerating, we could form a closed path.

However, I think there's something that if closed time like curves can exist, then there must be some null geodesics, light paths, that close in on themselves. If CTLCs are possible, then the light cone has to bend back around which is going to mean that light at least much form a closed path at some points. For example, in the Godel spacetime, you can look out in the distance and see your own past from your own light boomeranging back to you.

Also, note all the above examples involve rotation. CTLCs are a characteristic of extreme frame dragging, gravitomagnetism run amok. Consider a light cone that gets bent around at some point, say 90 degrees. You can see that there, a particle cannot stay stationary, but must move, as the future at the same point in space is outside the light cone. "Must move" is a characteristic of frame dragging past a stationary limit where inertial space must move.

-Richard

I can agree with all of this.

DrRocket
2009-Jul-24, 08:44 PM
Also, note all the above examples involve rotation. CTLCs are a characteristic of extreme frame dragging, gravitomagnetism run amok. Consider a light cone that gets bent around at some point, say 90 degrees. You can see that there, a particle cannot stay stationary, but must move, as the future at the same point in space is outside the light cone. "Must move" is a characteristic of frame dragging past a stationary limit where inertial space must move.

-Richard

Do you happen to know if these phenomena that produce CTLCs have been studied using Einstein-Cartan theory rather than GR? Since EC seems to handle spin better than does GR, it would be interesting to know if, like the singuarities in black holes, the CTLCs go away in EC.

Ken G
2009-Jul-24, 08:47 PM
But any notion if causality that in broadly applicable to physical laws that govern the universe will of necessity be applicable to periodic phenomena within that universe. And from that it follows that anything that is true about causality in a periodic system must be embeddable into any generally true statement about causality, which was my point. You claimed that it could not be consistent with physics for A --> B --> A, but in periodic systems we find an example where it is consistent with physics. Thus we logically cannot conclude it is impossible for A --> B --> A, we simply don't claim either that it is always possible. We say it is possible in some situations, such as a ball bouncing between two walls in a perfectly periodic configuration, like a 1D universe with no forces and perfectly elastic walls, where A is bouncing off one wall and B is bouncing off the other.


My point is that any such concept, because of that generality, must be applicable to other than periodic phenomena as well.Now you are talking about a totally different kind of law. You are now asking about what law can always be true, but you were earlier talking about something that you claimed could never be true. I know you are a better logician than that! You are basically saying "anything that is ever true about causality has to always be true about causality", and I'm asking "how come?", and gave you the example of the second law of thermodynamics, a law that is not always true because it has a domain of applicability.


No, actually you don't. I am rather well acquainted with the meaning of equivalence classes.Then you should certainly know that perfectly periodic motion generates the equivalence class on time, via the relation [t] = t + nP where P is the period and n is any integer. That equivalence relation is the definition of perfectly periodic motion.

In the case of periodic systems, that means working within a context in which everything is describable in terms of your equivalence classes, in which all phenomena are describable as periodic with periods that are accommodated with the equivalence classes that you have chose, and hence in a periodic universe. No, that argument has the identical logical content to claiming that even and odd integers don't form equivalence classes over the set of all integers, on the grounds that irrational numbers are being left out.


That is the point with the example of a universe with two harmonic oscillators with non-commensurate periods -- you can't set up equivalence classes that work there. And you can't set up even/odd equivalence classes with irrational numbers. The point is irrelevant.


Then pick up a physics text. Any physics text.
There is a difference between "deriving the laws of physics for simplified systems" and "applying the laws of physics to simplified systems".
I'm afraid it is you who need to pick up any physics text. Find a derivation, any derivation, and tell me that the difference you claim can be identified. Laws of physics apply to simplified systems, because they all involve idealizations. Every single one, with no exception. It is pure philosophy that they should apply in detail, and is never demonstrably correct. Google "error bars", or look at the history of science.



A valid law of physics should, in principle be applicable to the entire universe.Again, pure philosophy. Physics is about what is demonstrably true, there is no physics "in principle", it is a pragmatic endeavor to the core, that uses principles because it is pragmatic to do so. That's just what it is, and always has been-- the use of principles really confuses people on this point (especially mathematicians!).


Now, we know that the actual laws that we do have are more limited and have a domain of validity that is less encompassing, but in principle the objective is to be universally applicable.The first half of that statement has meaning and is correct, the second half has none. It can't be talking about physics, because the terms are not even defined in physics.


It is quite common, and proper, when attempting to understand physical law to apply that law to simplified situations, to conduct gedanken experiments.This is more than "common and proper", it's physics.


Models that are applicable only to specific simplified systems are not usually called physical laws, but rather are called approximations. That's complete hooey. The vast majority of all that is physics is intended to be applied only to specific simplified systems. Just glance at the table of contents of any physics book you like.


When the energy levels of the hydrogen atom are calculated it is done with the idealization that the atom has no interactions with other atoms. It is done with the same physical laws that would apply to the hydrogen atom as one of many in a gas. One simply neglects those interactions.Then it is not done with the same physical laws! That's what "neglect" means.

The second law of thermodynamics is a statistical concept.Yes, it certainly has that attribute. It is a law, it has various attributes. Like all laws.


You can apply it to five particles if you wish, but when you do that you cannot apply the law of large numbers. The basic principles continue to apply. No, the "basic principles" are the principles of large numbers, so they do not apply. There is a lot about physics that you really don't get!


By definition, if causality is a requirement then you can't have closed time-like loops that describe a physical event, and if you have no such loops then you have causality.By a wrong definition only, that's my point. I gave you an example of why the definition of causality you seem to have in mind is not suitably general, ergo it is the wrong definition for that general concept.

The question is whether or not causality is a requirement of physics.
No, the question is how to define causality such that it is a requirement of physics. We are not hemmed in by our own faulty definitions, we change them to make them work. Look at wave/particle duality for a classic example-- we did not say "can we use the concept of a particle in physics", we said "how can we use the concept of a particle in physics." The definition of particle changed, as it probably will many times over.

It turns out that you get causality "for free" if you assume that you cannot propagate information at faster than the speed of light in special relativity.But that's not responsive to the issue at hand, which is what is the definition of causality. Nothing in my bouncing ball model involves any information traveling faster than light, yet A -> B -> A in the quotient set of time that parametrizes all our experiments on such a system. We can work in the original set, rather than the quotient set, only because our measurements couple the system to nonperiodic systems. But that is something we have added to the system that is clearly not part of the system before we started interacting with it. It is a classic example of a measurement effect, not a system effect.


In fact in general relativity there is no concept of global time at all. Exactly my point.


More precisely, there is no concept of time on the space-time manifold. It is a concept that is limited to the tangent bundle and applies only approximately and locally on the actual space-time manifold, unless the manifold is actually flat and the tangent bundle is trivial. I thought you just said the laws of physics were something different from the approximations we use to apply them. Try deriving the laws of physics without the concept of time, which you have just labeled as "approximate". You just need to step back and see physics for what it is. You certainly know how to do physics theory, just track what you're doing!


What does appear to exist is some version of invariance of order of events.I know, my point is that an order of events can be a local relation rather than a global one. When the second hand of a clock goes around, we have no problem with time ordering the ticks just from what we see on that clock-- until we consider times longer than a minute. Is not 5+1 = 6, even when we are considering the integers mod 10? You are simply assuming that time ordering has to be a global property, even though you assert that there is no global concept of time!


GR most certainly treats physics as local. There are quantum phenomena that call locality into question. What is the answer ? I dunno. Entanglement rules out naive locality, but it doesn't mean that we are not still correlating the outcomes of local experiments. Saying physics is local does not preclude correlations, not even correlations that violate Bell's inequality. It just means one needs a more sophisticated definition of local. The locality of physics stems from nothing but the simple fact that all observational tests of physics are local measurements.

But you do not and cannot make measurements in an idealized universe. Your laboratory is stuck in this one. Any measurement that you make must apply to the "real" universe. It is the only universe that is available.Again, I refer you to the basic structure of physics, as outlined in any physics textbook. Look at the chapter titles, look at the figures in the book, look at the variables in the equations. Not a one will be the "real" universe, they will all be vastly idealized. This is the whole point of physics-- we already have the "real" universe.

afterburner
2009-Jul-24, 08:52 PM
So, when a unicorn pops a ballon in my dream, does that mean that the unicorn caused my balloon to pop?

please
2009-Jul-24, 09:15 PM
Well, we're talking world lines (or paths information can take, better). They're similiar to Feynman diagrams, but not the same thing. And example of A --> B --> not A is just the Grandfather paradox. Why we have to bring two generations in it, I don't know. Why not the self paradox, where you go back in time and shoot yourself? :lol: This is where the effect of a cause is to prevent the cause from happening.yes well, the world lines, whatever, where is the drawing? ;) ;)

publius
2009-Jul-24, 09:21 PM
Do you happen to know if these phenomena that produce CTLCs have been studied using Einstein-Cartan theory rather than GR? Since EC seems to handle spin better than does GR, it would be interesting to know if, like the singuarities in black holes, the CTLCs go away in EC.

That's a darn good question, and I just don't know. As you know I'm sure, E-C is much more complex than regular GR, and there just hasn't been a real need to study it. I'd love for some of the best and brightest to explore E-C much more than they have. Who knows what would pop out.

However, in this case, I believe that torsion, which is rotation-like of course, can do even more obscene things! There's something about Ehrenfest's "paradox" there. Ehrenfest is just a coordinate problem, but torsion can make that quirk be "real", putting it in the space-time itself, IIRC. But I don't understand it much at all, other than torsion can do really weird things.

-Richard

DrRocket
2009-Jul-24, 10:47 PM
And from that it follows that anything that is true about causality in a periodic system must be embeddable into any generally true statement about causality, which was my point. You claimed that it could not be consistent with physics for A --> B --> A, but in periodic systems we find an example where it is consistent with physics. Thus we logically cannot conclude it is impossible for A --> B --> A, we simply don't claim either that it is always possible. We say it is possible in some situations, such as a ball bouncing between two walls in a perfectly periodic configuration, like a 1D universe with no forces and perfectly elastic walls, where A is bouncing off one wall and B is bouncing off the other.
Now you are talking about a totally different kind of law. You are now asking about what law can always be true, but you were earlier talking about something that you claimed could never be true. I know you are a better logician than that! You are basically saying "anything that is ever true about causality has to always be true about causality", and I'm asking "how come?"

You have completely perverted what I said.

It is NOT true that anything true about a quotient space is true about the original space. That is trivial.

And that is the point. In your example of periodic systems you have not only "modded out" time, you have invoked a definition of both time and causality that does not carry over to the original space. So conclusions that you reach regarding the quotient space do not pull back to the original space.




No, that argument has the identical logical content to claiming that even and odd integers don't form equivalence classes over the set of all integers, on the grounds that irrational numbers are being left out.
And you can't set up even/odd equivalence classes with irrational numbers. The point is irrelevant.

All this shows is that you don't understand what an equivalence relation is, or what equivalence classes really are.

Any partition of a set into a union of disjoint subsets can establish equivalence classes. It is commonly imposed by a transitive relation, but in fact any partition will do the trick.

Even and odd integers clearly represent a bi-modal partition of the integers into equivalence classes. So does {0} and {all non-zero integers}. It is not an equivalence relation on the real numbers, for the elementary reason that we have not addressed the real numbers. But you can do that in many ways, one of which is just {{even integers},{odd integers},{all non-integer real numbers}}. So what ?

The point is that if you prove some theorem regarding the integers mod even/odd (equivalent to the integers mod 2 by the way), there is very little that you can conclude from that theorem regarding the entire set of integers or the set of real numbers.

When you work in a quotient space, your conclusions apply to the quotient space. If you make up a definition in the quotient space, say regarding what you mean by time or by causality, that definition and conclusions that you reach from it apply only to the quotient space.

We don't live in your quotient space.


I'm afraid it is you who need to pick up any physics text. Find a derivation, any derivation, and tell me that the difference you claim can be identified. Laws of physics apply to simplified systems, because they all involve idealizations. Every single one, with no exception. It is pure philosophy that they should apply in detail, and is never demonstrably correct. Google "error bars", or look at the history of science.

Nonsense. That is why we have "Newton's Laws of Motion" and not "Newton's laws of tops" + "Newton's laws of bullets" + "Newton's laws of satellites" + "Newton's laws of baseballs" + ...



=That's complete hooey. The vast majority of all that is physics is intended to be applied only to specific simplified systems. Just glance at the table of contents of any physics book you like.

It is precisely the table of contents of any physics book that supports my position and refutes yours. It is why "Newton's Laws of baseballs" does not appear in the table.


No, the "basic principles" are the principles of large numbers, so they do not apply. There is a lot about physics that you really don't get!

I think it is you who are not getting this one. There is no such thing as "the principles of large numbers". There is a very specific theorem in probability theory called "The Law of Large Numbers". It is what allows you to relate statistics to probability. They are not the same thing.



By a wrong definition only, that's my point. I gave you an example of why the definition of causality you seem to have in mind is not suitably general, ergo it is the wrong definition for that general concept.
No, the question is how to define causality such that it is a requirement of physics. We are not hemmed in by our own faulty definitions, we change them to make them work. Look at wave/particle duality for a classic example-- we did not say "can we use the concept of a particle in physics", we said "how can we use the concept of a particle in physics." The definition of particle changed, as it probably will many times over.

But you have not offered any alternate definition of causality.

If you have something different than a condition in which all observers will agree on the order of events, then state it.

But you should also be prepared to justify it "philosophically" as being an appropriate modification of the usual definition.


But that's not responsive to the issue at hand, which is what is the definition of causality. Nothing in my bouncing ball model involves any information traveling faster than light, yet A -> B -> A in the quotient set of time that parametrizes all our experiments on such a system. We can work in the original set, rather than the quotient set, only because our measurements couple the system to non-periodic systems. But that is something we have added to the system that is clearly not part of the system before we started interacting with it. It is a classic example of a measurement effect, not a system effect.

No you can't. You don't in fact really work in the quotient set that is suggested by periodicity. That quotient set only applies to functions that are no-kidding periodic. That means they repeat indefinitely in both the direction of positive time and of negative time. You would have to have started your experiment infinitely long ago and continue it forever into the future to be truly working the quotient space in which you claim to be working. (Bad news -- you would never be able to publish the results because the experiment would go on forever. Experiments never go on forever, but only seem to do so for PhD candidates in experimental disciplines.)



I know, my point is that an order of events can be a local relation rather than a global one. When the second hand of a clock goes around, we have no problem with time ordering the ticks just from what we see on that clock-- until we consider times longer than a minute. Is not 5+1 = 6, even when we are considering the integers mod 10? You are simply assuming that time ordering has to be a global property, even though you assert that there is no global concept of time!

You need to pick the context in which you want to make your point and stick to it. You are switching hypotheses without acknowledging that, so of course you run into difficulty.

Lack of a global measurement of time does not imply lack of a global concept of the ordering of events. That is precisely the case for the usual meaning of causality in special relativity -- observers all agree on the order of events even when they disagree on the measurements of their clocks.

And NO 5+1 is NOT 6 in the integers mod 10. What that means is that mod 10 {.... -5, 5, 15, 25, 35, ...} + {..., -9, 1, 11, 21, 31, ...} = {..., -4, 6, 16, 26, 36,...}. I thought you said that you understood equivalence classes.



Again, I refer you to the basic structure of physics, as outlined in any physics textbook. Look at the chapter titles, look at the figures in the book, look at the variables in the equations. Not a one will be the "real" universe, they will all be vastly idealized. This is the whole point of physics-- we already have the "real" universe.

Of course not one textbook model will be the real universe. They will be idealized. But the basic laws that are discussed are intended to model real principles in the real world. Pedagogical considerations and our ability to actually solve equations limits the models that can be intelligently discussed in a text, and even what can be calculated in practice.

That is why the models used by engineers often are more empirical than the laws considered by physicists. Exact solutions are out of reach. Complex interactions make exact models intractable. But physics and engineering have different objectives. That is why and engineer might be well-served by a "physics of tops" but a physicists aspires to something more generally applicable.

If you could just simply "solve the SchrŲdinger equation for the universe" and then sort things out, don't you think that is precisely what would be done? But, even if we thought that QM was sufficiently accurate in principle, the equations are too hard so solve so such a thing is unattainable.

But we are digressing from your original misconception. You cannot work in a quotient space and then simply pull the conclusions to the original space, without further analysis. It just doesn't work that way. In particular a definition manufactured for the quotient space may be without meaning or with a very distorted meaning when you attempt to apply it in the original space.

Take your example of periodicity, which results from treating the real numbers mod 2 pi (or mod anything other than 0). You get a circle as the quotient space. The first homotopy group of the circle is the integers (basically you count the number of times you wrap around the circle). The real numbers are homotopically trivial, in fact contractible. In short, loops on the circle do not give you loops on the line. This why your notion of causality for periodic systems is irrelevant to causality in general. The definitions do not carry over from one context to the other.

Ken G
2009-Jul-25, 01:13 AM
It is NOT true that anything true about a quotient space is true about the original space. That is trivial.At least we can now agree we are dealing with a quotient space when we discuss perfectly periodic systems.

In your example of periodic systems you have not only "modded out" time, you have invoked a definition of both time and causality that does not carry over to the original space. The point is, there is no "original" space. The quotient space is all that is demonstrable or testable about, it is the whole system.

The same principle appears when we do two-dimensional dynamics in polar coordinates-- the axial coordinate is obviously a quotient space, why don't you worry about the "real space" of all those extra multiples of 2pi? I merely apply the same principle to time in a system coordinatized via periodic time. Time is as time does, just like position. (And note that in Fermion systems in quantum mechanics, we do not return to the original configuration with a 2pi rotation, we return to the negative of the original wavefunction. So here we have another example of how the "laws" work-- some laws treat a 2pi rotation like the identity, others do not. We have no idea if any rotation "really is" the identity, that's not the kind of question physics answers in any way but conditional to a particular theory and particular types of idealized systems.)



All this shows is that you don't understand what an equivalence relation is, or what equivalence classes really are.Actually, you see that I have never misapplied the term in the least. The problem is that you don't know what physics is.

The point is that if you prove some theorem regarding the integers mod even/odd (equivalent to the integers mod 2 by the way), there is very little that you can conclude from that theorem regarding the entire set of integers or the set of real numbers.Obviously. Further, I hope I have now shown you the irrelevance of that entire remark.

We don't live in your quotient space. Good lord man, we don't live in any physics theory! We live in the real world, and like I said, we already have that, we don't need another. We need physics theories.


Nonsense. That is why we have "Newton's Laws of Motion" and not "Newton's laws of tops" + "Newton's laws of bullets" + "Newton's laws of satellites" + "Newton's laws of baseballs" + ...No, but we do have "Newton's laws of motion of rigid objects", and "Newton's laws of motion of point particles", etc. You just never realized this. Look at any table of contents of a physics book, really.


It is precisely the table of contents of any physics book that supports my position and refutes yours. It is why "Newton's Laws of baseballs" does not appear in the table.That's only because you have no idea what I'm talking about when I say "idealized systems" (hint: not baseballs).

There is no such thing as "the principles of large numbers".I'm afraid you are not not getting what I'm saying at all. There are indeed principles in physics that apply to systems containing large numbers of particles, which do not apply to smaller systems. That is what I am talking about here, and it is just a fact.

And NO 5+1 is NOT 6 in the integers mod 10. What that means is that mod 10 {.... -5, 5, 15, 25, 35, ...} + {..., -9, 1, 11, 21, 31, ...} = {..., -4, 6, 16, 26, 36,...}. You misinterpret my statement again. I said {5 + 1} mod 10 = 6 mod 10. Which it does. I am not adding equivalence classes, I am doing arithmetic. You really think one cannot do arithmetic within an equivalence class? I thought you said you understood these!




But we are digressing from your original misconception. You cannot work in a quotient space and then simply pull the conclusions to the original space, without further analysis. This is entirely your misconception, I find that mathematical truth to be perfectly obvious. Your misconception is that there is any such thing as the original space in physics, once an equivalence class has been identified. I thought you understood the Lorentz symmetry in relativity, for example!

robross
2009-Jul-25, 02:39 AM
Well I got lost several pages ago, so how about some cliff notes?

Is causality mandated by the laws of physics, or is it just an observation?

Rob

DrRocket
2009-Jul-25, 03:09 AM
Well I got lost several pages ago, so how about some cliff notes?

Is causality mandated by the laws of physics, or is it just an observation?

Rob

"Cliff notes":

It may well be that causality is a law of physics. And perhaps not, but I don't think anyone would bet heavily on that. There is a close tie between causality and c as a limiting speed for information transmittal in special relativity -- those conditions are equivalent. See e.g. Essential Relativity, Special, General, and Cosmological by Wolfgang Rindler.

Causality does not seem to be clearly mandated by general relativity, although the examples are sufficiently strange that this statement is far from iron clad. See the link to Kip Thorne's paper (http://www.its.caltech.edu/~kip/scripts/ClosedTimelikeCurves-II121.pdf) here or in the post from grant hutchison. Elsewhere, Hawking has proposed that chronology protection is a valid principle, but there remains work to justify that position.

There are some subtleties with the handling of time in GR and with causality itself in QFT that also cloud the issue.

KenG has gone off on a tangent involving quotient spaces (algebraic, topological, and geometric) that he does not understand himself. He has the math and the physics so screwed up that I give up on trying to straighten out that mess.

Ken G
2009-Jul-25, 06:19 AM
It's true there's no point in going blow-by-blow, the basic claim I am making here is clear enough. I'm arguing that prior to relativity, it was always pretty much assumed that time existed outside of the matter it was being used to describe. Time just ticks along ad infinitum, and then if you put some matter in there, the matter can respond to time. But Einstein, in his theory of relativity, introduced a new concept of time. Somehow everyone got the message that time connected with distance in strange ways that were frame dependent, but I think the deeper (and more important) message got missed-- motion isn't something that happens in time, time is part of the motion. Time is something less than we imagined, it does not have a separate existance that precedes motion or exists without motion. So a universe with no matter/fields has no motion, and no time.

So, if time is derived from motion as much as the other way around, then a periodic system can be treated with periodic time. The causality in such a system is cyclic, but that creates no problems because the system is less than we imagined it was. Once we understand one period, there is nothing more to say about the system and its causality. The causality is cyclic, A -> B -> A. It's not a violation in that system, so the concept of causality as a whole must be able to accomodate that arrangement.

The other alternative is that time itself is an observer effect, the observer brings the time into the picture. Then the fact that the observer is nonperiodic breaks the equivalence class. But the usual approach is to attempt to allow causality to exist independently of the observer.

Oh by the way, nothing DrRocket has said has anything to do with what I have said, I just pointed out that there is no universal requirement in physics to exclude causalilty relationships like A-->B-->A, and I gave a specific example of why, explained above. (What a concept, a specific example to support my claims.) Nor has he established a single problem with my use of the concept of equivalence classes, only with his misunderstanding of my use of the concept. The point he misses is that objective physics requires that the appearance of equivalence classes forces the actual physical theory to act on the quotient space, the rest is physically meaningless. That is the concept of a symmetry in physics, in a nutshell.

publius
2009-Jul-25, 06:39 AM
yes well, the world lines, whatever, where is the drawing? ;) ;)


Draw yourself an x-t coordinate system. Now draw a circle. That's an example of a closed curve in spacetime. :) A particle comes back to the same point in spacetime as it was before.

If that x-t diagram is in Minkowski space, that path is space-like and no particle or infomation as we understand it can follow such a path. However, in GR, valid spacetime geometries can curve in certain extreme ways to allow such a closed path to be time-like, and particles and information can follow them. Hence the term closed time-like curve, CTLC.

Such things are considered to be obscene as they offend our sensibilities of causality, and most hope that the universe will prevent such things from happening. :lol: But no ironclad prohibition has yet been found and proven to absolutely prevent then in all cases.

And Ken, if you read Kip Thorne's paper that Grant linked, you'll see he does ponder a micro vs. macro situation where maybe the chronology protection is macro only. CTLCs might still be micro, but quantum stuff prevents it from becomming macro, just like you were talking about.

-Richard

DrRocket
2009-Jul-25, 07:17 AM
And Ken, if you read Kip Thorne's paper that Grant linked, you'll see he does ponder a micro vs. macro situation where maybe the chronology protection is macro only. CTLCs might still be micro, but quantum stuff prevents it from becomming macro, just like you were talking about.

-Richard

He also note dthat the situation is so speculative and cloudy that it may well take a theory of quantum gravity to provide the necessary tools to resolve the questions at hand. The current tools are just not up to the job.

robross
2009-Jul-25, 03:09 PM
So, when a unicorn pops a ballon in my dream, does that mean that the unicorn caused my balloon to pop?

The first time I read this, I skipped over it without thinking about it. Then it dawned on me how profound a question it really is. Although I think it's more of a philosophical question than a scientific one.

Rob

Cougar
2009-Jul-25, 05:02 PM
I mean doesnt all the math in physics just work both ways (although maybe differently) regardless of causality?

See what you started? :lol:

please
2009-Jul-26, 12:20 PM
publius I wanted a diagram for a -> b -> not a. as I was saying, if an author or proponent of this "paradox" would care to sit down and draw it in x-t plane, for example, connecting all the events, he'd probably resolve the paradox in a process.

cougar I am trying to read direct responses, it's impossible to keep up with multiperson discussion.

loglo
2009-Jul-26, 12:49 PM
publius I wanted a diagram for a -> b -> not a. as I was saying, if an author or proponent of this "paradox" would care to sit down and draw it in x-t plane, for example, connecting all the events, he'd probably resolve the paradox in a process.

cougar I am trying to read direct responses, it's impossible to keep up with multiperson discussion.

Or they might come up with something like this (http://planetperplex.com/en/item160). Impossible, but real in a reduced dimensional form. I'm not trying to be facetious, I just don't think a ST diagram is enough by itself to provide a resolution to these issues.

publius
2009-Jul-26, 11:39 PM
publius I wanted a diagram for a -> b -> not a. as I was saying, if an author or proponent of this "paradox" would care to sit down and draw it in x-t plane, for example, connecting all the events, he'd probably resolve the paradox in a process.



I'm afraid I'm a bit puzzled. Closed time-like curves lead to real, no-question-about-it paradoxes. The famous example is the Grandfather paradox. That is A -- > B --> notA for sure.

Or elimate the extra two generations. I make use of a CTLC space-time, a "non-chronal" region of space-time, and go back in time, encountering myself at earlier position on my world line. I pull out a gun and blow my earlier self away. My earlier self thus cannot complete the portion of the world line that came back around. That makes for an inconsistent state of affairs. It's insanity.

And example of A --> B --> A, would be the same time machine, but there, rather than killing myself, I prevent myself from being killed, say blowing away a murder who was just about to kill my earlier self, who was unaware of the danger. That is not inconsistent. It's weird, but no a show stopper. However, if you can do one, you can do the other.

And besides that, there's the crazy possiblity of stuff, mass-energy that exists only in a closed time like curve. It does not exist before some point in time, goes around in a loop in the middle, and then does not exist after some later point in time. Its existence is a closed circuit in space-time, not open ended paths.

What that means is the initial conditions before the non-chronal region cannot determine what happens. It's impossible to predict what will happen, not to mention all the paradoxes.

-Richard

publius
2009-Jul-26, 11:58 PM
Heh, this reminds of a crazy episode of "Futurama". Well, they're all crazy I guess, but in this, our heroes go back in time and of course, are the cause of the Roswell lore.

Fry encounters his grandfather, and discovers he's a bumbling accident prone idiot who is about to get himself killed. Fry's grandmother is a waitress, and he realizes they'll never get together unless he intervenes somehow (there's a hint that grandpa doesn't even like girls, which causes Fry some consternation).

Anyway, Fry ends up killing grandpa trying to save him. IIRC, he drives him out to some cabin the middle of nowhere, thinking nothing can hurt there. But the cabin turns out to be ground zero for an atomic bomb test. Fry is surpised he still exists. Well, he goes back to the diner, gets to talking with his grandmother, and well, Fry becomes his own grandfather...... (a literal play on that song, "I'm my own grandpa" )

The others had been carefully trying not to interfere with the time line, but after that they decided if the universe would allow that abomination, then it didn't care about anything and so the heck with it and they interfere the heck out of the timeline to get back home.

-Richard

Ken G
2009-Jul-27, 02:50 AM
My feeling in all this talk of paradox is that we are putting the cart before the horse. Time is a concept we invented to help us describe our experience, and that experience does not include time travel. So what we mean by "time travel" cannot be "move through time as we now know it", because we do that all the time and don't call it time travel. And if we ever found a way to move through time differently than our current experience, then it seems quite likely we are going to need a new concept of time.

This view is especially underscored by the discovery with relativity that in the most general situation, time does not precede dynamics, like the canvas precedes the painting, but rather time and dynamics appear together. Time doesn't tell us what kinds of dynamics are possible, we just observe what kinds of dynamics are possible and then try to retrofit some concept of time that will serve. Attempting to anticipate such a retrofitting process is fraught with difficulty.

Now I realize that we can say, "here's what we know about time thus far, so can we run with that and see how far it gets us in regard to time travel." But when we do that, and encounter a paradox, there's not much point in saying "so our theory tells us this is impossible", rather we should say "our theory clearly doesn't work to tell us if that is possible or not, because if it is possible, our theory must break down."

Put differently, if you get into something that calls itself a time machine, see someone who looks like a young you, and kill them, then you shouldn't expect to pop out of existence, or be stymied by some improbable intervention, you should expect to say "Oh, guess time wasn't what I thought it was." Kind of like the Futurama solution!

Or said another way, if the spacetime includes a closed timeline loop that is not guaranteed to be completely periodic (A -> B -> A), then what is the basis for calling it a closed timelike loop? It apparently isn't, there's something wrong with the global time coordinate-- that spacetime treatment was bogus, it contradicted itself, it messed up. That shouldn't surprise us-- if a runner is running on a circular track, they have a angular position "theta" at any time. If they are running at speed v at any instant, then dtheta/dt = v/R, for track radius R. So that formula maps t into theta, locally, and the runner can use theta instead of t. But it won't do it globally, because the runner's clock doesn't reset with each lap, but theta does. So we have a local mapping between theta and t, and if all we've ever experienced is the local physics of running on a track, we could easily not notice that t and theta are actually different things-- we could even build a global theory in which they are the same, and think all is well, as long as that global theory never finishes a lap. But then if we do think about a full lap, we don't say "it must be impossible to complete a lap", we say, "hey, theta wasn't the right concept of time after all, I guess I'm going to need a stopwatch."

So I'd say, either closed timelike loops are guaranteed to be periodic, or we have the wrong concept of time in their vicinity. So as soon as you travel back and see yourself, instead of be yourself, you know it has to be the latter. And if you did become your young self, that would more or less put an end to your wordline-- would it be immortal life, or early death?

DrRocket
2009-Jul-27, 03:56 AM
My feeling in all this talk of paradox is that we are putting the cart before the horse. Time is a concept we invented to help us describe our experience, and that experience does not include time travel. So what we mean by "time travel" cannot be "move through time as we now know it", because we do that all the time and don't call it time travel. And if we ever found a way to move through time differently than our current experience, then it seems quite likely we are going to need a new concept of time.


To speak precisely of time, or space, or anything else in physics we are forced to speak in the context of some theory.

The currently accepted theory, with good reason, is general relativity. I don't' think I would say that the treatment of time in general relativity is necessarily consistent with our current experience, since our current experience is consistent with Newtonian mechanics and the Galilean transformation. But relativity seem to be consistent with what has been measured experimentally and GR provides predictions of some phenomena involving space and time that are more consistent with experiment than are Newtonian constructs. Because of this agreement with a set of experimental data, and because there are no known inconsistencies with experimental data GR is accepted as our best available theory of space and time.

GR does predict some rather "weird" things. Black holes are among those "weird" things and they do not reflect "our experience". It is a perfectly valid question to ask whether closed time-like loops are permissible within the framework of general relativity, and in that context the existence or non-existence of such things is in no way contingent on any revision of the notion of time that comes with GR. One is then simply exploring the logical implications of the theory. The answer may cause one to conclude that nothing is unusual, that time behaves in ways not anticipated, or that the theory is inadequate and something different is needed. But before any such conclusions are drawn the logical implications of the model must be understood.

One can also pose the same question on the context of any theory that may compete with GR. The answer will then pertain to whatever concept of time is incorporated in that theory.

If one wants to discuss some non-standard version of "time" outside of GR and outside of any other known and formulated theory you can do that too. It may well be the case that we will eventually need a new concept of time, as radical or more radical than Einstein's concept of a curved space-time manifold, but without a clearly formulated alternative model, you are simply engaged in idle philosophy with no anchor in reality.

The issue of causality even with "time travel" need not involve any different concept of either time or space. It may simply involve the topology of space-time. I don't particularly believe that this is the case, but it is certainly not inconceivable. All that you would need is a topology that is not simply connected -- just put a handle on the glass and turn it into a mug.
That is not the only way, but it is a way. The point here is that the question of whether the geometry of space-time permits closed time-like loops is a valid question and it does not necessarily require the development of any new concept of "time".

This is not to say that a new and improved theory of space and time is undesirable. Quite the contrary. But it seems that every third physicist with a word processor is writing a book, speculating, but never bringing forth a consistent model or a testable prediction.

Ken G
2009-Jul-28, 03:59 AM
To speak precisely of time, or space, or anything else in physics we are forced to speak in the context of some theory.
Actually, that depends entirely on your definition of "precisely". If you mean "in accordance with a mathematical theory", then it is a tautological statement, you are talking about theoretical treatments of time and space, so of course will need a theory there. However, physics is not math, as I keep reminding you! Thus, we also have a perfectly good operational definition of the observable of time (based on clock readings), and we can certainly "speak about" it quite precisely, if one merely defines "precise" to mean "within a carefully limited observational uncertainty." I think there are a lot of experimentalists in this world, many with a healthy distrust of the imperatives of the various theories, who would take considerable umbrage at the suggestion that they cannot "speak precisely" about time, without having relativity in mind! The correct order of things is we build theories to explain observations, so the language of the theorist is first and foremost determined by the language of the experimenter.

(Indeed, one of the things I admire most about Feynman is that he virtually never started talking about any theory without first describing the experiment that gave that theory teeth. The basic language that the theory he is going to explain is going to use is thus always motivated in the language of some experimental outcome, and that is as it should be, lest we cavort with fooling ourselves.)

It is a perfectly valid question to ask whether closed time-like loops are permissible within the framework of general relativity, and in that context the existence or non-existence of such things is in no way contingent on any revision of the notion of time that comes with GR.Certainly, just as it is a perfectly valid question to ask whether arbritrarily fast velocities are permissible within the framework of Newtonian mechanics. This falls under the heading of knowing one's theory. But did we conclude therefore that velocities of arbitrary magnitude were physically possible, even though there was a limit to any velocity we'd ever seen? Not if we had half a clue. The history of science makes it pretty clear that deciding on what is possible based on your current best theory that unifies what you have already seen is an unreliable practice. It's not a sin to do it-- it's a sin to do it and not recognize its foibles.

Note this is quite a bit different from expecting an axiom of a theory to apply in new situations that seem similar to the ones that the theory has been shown to work for (and just what "similar" means is quite unclear, which is a large hole in the structure of physics but so be it). If relativity uses as an axiom that you cannot propagate information faster than light, then we can expect that to hold in a wide variety of situations (maybe even all, who knows), because it is an axiom of the theory. It is part of the structure of the theory, if it weren't true we'd have no reason to expect the theory to work at all. It's kind of a "core value" of the theory, which gives us the right to expect it to extrapolate. But we are never that surprised when it turns out not to extrapolate absolutely everywhere, the history of science shows that quite clearly. We just don't know how far we can push the theory until it breaks-- and time travel is quite a push.


One is then simply exploring the logical implications of the theory. Certainly. But you are talking about something different-- you are talking about what it tells us about the theory. It's fine to "know thy theory", for those who are curious about the theory. For those who are curious about reality, the problem is, what the theory says doesn't tell us anything about the reality, if we have no prior basis to expect the theory to apply to that reality. Again, what such a "prior basis" looks like is not clearly defined, which is a big problem for science. But history is the best guide we have there, and history is dotted with plenty of both in the way of successful extrapolations, and dismal failures to extrapolate. Which one is time travel? One only has one's own personal opinion, and I'm saying, I can hardly see a case of a phenomenon that would be likely to be a "dismal failure of extrapolation" than time travel, since anything that could properly be termed time travel would challenge the foundations of the very methods of physics (as a science involving the prediction of the future from the past, or more correctly, the prediction of the past before it happened).


It may well be the case that we will eventually need a new concept of time, as radical or more radical than Einstein's concept of a curved space-time manifold, but without a clearly formulated alternative model, you are simply engaged in idle philosophy with no anchor in reality. And I'm saying that is exactly what one is doing if one applies general relativity to time travel, just as one was doing that when applying Greek concepts of gravity to the solar system, or Galilean concepts to very fast speeds, or Newtonian concepts to an atom, or phlogiston concepts to thermodynamics.

But I agree with you that contemplating conservation of energy allowed us to anticipate the neutrino, and various other particles were anticipated by symmetry principles of various other kinds, so this is a very difficult question indeed-- when is physics physics, and when is it idle philosophy? I say that there's no harm in contemplating what GR says about time travel, but if you want that to mean something in the real world, you have to ask yourself one simple question: do you feel lucky?


The point here is that the question of whether the geometry of space-time permits closed time-like loops is a valid question and it does not necessarily require the development of any new concept of "time".I agree, which is why I never said that the question requires a new concept of time, as questions never do that. I said the discovery of time travel probably would. So what good is applying a theory that, if it was ever needed in some context (like time travel), likely wouldn't even work for it? And all this seems true to me even if we had unified GR and QM. In the absence of that, we're really just guessing about time travel. Indeed, I believe you tried to make that exact same point earlier in the thread, in regard to my claims that A -> B -> A causality violates no current principles of physics.

DrRocket
2009-Jul-28, 05:02 AM
I think there are a lot of experimentalists in this world, many with a healthy distrust of the imperatives of the various theories, who would take considerable umbrage at the suggestion that they cannot "speak precisely" about time, without having relativity in mind! The correct order of things is we build theories to explain observations, so the language of the theorist is first and foremost determined by the language of the experimenter.


That may once have been true. It might even be the way things ought to be in a more nearly perfect world. But with modern theories, general relativity in particular we have come to and gone beyond a critical fork in the road.

The experimenter is forced to deal with those things that are measurable within the constraints of available technology and his ingenuity (which has been shown to be considerable).

To measure time he is forced to use clocks that are available to him, while general relativity has demonstrated that time is local. That means that from a purist perspective the clock on the wall of the laboratory, being spatially separated from the clock on the bench, is not necessarily measuring the same thing. The approximation involved is sufficiently close, for most purposes, that the experimenter may be safe in considering the two clocks to be twins (but for purposes of, say, the Pound-Rebka experiment this may not be an adequate approximation). In short, the experimenter is forced to conduct many experiments as though he were operating in the tangent space, while the language of the theorist applies to the curved manifold of space-time.

Thus the language of the experimenter and of the theorist are not one in the same, and the language of the theorist is not driven solely by the language of the experimenter. There is an imperfect dictionary relating the two.

In the case of the issue of time travel or closed time-like loops the situation is exacerbated. What it quite clear is that there are no recognized examples of time travel. There are no reasonable experiments that might be performed with any reasonable expectation of time travel in any available laboratory, at least within that which has been imagined and communicated by the experimental community so far as I am aware. The situations in which closed time-like loops might and be consistent with any accepted theory are in extreme conditions, such as inside the event horizon of a Kerr black hole. We lack, at least at the present, any concept of an experiment that might be carried out to investigate such phenomena. Certainly any laboratory demonstration of a closed time-like loop would guarantee a first-class, all-expenses-paid trip to Stockholm.

Lacking any experimental avenue we are forced to consider the implications and limitations of available theories. In short we can investigate the logical implications of the mathematical model that we call general relativity, or we can investigate any other viable mathematical model (the only one of which I am aware is Einstein-Cartan theory). The extreme conditions involved in the relevant circumstances under which those models predict closed time-like curves is such that the ordinary language of the experimentalist working in the tangent space is simply not applicable. As you have remarked yourself, time in that context has no clear meaning aside from the results of integration along a world line. Since we have no way to even attempt to examine the results of the movement of a clock along a world line that lies on the far side of an event horizon, we are left with the language of the theorist, and only the language of the theorist.

So we have two alternatives. We can limit that which we call physics to only those phenomena that are amenable to experiment within a reasonable time frame. Or we can utilize theoretical models, subject them to those experiments that can be performed within the available instrumentality and ingenuity, continuing to test them, question them to the extent practicable, and then utilize the surviving mathematical models to attempt to determine the physics of extreme situations beyond our experimental capability -- which may be forever beyond our capability.

This may not be totally satisfactory. But I think it is the best that we are likely to attain. There is some potential benefit.

If all closed time-like curves exist beyond event horizons, then it is quite possible that the existence or non-existence is irrelevant to anything that happens on our side of the horizon. In that case a reasonable response is "Who cares". On the other hand, there are true logical paradoxes that come along with closed time-like curves. These might be resolved by finding that no action along such curves actually results in a contradiction or it may be resolved by finding that a theory competing with GR does not permit such loops but is otherwise comparable with GR in explaining gravity. Thus the pursuit of such questions may lead one to accept one model and reject another, solely on the bais of phenomena that are not amenable to experiment. In either case the issue must perforce be discussed in the abstract language of the theorist, since the more concrete language of the experimenter simply does not apply.

When you think about it, experimenters are limited by time and available resources to address only a very small number of possible physical scenarios. Theories, on the other hand, in principle address all possible physical scenarios. It is a perfectly reasonable position therefore, to view experiments as having the function of testing and possibly refuting theories, while the role of theories is to represent the totality of our understanding of nature. From that perspective it is the language of the theorist that is most universal and therefore most applicable.

Thus, it is not a given that the theorist is subservient to the experimentalist, nor the other way around. It is a matter of (gasp) philosophy. Or in other words it is not a useful question. We need both, and neither has the right to call the tune.

It is useful to the experimenter to think that his experiments are paramount. It helps to motivate him and to work to make sure that his experiments are as accurate, understandable and defendable as possible.

It is useful to the theorist to think that his theories are paramount. It helps to motivate him and to formulate theories that are clear, that predict nature accurately, and that have wide applicability.

The theorist and the experimentalist must play nice. They need each other.



Now to deal with your crack regarding mathematics.

Ultimately, Feynman (The Character of Physical Law) put his finger on the crux: "To summarize , I would use the words of Jeans, who said that Ďthe Great Architect seems to be a mathematicianí ".

So, as you say, physics is not mathematics. But it wants to be like its big brother when it grows up. :)

publius
2009-Jul-28, 05:47 AM
This reminds me of Dr. Ron Mallet, who is sort of obssesed with time travel. He had an idea that he could a tiny region with CTLCs just big enough to see if anything funny happened to some neutrons. Although the energy requirements were still huge, he thought he could amplify the frame dragging effect of a circulating beam of light by "slowing it to a crawl" using a Bose-Einstein condensate (or whatever it is in the famous slow light to the speed of an ant experiments).

However, I think he's conceded himself that that won't work as he first thought, but he continues to plug away at the idea of creating CTLCs in the lab.

And that brings up a question which I think I've brought up before, but Dr. Rocket wasn't here then.

Suppose you are a Power That Be (president, other high official, etc), and it comes to your attention that the someone like Mallet has stumbled onto something that just might work. There is a possibility that CTLCs will be created.

What do you do? Do you allow it to go forward, or do you stop it in its tracks?

-Richard

DrRocket
2009-Jul-28, 06:40 AM
This reminds me of Dr. Ron Mallet, who is sort of obssesed with time travel. He had an idea that he could a tiny region with CTLCs just big enough to see if anything funny happened to some neutrons. Although the energy requirements were still huge, he thought he could amplify the frame dragging effect of a circulating beam of light by "slowing it to a crawl" using a Bose-Einstein condensate (or whatever it is in the famous slow light to the speed of an ant experiments).

However, I think he's conceded himself that that won't work as he first thought, but he continues to plug away at the idea of creating CTLCs in the lab.

And that brings up a question which I think I've brought up before, but Dr. Rocket wasn't here then.

Suppose you are a Power That Be (president, other high official, etc), and it comes to your attention that the someone like Mallet has stumbled onto something that just might work. There is a possibility that CTLCs will be created.

What do you do? Do you allow it to go forward, or do you stop it in its tracks?

-Richard

Mallett is still "kind of hung up" He is still trying to get somebody to fund one his experiments. I think he needs a rich nut. But he may have found one. He is hooked up with Spike Lee, with some project involving his life story as a minority theoretical physicist who has "discovered the basic equations for a working time machine".

http://www.phys.uconn.edu/~mallett/main/aspikeleefilm.htm


http://www.phys.uconn.edu/~mallett/main/main.htm

If I am me, and a "Power That Be" I let him do his thing (but I don't fund him because I know that this is not gong to work). He doesn't have any decent theory to back him up and his experimental set up on his desk top is not likely to even put a dent in the UConn power bill. This has all the earmarks of another "cold fusion" without the initial experimental data. I know some of the guys who got sucked into that tar baby, by just being at the wrong place at the wrong time -- fortunately they came out unscathed.

If I am a usual "Power That Be", and am clueless with regard to the underlying science (I know quite a few "powers that be"), then I still don't fund him because it just plain sounds wacko and I am protecting my behind against the "golden fleece award". This still smells like another "cold fusion" and I am not going to be known as the guy who gave it it's start. But I do commission some people who do know what they are doing to quietly look at this thing and report back, and I fund them. If he files a patent application I slap a secrecy order on it and tie him up so bad that he can't even tell his kids what he did, just in case.
[/URL]
But there is no danger. H.G. Wells did not write physics books. He can spin light in tight little circles all that he wants and he is not going to get a time machine. Some estimates involve a circle somewhat larger in diameter than the observable universe, so he may have trouble finding a lab with adequate floor space. Other calculations indicate that he is just plain out to lunch.

[URL="http://en.wikipedia.org/wiki/Ronald_Mallett"]http://en.wikipedia.org/wiki/Ronald_Mallett (http://en.wikipedia.org/wiki/Ronald_Mallett)

please
2009-Jul-28, 07:03 AM
So as soon as you travel back and see yourself, instead of be yourself...doesn't that alone mean that, at that point, these two yourselves already exist as separate entities in locally SRT-compatible space-time region (since you are now outside of, and away from, the wormhole or whatever had brought you back in time),
and there kinda should be no reason for anything that happens to one of them to affect another one, except than in STL manner, as our known physical laws prescribe?


Suppose you are a Power That Be (president, other high official, etc), and it comes to your attention that the someone like Mallet has stumbled onto something that just might work. There is a possibility that CTLCs will be created.

What do you do? Do you allow it to go forward, or do you stop it in its tracks?That's comparable to stem cell research or, in fact, whole lot of other smaller issues. In theory, that should be none of your business - just keep building roads and chase serial killers. But no, people constantly come up with better ways to spend our taxes, and some of those have quite bad side effects of hindering harmless developments. Of course, stem cell research can be employed to unethical or dangerous purposes, but so can nuclear research be - shall we now send nuclear scientists to work on agriculture instead? I mean, USA clearly think it's not that bad idea for Iran, so maybe they should do the same in USA too.

Xtrozero
2009-Jul-28, 07:17 AM
I would find that FTL communications would not only be possible but we will be FTL communications capable long before we would ever need it.

With the Einstein/Podolsky-Rosen phenomenon we could influence a photon to create communication as another photon is curiously influenced the same way at apparently the same time no matter the distance

DrRocket
2009-Jul-28, 07:39 AM
With the Einstein/Podolsky-Rosen phenomenon we could influence a photon to create communication as another photon is curiously influenced the same way at apparently the same time no matter the distance

And how do you do that ?

No one else has managed to devise a means to transmit information in that manner. And that is why there is no uproar over a violation of the special theory of relativity or causality.

If you can do what you say, then demonstrate it and prepare for a trip to Stockholm.

please
2009-Jul-28, 07:54 AM
...and prepare for a trip to Stockholm.I think they wait their Stockholm trip for years after their discoveries... plenty of time to prepare for that.

please
2009-Jul-28, 08:06 AM
a bit of off topic here

nazis has won the WW2 in europe. then american scientists focused their efforts on time machine project instead of atomic bomb, and specially trained american soldiers were sent few years back in time to change the history, before it was too late. their mission was a success, however, that erased the time machine project along with nazis victory, and made the history look like we know it today. and you know it because one of those soldiers, the only survivor, told you so before he died yesterday...

imagine this story (the last part, at least) really happened to you, would you believe the soldier? I mean, occam razor tells us we could explain this event by assuming he was just one old crazy man, however, what could possibly make you believe him?

Ken G
2009-Jul-28, 03:30 PM
Thus the language of the experimenter and of the theorist are not one in the same, and the language of the theorist is not driven solely by the language of the experimenter. There is an imperfect dictionary relating the two.Yes, I would accept that characterization a whole lot more readily than your above statement that we need theory to speak of anything in physics.


Thus, it is not a given that the theorist is subservient to the experimentalist, nor the other way around. It is a matter of (gasp) philosophy. Or in other words it is not a useful question. We need both, and neither has the right to call the tune. We do need both, in synergy. I'm just saying that the experimenter language never turns out to be wrong later on because it is necessarily restricted to experiments that have actually happened, whereas the theorist is often wrong, especially when extrapolated beyond said experimental support. Just what constitutes "extrapolation" versus "application" if a very difficult question in science, so much so that we have little choice than to just "wing it". But we should know we are winging it.

Ultimately, Feynman (The Character of Physical Law) put his finger on the crux: "To summarize , I would use the words of Jeans, who said that ‘the Great Architect seems to be a mathematician’ ".

So, as you say, physics is not mathematics. But it wants to be like its big brother when it grows up. Actually, I rarely say this, but Feynman is quite clearly wrong in that statement, if "seems to" is to be interpreted as "is" (if we use "seems to", then we must say seems to to whom). The experience of life itself is so paramountly clear on that point, only a theoretical physicist could ever make that remark! It's a clear case of "when all you have is a hammer, everything looks like a nail." All we can say, logically, is that mathematics affords us tremondous predictive power in situations that conform well to mathematical idealization, and which may in turn extend in principle to everything else, but certanly not in practice, and the extensions are purely unestablished assumptions. That's just a fact-- saying any more is (gasp) pure philosophy, and it is the personal philosophy of a theoretical physicist. Which is fine, if we recognize that.

This is similar to the reason I just laugh when Weinberg, another theoretical phycisist of the highest order, makes statements along the lines that all anyone needs is theoretical physics because it is the only valid path to truth. For whom? Most people have no chance of understanding any two words put together in theoretical physics, yet their experience of life is every bit as rich and challenging and tragic and triumphant as Weinberg's, in their own way. When Weinberg is facing a person crisis, shall he whip out some equations to navigate his path?

DrRocket
2009-Jul-28, 05:13 PM
That's just a fact-- saying any more is (gasp) pure philosophy, and it is the personal philosophy of a theoretical physicist. Which is fine, if we recognize that.


Of course Feynman's statement represents the personal philosophy of a theoretical physicist. I think most people would recognize that.

It doesn't hurt much that the philosophy espoused has resulted in the development of physical laws with astounding predictive power. In that sense it appears that he is correct.

The clarity of that philosophy stands in stark contrast to the obfuscations of professional philosophers. Feynman was a much clearer thinker and better philosopher than those who usually describe themselves as "philosophers". So is Weinberg. So is Chester.

Ken G
2009-Jul-28, 07:12 PM
Of course Feynman's statement represents the personal philosophy of a theoretical physicist. I think most people would recognize that.

It doesn't hurt much that the philosophy espoused has resulted in the development of physical laws with astounding predictive power. In that sense it appears that he is correct.
The extent to which your second paragraph contradicts your first is exactly what I am talking about. The demonstration of astounding predictive power does not serve to support the idea that the "creator was a mathematician," which is the meaning you take from it (of course, the literal meaning that the creator seems like a mathematician to a theoretical physicist is saying something very different from your meaning-- everything seems like reflections of our own selves). A musician sees plenty to make the creator "seem like" a composer, the painter thinks the creator "seems like" an artist, the comedian sees the wry and sardonic sense of humor. We see what we want to see, it is the classic fallacy of "drawing a conclusion from only one side of the story." The other sides? All the rest of existence, the vast majority of which stands in stark contrast to any suggestion that the creator was a mathematician.

If we are talking pure personal philosophy, as you say in your first paragraph, then it seems to me that "the creator", whatever that concept is intended to convey, would be rather puzzled by the entire endeavor of mathematics, and would look on it sort of the way we currently look at a bee dance. There seems to be some point to it, but the language is very alien.

The basic point is, just noticing that reality submits to analysis via a certain approach, does little to establish that reality "really uses" that approach to function. I believe this is what Einstein also meant, in his famous watch analogy. Furthermore, the history of science is a very long tale of scientists believing that they had some kind of handle on what reality was "really doing". The successes of science have been spectacular, and the only time its failures are equally spectacular is whenever scientists fell into that particular mode of thought.

In summary, imagining that mathematics is the "big brother" to physics is a completely wrong picture. Mathematics and physics are both little brothers, the difference being, physics has a really big brother to appeal to when it gets in a jam-- reality.
Feynman was a much clearer thinker and better philosopher than those who usually describe themselves as "philosophers". So is Weinberg.I like Feynman's philosophy too, but he knew little about real philosophy. What I've seen of Weinberg's philosophy, which admittedly isn't much, borders on childishly oversimplified. There have been many professional philosophers who were just as brilliant as Feynman and Weinberg, and in many cases better masters of logic and language. Arguments from ignorance are not terribly compelling, and I've never seen either Feynman or Weinberg make an authoritatively insightful analysis of any professional philosophy, other than to make remarks that actually boil down to nothing more than "it isn't physics."

DrRocket
2009-Jul-28, 07:44 PM
I've never seen either Feynman or Weinberg make an authoritatively insightful analysis of any professional philosophy, other than to make remarks that actually boil down to nothing more than "it isn't physics."


http://physicshead.blogspot.com/2008/03/feynman-philosophy-is-bull****.html

You will have to fill in the stars to get to the site.

Ken G
2009-Jul-28, 07:48 PM
That link appears to be dead.

please
2009-Jul-28, 07:50 PM
lol :D
try http://physicshead.blogspot.com/2008/03/feynman-philosophy-is-bullsh%69t.html

grant hutchison
2009-Jul-28, 07:55 PM
That link appears to be dead.A victim of the forum nanny software. You need to replace the asterisks in DrRocket's URL with the obvious four-letter word.
The result is to find Feynman at his least insightful.

Grant Hutchison

Ken G
2009-Jul-28, 10:11 PM
OK, thanks, I found it. Interesting page about Feynman, lots of nice quotes. Yes, that one is not terribly insightful-- and to realize how not-insightful it was, just imagine it was said by someone without his rep.

DrRocket
2009-Jul-28, 10:36 PM
OK, thanks, I found it. Interesting page about Feynman, lots of nice quotes. Yes, that one is not terribly insightful-- and to realize how not-insightful it was, just imagine it was said by someone without his rep.

That statement made by someone else might raise the hackles of political correctness, but that has nothing whatever to do with insight.

His point is quite simple. During the same era there were people doing work, that in Feynman's opinion, was of much greater iimportance and which provided much deeper insight into nature. Since one has only a finite amount of time on this earth one must apportion one's time to those things that one judge's most likely to be fruitful. Newton and Harvey made Feynman's cut. Spinoza did not, for the reasons stated. I happen to agree with Feynman.

If you feel that Spinoza is beneficial to your objectives, then you are fully justified in studying his works in detail. That is a valid position. The opposite position is also valid.

If these axioms are helpful to you then that is just wonderful. http://frank.mtsu.edu/~rbombard/RB/Spinoza/ethica5.html

I personally find other axioms to be more useful. But use whatever works for you (an empiricist version of rationalism).

grant hutchison
2009-Jul-28, 10:57 PM
His point is quite simple.While entirely agreeing with your thoughts on how we each should choose to spend our time, and while being grateful that Feynman spent his time in physics rather than philosophy, I feel compelled to point out the following.

Feynman's objection to Spinoza distils down to exactly what Ken said: "It isn't physics."
He dismisses Spinoza because he can't think of a way to test whether Spinoza is right or not! Well, duh. That particular quote would have been better run under the title: "Feynman makes a rookie category error." (Then the URL would be easier to post, too. :lol:)

Grant Hutchison

DrRocket
2009-Jul-28, 11:11 PM
While entirely agreeing with your thoughts on how we each should choose to spend our time, and while being grateful that Feynman spent his time in physics rather than philosophy, I feel compelled to point out the following.

Feynman's objection to Spinoza distils down to exactly what Ken said: "It isn't physics."
He dismisses Spinoza because he can't think of a way to test whether Spinoza is right or not! Well, duh. That particular quote would have been better run under the title: "Feynman makes a rookie category error." (Then the URL would be easier to post, too. :lol:)

Grant Hutchison

A statement does not need to be physics to be testable. Statements made by economists are often tested observationally -- and are often wrong. Statements made by drug manufacturer's are tested by experiment involving statistical analysis. Statements made by politicians are tested in the light of eventual actions -- and are often found to be wrong or vacuous. Statements made by philosophers can be tested, as Feynman notes, by evaluating whether there is any sensible difference between affirmation and negation.

Feynman did not say that he could not figure out how to tell if Spinoza is right or wrong. He said that there is no significance to the question of whether Spinoza is right or wrong.

Philosophers debated for years the question of how many angels can dance on the head of a pin. The issue there is not whether the guy who says "12" is right or wrong, but rather the utter meaninglessness of the question.

One is reminded of a portion of Asimov's Foundation Trilogy in which a logician takes a speech by a politician, reduces it to symbolic logic, and finds that it all cancels. That is an extreme example of evaluation of a proposition without need to resort to physics.

You are of course correct in saying that another title would have made the URL easier to handle.

Xtrozero
2009-Jul-28, 11:13 PM
And how do you do that ?

No one else has managed to devise a means to transmit information in that manner. And that is why there is no uproar over a violation of the special theory of relativity or causality.

If you can do what you say, then demonstrate it and prepare for a trip to Stockholm.

I'm not saying we have the means just yet to do this, but my point is based in the fundamentals of the Einstein/Podolsky-Rosen phenomenon in that the two photons are connected thus making distance a moot point. If you influence one then the other one is influenced the same way at the same time. This seems to be faster than light speed, but if they are subatomicly attached and act as one at any distance then there is no need for anything to travel. so letís say they are one light year apart then they would act as if they were one partical one light year long and a photon wide.

So if I had a stick that was 10 miles long and pushing down on one end was a "0" and pulling up was a "1" would I not have instant communication since moving one end instantly moved the other too?....now lets say I have two photons that acted like a one light year long stick...get the point.

In any case communication would be possible.

grant hutchison
2009-Jul-28, 11:29 PM
Feynman did not say that he could not figure out how to tell if Spinoza is right or wrong. He said that there is no significance to the question of whether Spinoza is right or wrong.I'm afraid I didn't catch him saying that, in the quote provided. :)


Philosophers debated for years the question of how many angels can dance on the head of a pin. The issue there is not whether the guy who says "12" is right or wrong, but rather the utter meaninglessness of the question.I think those were theologists. And I think they were also imaginary theologists, since there seems to be no evidence that any such debate ever took place, except in the minds of writers who condemned the imaginary practice in retrospect.

Grant Hutchison

DrRocket
2009-Jul-28, 11:36 PM
I'm afraid I didn't catch him saying that, in the quote provided. :)

That is how I take the sentence, " You can take every one of Spinoza's propositions, and take the contrary propositions, and look at the world and you can't tell which is right."

grant hutchison
2009-Jul-28, 11:55 PM
That is how I take the sentence, " You can take every one of Spinoza's propositions, and take the contrary propositions, and look at the world and you can't tell which is right."Which seems to me to be a pretty clear statement to the effect that, "I [rhetorical you] can't think of a way to test whether Spinoza is right or wrong."
Now, one can gloss that, as you did, by adding an inference that this failure robs Spinoza's statements of all significance. (And I'm pretty sure that's exactly what Feynman thought we'd take from the statement. :)) The assumption we're all meant to make, then, is that only propositions testable in the world can hold significance.
And that's the category error. It misses pretty much the whole point of philosophical discourse.

Grant Hutchison

George
2009-Jul-29, 01:29 AM
Which seems to me to be a pretty clear statement to the effect that, "I [rhetorical you] can't think of a way to test whether Spinoza is right or wrong."
Now, one can gloss that, as you did, by adding an inference that this failure robs Spinoza's statements of all significance. (And I'm pretty sure that's exactly what Feynman thought we'd take from the statement. :)) The assumption we're all meant to make, then, is that only propositions testable in the world can hold significance.
And that's the category error. It misses pretty much the whole point of philosophical discourse.
A great example of how a person's strength can often be a weakness. And those that have the greater weaknesses, are often those with the greater strengths.

DrRocket
2009-Jul-29, 02:45 AM
Which seems to me to be a pretty clear statement to the effect that, "I [rhetorical you] can't think of a way to test whether Spinoza is right or wrong."
Now, one can gloss that, as you did, by adding an inference that this failure robs Spinoza's statements of all significance. (And I'm pretty sure that's exactly what Feynman thought we'd take from the statement. :)) The assumption we're all meant to make, then, is that only propositions testable in the world can hold significance.
And that's the category error. It misses pretty much the whole point of philosophical discourse.

Grant Hutchison

My interpretation is still a bit different.

To me what Feynman is saying is that Spinoza's assertions are so vacuous that neither their truth nor falsity has any impact on anything that affects any item of interest to Feynman.

It seems to me that "testable in the world" includes not only physical tests, but also tests of logic, and tests involving thought experiments (as might be applicable to moral or ethical questions as well as physical issues). If the point of philosophical discourse is such that tests of this nature are inapplicable, then I guess I don't see the point either. In other words if a statement is such that I don't care whether it is true or false, that statement might just as well not be made. For instance, I don't care if 12 angels can dance on the head of a pin.

Frankly, I find Spinoza's 42 axioms (see link in earlier post) rather vacuous.

Ken G
2009-Jul-29, 04:17 AM
Feynman's objection to Spinoza distils down to exactly what Ken said: "It isn't physics."
He dismisses Spinoza because he can't think of a way to test whether Spinoza is right or not! Well, duh. That particular quote would have been better run under the title: "Feynman makes a rookie category error."
That was my reaction as well, to a tee.

Ken G
2009-Jul-29, 04:34 AM
To me what Feynman is saying is that Spinoza's assertions are so vacuous that neither their truth nor falsity has any impact on anything that affects any item of interest to Feynman.
And this is the heart of the matter. Feynman is welcome to adopt a personal philosophy that all philosophy is of no significance to him because it cannot be tested. And of course, he cannot test his own philosophy on the matter either. But overlooking that core inconsistency, we still have the issue of whether Feynman is speaking for himself, versus claiming to be speaking an absolute truth. Even in your own remarks above, you seem to be going back and forth as to which way you would frame the intended impact of his statements. We can all agree that if he is choosing to espouse a personal philosophy about the importance of empirical testability, then he should feel welcome to do so. However, he, and you, should probably be made aware that philosophers have also done so, and more exhaustively, because empiricism is itself a philosophical camp-- just not Spinoza's.

By the way, we should probably enter into the record some of the most basic claims Spinoza was making. From the Stanford encyclopedia of philosophy, Spinoza had this to say on the concept of god:
"God is the infinite, necessarily existing (that is, uncaused), unique substance of the universe. There is only one substance in the universe; it is God; and everything else that is, is in God."

Now, only a fool would expect that statement to be objectively testable, and Feynman is no fool, so obviously the disconnect is at a more axiomatic level. But ironically, that statement reminds me an awful lot of someone who looks for laws saying something like "God is in the laws", or one who applies mathematics to the understanding of reality saying "the creator seems to be a mathematician." Whatever Feynman and his son were laughing about, my chuckle comes from that irony.
In other words if a statement is such that I don't care whether it is true or false, that statement might just as well not be made. Again, we must ask the fateful question: are you simply asserting a personal philosophy here, or are you making some claim on truth? And if you don't care what Spinoza's take was on that issue, why should anyone else care about yours? (I'm not saying no one should, I'm saying your statement reveals a core inconsistency in how you really feel about philosophy, versus how you frame the topic.)

DrRocket
2009-Jul-29, 07:00 AM
And if you don't care what Spinoza's take was on that issue, why should anyone else care about yours? (I'm not saying no one should, I'm saying your statement reveals a core inconsistency in how you really feel about philosophy, versus how you frame the topic.)

Anyone is free to formulate their own philosophy any way they choose. No one should particularly care about anyone else's philosophy except perhaps as raw material for formulating their own.

I don't care if they accept mine, formulate their own, or get a lobotomy and adopt no philosophy at all.

I have never said that I hold philosophy in low esteem. I simply hold those who claim to be "philosophers" in low esteem. There is a difference. That also is a personal decision and a personal choice. It is based solely on my assessment of the worth of the work of such individuals. I have seen more cogent thought and more worthwhile philosophy from real, no-kidding cowboys, than from professional philosophers. I have never heard a cowboy who was unsure as to whether or not his horse exists.

If Spinoza works for you that is just fine with me. But just as it is my personal decision that his work holds no value to me, a contrary decision is equally as arbitrary. That is the nature of philosophy. It has no absolute value and no absolute truth.

Statements to the effect that Feynman "doesn't get it" or that his statements "lack insight" are also completely arbitrary. Feynman gets it quite well -- from his perspective which is just as valid as any other perspective with respect to untestable assertions. And anyone who claims that Feynman "lacks insight" on the basis that his perception disagrees with theirs on such matters, is lacking in insight themselves. There is nothing more ridiculous than asserting absolute truth or value with respect to the philosophy of philosophy.

slang
2009-Jul-29, 07:45 AM
So if I had a stick that was 10 miles long and pushing down on one end was a "0" and pulling up was a "1" would I not have instant communication since moving one end instantly moved the other too?

No. You push one end of the stick. That force is propagated through the stick, molecule by molecule. One of the physics people here can explain in detail perhaps, but the point is, it's a process that takes time. It is not instant.

publius
2009-Jul-29, 08:00 AM
[/URL]
But there is no danger. H.G. Wells did not write physics books. He can spin light in tight little circles all that he wants and he is not going to get a time machine. Some estimates involve a circle somewhat larger in diameter than the observable universe, so he may have trouble finding a lab with adequate floor space. Other calculations indicate that he is just plain out to lunch.

[URL="http://en.wikipedia.org/wiki/Ronald_Mallett"]http://en.wikipedia.org/wiki/Ronald_Mallett (http://en.wikipedia.org/wiki/Ronald_Mallett)

Ah, but let's don't worry about Mallet's ideas. Let's suppose that someone figures out something that is plausible. That is, the experts think it might work, or they're divided, some thinking it might work and others not. Do we allow such an experiment that might create CTLCs in the lab to go forward?

On the one had, I'd want very badly to know what would happen, yet very afraid of would happen. I think the latter would trump the former.

-Richard

grant hutchison
2009-Jul-29, 08:32 AM
If Spinoza works for you that is just fine with me. But just as it is my personal decision that his work holds no value to me, a contrary decision is equally as arbitrary. That is the nature of philosophy. It has no absolute value and no absolute truth.For that last statement to have much coherence, you'd need to define "absolute value" and "absolute truth". These definitions will be propositions untestable in the world, since they deal with the stuff of thought. In trying to articulate why you reject Spinoza, then, you're using propositions of the kind Feynman dismisses Spinoza for using.

Grant Hutchison

please
2009-Jul-29, 12:05 PM
Spinoza has been dead for last 300 years, can we all move along now...

grant hutchison
2009-Jul-29, 12:30 PM
Spinoza has been dead for last 300 years, can we all move along now...Apparently not. :lol:
Apologies for the hijack.

Grant Hutchison

DrRocket
2009-Jul-29, 04:15 PM
For that last statement to have much coherence, you'd need to define "absolute value" and "absolute truth". These definitions will be propositions untestable in the world, since they deal with the stuff of thought. In trying to articulate why you reject Spinoza, then, you're using propositions of the kind Feynman dismisses Spinoza for using.

Grant Hutchison

For clarification an absolute truth or and absolute value as used in my statement is one that is testable in the world -- a statement that can be confirmed or refuted by means of a physical or logical test that relates to a phenomena with a determinable impact on oneself.

That statement has no bearing on why I ignore Spinoza. Note that I do not reject Spinoza, I simply find him irrelevant. There is a difference. My position is based on his work, for instance the fact that I find his axioms (see link to axioms in earlier post) vacuous.

That is testable. I do find the axioms vacuous. And since this is a personal decision, that is all the test required.

If you don't like my tests or my conclusions, then you are free to accept Spinoza for your personal philosophy. That is the importance of the value and truths of philosophy not being abolute and not being testable in an objective laboratory.

DrRocket
2009-Jul-29, 04:19 PM
I'm not saying we have the means just yet to do this, but my point is based in the fundamentals of the Einstein/Podolsky-Rosen phenomenon in that the two photons are connected thus making distance a moot point. If you influence one then the other one is influenced the same way at the same time. This seems to be faster than light speed, but if they are subatomicly attached and act as one at any distance then there is no need for anything to travel. so let’s say they are one light year apart then they would act as if they were one partical one light year long and a photon wide.

So if I had a stick that was 10 miles long and pushing down on one end was a "0" and pulling up was a "1" would I not have instant communication since moving one end instantly moved the other too?....now lets say I have two photons that acted like a one light year long stick...get the point.

In any case communication would be possible.

The EPR expereiment does not violate causality or special relativity because entanglement does not permit one to send an information-carrying superluminally. All that happens is that experiments at distant locations are correlated.

Neither does your stick example provide a contradiction to special relativity. What it does do is show why rigid bodies are not an allowable idealization in special relativity. There are other, more subtle, thought experiments that also show that rigid bodies are not allowed in SR, but the example that you chose is one that is used quite often to make that point.

In a real stick the movement of one end sends a stress wave to the other end at a speed that is very close to the speed of sound. It is that stress wave that results in displacement of the far end. The transmission is quite a bit slower than light speed.

Argos
2009-Jul-29, 04:44 PM
No. You push one end of the stick. That force is propagated through the stick, molecule by molecule. One of the physics people here can explain in detail perhaps, but the point is, it's a process that takes time. It is not instant.

The force propagates at the speed of the sound in the material. Simple as that.

DrRocket
2009-Jul-29, 04:52 PM
Ah, but let's don't worry about Mallet's ideas. Let's suppose that someone figures out something that is plausible. That is, the experts think it might work, or they're divided, some thinking it might work and others not. Do we allow such an experiment that might create CTLCs in the lab to go forward?

On the one had, I'd want very badly to know what would happen, yet very afraid of would happen. I think the latter would trump the former.

-Richard

I would do pretty much what I said in my post, independent of who's notion it is. The experiment will definitely occur.

If the proposal is more credible that Mallet, I still let it go forward. If I don't somebody else will, and that is an uncontrolled situation. But the experiment might carred out as a "black operation", depending on the nature of the experiment and the specific experimenter. If possible I co-opt the researcher and have him carry out the experiment in a "black facility", and I definitely put a team on the job to perform the experiment, even as a replication, in such a facility.

The results of the experiment may never see the open literature. And if the experiment yields positive results there is zero chance of a patent being issued -- an airtight secrecy order will definitely be issued. (In case you have never heard of a secrecy order -- the military reviews patent applications and can issue such orders which prevent the publication of a patent and bind the inventor with regard to talking about the invention. In essence they can make the patent material classified, depending on the nature of the specific secrecy order.)

This thing has potential as a weapon. So the inventor is subject to ITAR. I make him very aware of this. He is very cooperative since he does not want to live in a cell.

And since the result of this experiment is a time machine,if it works I can use it and hinsight to go back and clean up any mistakes or leaks.

please
2009-Jul-29, 04:54 PM
I do not reject Spinoza, I simply find him irrelevant. There is a difference. My position is based on his work, for instance the fact that I find his axioms (see link to axioms in earlier post) vacuous.Well he's relevant if you are looking for relevance. For example, I find "From a given definite cause an effect necessarily follows; and, on the other hand, if no definite cause be granted, it is impossible that an effect can follow (http://frank.mtsu.edu/~rbombard/RB/Spinoza/ethica1.html#Axioms)" axiom very relevant to this thread - it lets me know that if I could ask my question to Spinoza, he would basically agree with me (because he had nothing to back causality up, hence it is given as an axiom). For another example, "One substance cannot be produced by another substance (http://frank.mtsu.edu/~rbombard/RB/Spinoza/ethica1.html#Prop.%20VI.)" could be very relevant to conservation laws discussion (but it is now "following" from other axioms, and so Spinoza would not agree with someone claiming conservation laws do not follow from anything)... etc, etc.

grant hutchison
2009-Jul-29, 05:24 PM
If you don't like my tests or my conclusions, then you are free to accept Spinoza for your personal philosophy. That is the importance of the value and truths of philosophy not being abolute and not being testable in an objective laboratory.That's certainly the importance of your belief about the nature of value and truth. To you. :)

Grant Hutchison

DrRocket
2009-Jul-29, 05:28 PM
That's certainly the importance of your belief about the nature of value and truth. To you. :)

Grant Hutchison

You are continuing to change the meaning of what I say.

I made no statements with regard to value and truth outside the context of their discussion by philosophers.

DrRocket
2009-Jul-29, 05:51 PM
Well he's relevant if you are looking for relevance. For example, I find "From a given definite cause an effect necessarily follows; and, on the other hand, if no definite cause be granted, it is impossible that an effect can follow (http://frank.mtsu.edu/~rbombard/RB/Spinoza/ethica1.html#Axioms)" axiom very relevant to this thread - .

That "axiom" is completely irrelevant, for two reasons.

First, the issue at hand is whether or not causality is imposed by the laws of physics, particularly by general relativity. This axiom, if it were better formulated, would simply impose causality as an axiom, by fiat, thereby simply dodging the question.

Second the axiom gives no definition for either "cause" or "effect", and no relationship between the two other than temporal order. Thus is something happens and you find no "cause" you are simply barred from calling that something an "effect". If you follow this notion to a logical conclusion you find that there either there can be no big bang or that nothing that you see around you can be an "effect", as the chain from an effect backward to a cause can never end. Under Spinoza's axiom you cannot handle "initial conditions" and a free system evolving from initial conditions, but are rather forced to continually seek the "cause" of the initial conditions.

A discussoin of causality in the context of the usual mathematical models simply requires that having selected a time 0, that the response (time history of the state) of the system to an input that is 0 prior to time zero is identical to the unexcited system for times before 0 -- ie the system is non-anticipatory. Note this clearly identifies what is considered a "cause" -- the forcing function and the "effect" -- the difference in trajectory of the state in phase space between the excited and unexcited conditions given equal initial conditions.


Added it edit: Under Spinoza's axiom, radioactive decay cannot be an "effect" as there is no cause.

grant hutchison
2009-Jul-29, 06:08 PM
I made no statements with regard to value and truth outside the context of their discussion by philosophers.Well, no. You've made a quite particular connection between truth-testing and value (or "significance", earlier in the thread). It seems Feynman would probably have agreed with the way you link them, and I'm sure you'd also get agreement from many other folk as well, including some here at BAUT.

But since philosophers persist in finding value and significance in propositions which are not truth-testable in the way you've described, we're pretty much forced to the conclusion that they're either:
a) Dumb as stones, every last one of the them.
b) Not in agreement with your personal conception of value and truth.

The Feynman quote suggests that he went for option a). :lol:

(And with that, I suspect I've hijacked please's thread with this for much longer than is acceptable. Please respond as you will, and I'll undertake to make no counter-reply, no matter how much my fingers itch. :))

Grant Hutchison

please
2009-Jul-29, 06:46 PM
First, the issue at hand is whether or not causality is imposed by the laws of physics, particularly by general relativity.I think this is not (my) issue, since if you have specific theory (like GR) and formal definition of causality, then you should be able to find out unambigously if this theory entails causality or not, and this is exactly what Novikov et al were doing (and their conclusion was that causality holds only locally because wormholes are mathematically allowed). My issue could rather be interpreted as a question if it's possible to build successful theory equivalent to GR minus causality.


If you follow this notion to a logical conclusion you find that there either there can be no big bang or that nothing that you see around you can be an "effect", as the chain from an effect backward to a cause can never end. Under Spinoza's axiom you cannot handle "initial conditions" and a free system evolving from initial conditions, but are rather forced to continually seek the "cause" of the initial conditions.Couldn't we just assume that the cause is there? LCDM is doing exactly that, since its valid time range is limited by what we can see (so not even opaque Universe is in that range, not to mention Big Bang event itself).


A discussoin of causality in the context of the usual mathematical models simply requires that having selected a time 0, that the response (time history of the state) of the system to an input that is 0 prior to time zero is identical to the unexcited system for times before 0 -- ie the system is non-anticipatory. Note this clearly identifies what is considered a "cause" -- the forcing function and the "effect" -- the difference in trajectory of the state in phase space between the excited and unexcited conditions given equal initial conditions.Could you simplify this, I can't follow. Are you saying that causality means no change without input?



Under Spinoza's axiom, radioactive decay cannot be an "effect" as there is no cause.Again, we can just assume unknown cause, which is "there", somewhere.

Xtrozero
2009-Jul-29, 07:18 PM
No. You push one end of the stick. That force is propagated through the stick, molecule by molecule. One of the physics people here can explain in detail perhaps, but the point is, it's a process that takes time. It is not instant.

Yes, I agree, and Iím not suggesting that this operates under Newtonian physics, but my point is that it has been measured as faster than light speed when dealing with the connection of two photons.

Ken G
2009-Jul-29, 08:10 PM
Anyone is free to formulate their own philosophy any way they choose. No one should particularly care about anyone else's philosophy except perhaps as raw material for formulating their own.
I couldn't agree more, which is precisely the source of my objection to statements (say from you or Feynman) that philosophy has no significance, or is a waste of time or intellect. Obviously, by your own argument, if it has significance to some, then it does have significance. It just doesn't to you, and that's fine. The same could be said for music or art appreciation. Shall we take Feynman's words and substitute a Bach concerto everywhere he said a Spinoza proposition? Why would the result be something different, are there not people who personally find no value in Bach concertos?


I have never said that I hold philosophy in low esteem. I simply hold those who claim to be "philosophers" in low esteem. There is a difference. But you've never established any difference. Those who "claim" to be philosophers are not considered to be philosophers based on their own claim of such, that is simply not the process whereby influential philosophers are determined, any more than Bach "claimed" to be a composer.


Statements to the effect that Feynman "doesn't get it" or that his statements "lack insight" are also completely arbitrary. Not so, they are demonstrably valid statements (just as is the argument I present in this post), as long as Feynman's claim is to be interpreted as a critique of philosophy or philosophers, rather than a personal anecdote about his own relationship with that mode of human inquiry.

DrRocket
2009-Jul-30, 01:34 AM
I couldn't agree more, which is precisely the source of my objection to statements (say from you or Feynman) that philosophy has no significance, or is a waste of time or intellect. Obviously, by your own argument, if it has significance to some, then it does have significance. It just doesn't to you, and that's fine. The same could be said for music or art appreciation. Shall we take Feynman's words and substitute a Bach concerto everywhere he said a Spinoza proposition? Why would the result be something different, are there not people who personally find no value in Bach concertos?

No, you cannot take Feynman's words and substitute "Bach concerto" for "Spinoza proposition". That would be to misquote Feynman. He offered his opinion regarding Spinoza. He was silent on Bach.

I am quite sure that there are people who personally find no value in Bach concertos. If one of them uttered Feynman's words with "Bach concerto" in place of "Spinoza proposition" then it would be proper to make the substitution and also make the appropriate citation.


But you've never established any difference. Those who "claim" to be philosophers are not considered to be philosophers based on their own claim of such, that is simply not the process whereby influential philosophers are determined, any more than Bach "claimed" to be a composer.

Certainly I have. For instance I have quite clearly stated that I agree with Feynman's philosophy. I generally also agree with Will Rodgers, Harry Truman, and Mark Twain. Yogi Berra is not bad either. You can pretty well conclude that those that you consider "influential philosophers" fall into the camp of what I have labeled "professional philosophers".


Not so, they are demonstrably valid statements (just as is the argument I present in this post), as long as Feynman's claim is to be interpreted as a critique of philosophy or philosophers, rather than a personal anecdote about his own relationship with that mode of human inquiry.

Yes so.

Any critique (unless it is a rigorous logical proof and outside of mathematics critiques are generally not of such character), including your critique of Feynman's critique is a statement of an individual's opinion, perhaps bolstered by examples but nevertheless only an opinion. Since we are not dealing with "absolute truth" (whatever that is) it cannot be otherwise.

A critique must be taken in context. It is being articulated by an individual. That individual has no direct access to any supreme being who is the arbiter of "absolute truth". Anything critricism or endorsement from that individual is of necessity his opinion. That applies to my finding lack of value in the work of professional philosophers and your finding value in them. Moreover, it matters not a whit what the opnion of the majority might be. It is a purely personal and subjective decision.

DrRocket
2009-Jul-30, 01:48 AM
Couldn't we just assume that the cause is there? LCDM is doing exactly that, since its valid time range is limited by what we can see (so not even opaque Universe is in that range, not to mention Big Bang event itself).

If you do that you have altered Spinoza's axiom to read "There can be no effect without a cause, except when there isn't one."

LCDM is not doing what you claim. LCDM simply states that if you use a positive cosmological constant in GR then you get a prediction that seems to match observation. The issue as to the origin of the cosmological constant remains not only open, but a subject of vigorous research.

LCDM is not a complete theory. It is nothing more than a model that provides the impetus to do the research that one hopes will lead to a complete theory. Without some definition of "dark energy" or some other source for the cosmological constant it only a working hypothesis, and an incomplete one at that.


Could you simplify this, I can't follow. Are you saying that causality means no change without input?

Not quite. For instance if you have a body in motion it will continue to change position even with no input -- that is Newton's first law.

I realize that my formulation is a bit complex and abstract, but it seemed necessary in order to be precise and represent the intuitive notion of 'causality".

Intuitively a causal system is one that stays "at rest" until it receives a stimulus, that it is it does not anticipate the input and respond before it receives the input.


Again, we can just assume unknown cause, which is "there", somewhere.

No. That again is equivalent to "there can be no effect without a cause, unless there isn't one". An effect with a cause that is in principle not detectable is operationally equivalent to an effect without a cause. If you take the existence of the "cause" as a given then there is no content to the axiom. You could not, in principle, define a situation for which the axiom would be false -- because you have assumed the "cause" to always exist.

Ken G
2009-Jul-30, 02:07 AM
No, you cannot take Feynman's words and substitute "Bach concerto" for "Spinoza proposition". That would be to misquote Feynman. He offered his opinion regarding Spinoza. He was silent on Bach.I think you're missing the point. The substitution I indicate is not an identity transformation, rather, it is to expose the quality of Feynman's criticism. To address my complaint, you would have to give even a single reason why Feynman's opinion of Spinoza can be distinguished from some nonmusical boor's opinion of Bach. You have not done so, beyond saying that "it isn't testable." Neither is Bach, so the boor is still in an equivalent position as yourself.


I am quite sure that there are people who personally find no value in Bach concertos. Obviously. And their critique of Bach would be as insightful as Feynman's was of Spinoza. This is the point Grant and I are making, you can choose to reject it if that makes you more comfortable, but there it is.


Certainly I have. For instance I have quite clearly stated that I agree with Feynman's philosophy. That is completely nonresponsive to my objection. I objected to this statement by you:

I have never said that I hold philosophy in low esteem. I simply hold those who claim to be "philosophers" in low esteem. There is a difference.
As you can see, this statement has nothing at all to do with your own personal philosophy, which is irrelevant to the issue of the difference between philosophers and philosophies. You claim that the problem is people who "claim" to be philosophers, I tell you that their claims are as irrelevant as your mentioning said claims. They are philosophers because of the way their analyses are accepted by the educated philosophic community, and that is just a fact. I can easily make all your identical arguments about Bach ("I like music, my problem is with the people like Bach who claim to be composers"). That fact exposes the quality of the argument, even though Bach and Spinoza are indeed different people.


Any critique (unless it is a rigorous logical proof and outside of mathematics critiques are generally not of such character), including your critique of Feynman's critique is a statement of an individual's opinion, perhaps bolstered by examples but nevertheless only an opinion.Obviously. My critique of Feynman is not that he is registering an opinion, it is the quality of his argument. That is also what Grant objected to, quite specifically in his splendidly concise "rookie category error" characterization.

DrRocket
2009-Jul-30, 02:11 AM
But you've never established any difference. Those who "claim" to be philosophers are not considered to be philosophers based on their own claim of such, that is simply not the process whereby influential philosophers are determined, any more than Bach "claimed" to be a composer.


Is this an argument for the elimination of Departments of Philosophy ?

I think Bach claimed to be a composer. He composed music and I think sold his compositions. I think it is also recognized that the value of a musical composition is subjective. Some like Bach. I do. Some like rap. I don't. Rap has more contemporay influence than does Bach. Still, to me rap is crap. Others disagree. We can both be right. Music has no more claim to absolutes than does philosophy.

Influential philosophers seem to be annointed by people who are called Professors of Philosophy.

Now, if you consider those people who actually influence a significant number of people in modern society, then perhaps I would agree that there is some value in their thoughts. But when people talk of "influential philosophers" they usually do not have in mind John Wayne, Mark Twain, Yogi Berra, Will Rodgers, Norman Schwarzkopf, W.C. Fields, Richard Feynman, ....(people who make sense) :)

I have no idea if Spinoza claimed to be a philosopher. He certainly has that reputation now, compliments of Departments of Philosophy. As I recall he made a living as a lens grinder. I think lens grinding is an honorable and valuable profession.

But unless you can demonstrate to the contrary, I think I will stick with my assertion that Spinoza's axioms are of no help whatever in resolving the fundamental issue of the necessity or lack thereof of causality in physics.

Ken G
2009-Jul-30, 04:52 AM
Is this an argument for the elimination of Departments of Philosophy ?I'm going to assume that was intended as a joke, so requires no comment.

I think Bach claimed to be a composer. This precedes similar statements that are irrelevant to the discussion, so I'll skip commenting there also.

Influential philosophers seem to be annointed by people who are called Professors of Philosophy.
Yeah, and the people who prove math theorems call themselves "Professors of Mathematics." The nerve of these people. I still see zero relevance to anything said above.

But when people talk of "influential philosophers" they usually do not have in mind John Wayne, Mark Twain, Yogi Berra, Will Rodgers, Norman Schwarzkopf, W.C. Fields, Richard Feynman, ....(people who make sense) As opposed to "influential mathematicians" like Big Bird? Cuz the only people who think Riemann made more sense than Big Bird are, gasp, professors.
But unless you can demonstrate to the contrary, I think I will stick with my assertion that Spinoza's axioms are of no help whatever in resolving the fundamental issue of the necessity or lack thereof of causality in physics.What you fail to recognize is that causality is itself a philosophical notion, and the opinions of people like Hume on the topic are an excellent place to begin any consideration of it-- even in physics. Indeed, I have little doubt that googling "causality" and the "Stanford encyclopedia of philosophy" will reveal a wealth of extremely detailed thinking on the subject of causality, that we could spin our wheels on this thread for a year and still not happen on a single concept not contained in that google search.

DrRocket
2009-Jul-30, 06:16 AM
I have little doubt that googling "causality" and the "Stanford encyclopedia of philosophy" will reveal a wealth of extremely detailed thinking on the subject of causality, that we could spin our wheels on this thread for a year and still not happen on a single concept not contained in that google search.

How about this. Instead of just simply asserting that philosophy has a "wealth of extremely detailed thinking on the subject of causality", why don't you provide an example of a significant scientific conclusion regarding causality that can be obtained from or shown to originate in the work of some well-known philosopher.

If I have my druthers I would like to see a genuine scientific conclusion that you can draw from Spinoza's list of 42 axioms, but any example from any philosopher of your choosing will do nicely.

Surely if you find their work valuable, there is a illustrative example that you might produce to show that something that we might agree upon as having value originates with the work of one of these gentlemen.

DrRocket
2009-Jul-30, 06:42 AM
I'
As opposed to "influential mathematicians" like Big Bird? Cuz the only people who think Riemann made more sense than Big Bird are, gasp, professors.

Surely you don't believe this.

If you do I rather wonder what is being taught to physics undergraduates these days.

agingjb
2009-Jul-30, 07:07 AM
I suppose I would start with David Hume for a consideration of causality.

It does seem to me that criticisms of philosophy for not providing scientific conclusions are to some extent misplaced. I would have said that they were, now, separable disciplines.

please
2009-Jul-30, 09:36 AM
If you do that you have altered Spinoza's axiom to read "There can be no effect without a cause, except when there isn't one."... An effect with a cause that is in principle not detectable is operationally equivalent to an effect without a cause.So are you saying "operationally equivalent" is enough to say things do not exist? This is weak position, it's like blind person denying existance of light - all fine, until he gets sunburns.


You could not, in principle, define a situation for which the axiom would be false.And that is exactly why it is axiom. In some cases, you can replace them with their negative and still end up with valid conclusions (cough, Lobachevsky, cough), but that does not invalidate the idea of using a theory based on this axiom.

Len Moran
2009-Jul-30, 12:14 PM
I have never said that I hold philosophy in low esteem. I simply hold those who claim to be "philosophers" in low esteem.






Influential philosophers seem to be annointed by people who are called Professors of Philosophy.

Now, if you consider those people who actually influence a significant number of people in modern society, then perhaps I would agree that there is some value in their thoughts. But when people talk of "influential philosophers" they usually do not have in mind John Wayne, Mark Twain, Yogi Berra, Will Rodgers, Norman Schwarzkopf, W.C. Fields, Richard Feynman, ....(people who make sense) :)


I don’t know, I am unsure where you are leading us here. To remark that professional philosophers are annointed by philosophy professors seems self evident, exactly in the way that particle physicist’s (for example) are given credence by, well, particle physicists. You seem to give more credence to (say) a particle physicist rather than a professional philosopher because physics is testable and philosophy is not. I agree with all of that, but “testable” means to establish empirical reality, which I consider to be quite different from the absolute ground of things. The particle physicist however often seems to put forward a view of such testable notions as leading to an ontology that can be proclaimed to the public as “things that actually exist like little travelling balls”, (which might count in your eyes as being “influential” with regard to the public in the way that John Wayne was). Rarely have I heard a professional physicist explain in terms that the general public may appreciate, that physics may not actually lead to “truths” that are self contained independently existing from our input, - a notable exception is Bernard d’Espagnat (a professional physist), who rather than proclaims professional philosophers to be incompetent, actually studies them and offers a critique that seems to help him in what I consider to be a first rate analysis of the role of physics (from a perspective very much of a professional physist) in helping to establish what the “ground of things” may actually mean. I believe that Ken G, who is also a professional physicist, does the same on this board.

Yes physics achieves concrete things and philosophy doesn’t seem to. But I prefer to just glimpse under the concrete, and what I seemed to have found is a very murky world that is not at all appetising to realists, but seems to me to be a much more appropriate way in looking at the fundamental nature of reality that doesn’t seem to be any more testable and solid as that put forward by philosophers.

And yet I sense from your input on this board (which I always enjoy reading for the in depth knowledge you have) that you see physics as a means of modelling a reality that may never be accessible to us (but apologies if I miss represent you here). So I am confused as to what you are really saying in your consistent criticisms of philosophers. You say that you are not opposed to philosophy, rather you think the practitioners of philosophy have lost (or perhaps never had) the plot. So what role would you see your ideal philosopher as having within physics?, or do you think they should leave well alone? That’s a perfectly acceptable thing to say, as long as one accepts the default position inherent within it, namely that physics should be treated as engineering with no pretence of giving insight into the nature of a reality that exists outside of us as sentient beings. Very few physists however would find this a palatable view to take, but they would readily take on the banishment of philosophers.

Apologies for departing from the OP theme, but there does seem to be a couple of strands within it, so I don’t feel that I’m completely OT.

please
2009-Jul-30, 12:21 PM
OT does no longer matter in this thread :) it is now about philosophy.

Ken G
2009-Jul-30, 01:17 PM
How about this. Instead of just simply asserting that philosophy has a "wealth of extremely detailed thinking on the subject of causality", why don't you provide an example of a significant scientific conclusion regarding causality that can be obtained from or shown to originate in the work of some well-known philosopher.You really don't get it at all. Of course philosophy does not provide examples of scientific conclusions, I would have thought that obvious from the fact that philosophy is not science (the sole "criticism" of it that has been leveled anywhere in this thread). What it can do, and has done countless times in the history of science, is provide a basic language for picturing and defining scientific concepts (do you need any more examples than the "atom"?), which science then has the job of drawing its own conclusions about.

Surely if you find their work valuable, there is a illustrative example that you might produce to show that something that we might agree upon as having value originates with the work of one of these gentlemen.
Atom.
Cause.
Logic.
Empiricism.
How many more examples do you need of oriiginally purely philosphical concepts that were later adopted by science? How about science itself? (Note science cannot be used to define science.)

Surely you don't believe this. If you do I rather wonder what is being taught to physics undergraduates these days.
This question was in regard to whether or not I think the mathematics of Big Bird is more "influential" to most people than that of Riemann. Of course I believe that, it is obviously true. My pointing this out was in reponse to your similar claim that Yogi Berra's philosophy is more influential than Spinoza's-- by your definition of influential. My point is to expose the flaw in your definition of that word, not to say something about Big Bird and Riemann that anyone wouldn't already know.

Ken G
2009-Jul-30, 01:39 PM
But I prefer to just glimpse under the concrete, and what I seemed to have found is a very murky world that is not at all appetising to realists, but seems to me to be a much more appropriate way in looking at the fundamental nature of reality that doesn’t seem to be any more testable and solid as that put forward by philosophers. This is an important remark in regard to the OP issue of causality in science. An important thing to "get" about physics is that it really has a two-sided nature-- it can be viewed as a means for making predictions that can be verified after they've happened, creating a "track record" which one can then use to empower decision making (in highly specialized situations, often involving technology), or it can be viewed as a means to accessing truths about reality. Both these views of what physics could be share some cross section with philosophy, but the methods are quite different, and the questions that can be addressed also differ.

Nevertheless, it is important for any student of physics to recognize, part of what physics does is to generate a means for "telling stories", using a language that is fundamentally philosophical. We have found that the stories we tell in physics are generally not unique, and so do not have a claim on the "actual reality", which presumably is unique (a philosophical argument). The predictions that emerge from the stories test out well enough, for the observations of the day, but the stories vary wildly with the physicist and the timeframe. Thus, we must either divorce physics from its own stories, which leaves physics in a form that most people would view as rather radical (but this is what I try to do when possible, because I believe our language fundamentally limits us even as it empowers us-- another philosophical argument), or we can borrow from philosophy and imagine that our stories are conveying some sense of "understanding the truth", despite the fact that they are not unique and vary century by century.

This is all quite relevant to a thread on causality. The concept of causality has evolved scientifically since the original inception of the concept (by philosophers, of course-- given our modern definitions of scientists vs. philosophers). However, the scientists are still working on sharpening the scientiic teeth of this concept, and that is precisely what this thread is about. In most situations, the scientific concept of causality is very effective, but when taxed to the limit, cracks appear. It is a work in progress. Ergo, the same process continues that has always been going on: a fundamentally philosophical concept is being attempted to make fit into science. Nothing new there folks, the only issue is, do we need to blind ourselves to the role philosophy, and the "professional philosopher," plays in this process? This point is not the hijack here; it is the very need to justify it that is the hijack.

DrRocket
2009-Jul-30, 03:48 PM
So are you saying "operationally equivalent" is enough to say things do not exist? This is weak position, it's like blind person denying existance of light - all fine, until he gets sunburns.

The fact that a blind person cannot detect fire with his eyes in no way means that he cannot detect fire. Your analogy is faulty.

You are falling into the philosopher's ontological morass. The horse exists. It exists whether you are blind, deaf or dumb. It can transport you, it smells, and it makes your butt hurt if you ride it too long.

From the perspective of science, if someting is not detectable in principle then it may as well not exist. For theology and philosophy the situation may be different, but we are talking here about science.




And that is exactly why it is axiom. In some cases, you can replace them with their negative and still end up with valid conclusions (cough, Lobachevsky, cough), but that does not invalidate the idea of using a theory based on this axiom.

If you can replace a statement with its negative and still end up with a valid conclusion, within a single theory, then your theory is trival. For if both A and ~A are true then also A and ~A are false. And if you have a false axiom then, since a false premise implies anything, all assertions of your theory are simultaneously both true and false. In short, your system of axioms in this situation is utterly worthless.

There are cases in which one axiom may be independent of others. The parallel postulate of Euclid is one such example. So, yes, you can obtain valid mathematical theories that are represented by two separate theories based on distinct, axioms. However, the applicability of those theories to physics is a different kettle of fish entirely.

In fact if you look closely at the structure of mathematics, you will find that what were historically called the axioms of geometry are no longer treated as axioms. Both Euclidean and non-Euclidean geometries are now constructed using only the Zermelo-Frankel (plus choice) axioms that underly virtually of mathematics. The difference lies in definitions. For this we can than many mathematicians, but certainly Riemann is at the head of the line.

Abstract systems of axioms are of use in mathematics. There the usefulness depends on their logical consistency and that which can be derived from them. The situation as it now stands, however, is that all of the mathematics that is used in physics and virtually all of the mathematics that you will see anywhere is based on a single set of axioms -- Zermelo Frankel plus choice.

Physics has a pragmatic critieria for the usefulness of a mathematical theory. In physics the usefulness is a reflection of the utility in describing a physical theory which must have predictive power and which must be consistent with experiments performed in the real world.

So now, if you wish to demonstrate the power of Spinoza's axioms for science, please use them, and ordinary logic, to produce a useful scientific conclusion. Since we are talking about causality, a convincing argument with regard to causality would be nice. Simply quoting his axiom that we must have causality, however, will not do.

DrRocket
2009-Jul-30, 03:57 PM
This question was in regard to whether or not I think the mathematics of Big Bird is more "influential" to most people than that of Riemann.


As opposed to "influential mathematicians" like Big Bird? Cuz the only people who think Riemann made more sense than Big Bird are, gasp, professors.

No you did not say that Big Bird is more influential. You said that the only people who think Riemann made more sense than Big Bird are professors.

Your two statements are totally different and address totally different issues. If you change the question or the premise, then of course you can change the answer, but if you are speaking as a scientist you must do the former before you do the latter. Philosophers are apparently somewhat more flexible on the matter.

Ken G
2009-Jul-30, 04:11 PM
No you did not say that Big Bird is more influential. You said that the only people who think Riemann made more sense than Big Bird are professors.Correct, that's the reason Big Bird's mathematics are obviously more influential with most people than Riemann's. Is this hard for you to accept? It was your argument, you may recall. To 99.9% of the word, not a single word out of Riemann's mouth would sound like anything but pure gibberish (ergo the connection you missed between "thinking it makes sense" and "influential"). Given that, I find half-baked criticisms of philosophy on those exact same grounds to be curious.

DrRocket
2009-Jul-30, 04:12 PM
You really don't get it at all. Of course philosophy does not provide examples of scientific conclusions, I would have thought that obvious from the fact that philosophy is not science (the sole "criticism" of it that has been leveled anywhere in this thread). What it can do, and has done countless times in the history of science, is provide a basic language for picturing and defining scientific concepts (do you need any more examples than the "atom"?), which science then has the job of drawing its own conclusions about.

As this was in reponse to


How about this. Instead of just simply asserting that philosophy has a "wealth of extremely detailed thinking on the subject of causality", why don't you provide an example of a significant scientific conclusion regarding causality that can be obtained from or shown to originate in the work of some well-known philosopher.

I take it that you have no examples of conclusions that can be obtained from or shown to originate in the work of some well-known philosopher.

Ken G
2009-Jul-30, 04:15 PM
I take it that you have no examples of conclusions that can be obtained from or shown to originate in the work of some well-known philosopher.Hmm, I wonder what part of the detailed list of examples I gave you didn't notice?

Atom.
Cause.
Logic.
Empiricism.
and included the rules of science itself, such as what constitutes a valid test (something which obviously cannot itself be tested by science, so comes from, you guessed it, philosophy).

DrRocket
2009-Jul-30, 04:17 PM
Correct, that's the reason Big Bird's mathematics are obviously more influential with most people than Riemann's. Is this hard for you to accept? To 99.9% of the word, not a single word out of Riemann's mouth would sound like anything but pure gibberish (ergo the connection you missed between "thinking it makes sense" and "influential"). Given that, I find half-baked criticisms of philosophy on those exact same grounds to be curious.

So 0.1% of the world are professors ? And ONLY that 0.1% find Riemann more cogent than Big Bird ? Those are quantifiable assertions. Prove them.

You are also confusing "don't understand" with "understand, and have concluded that it is nonsense".

DrRocket
2009-Jul-30, 04:23 PM
Hmm, I wonder what part of the detailed list of examples I gave you didn't notice?
and included the rules of science itself, such as what constitutes a valid test (something which obviously cannot itself be tested by science, so comes from, you guessed it, philosophy).

[quote=Ken G;1540408]
Atom.
Cause.
Logic.
Empiricism.[/quuote]

If you are claiming to have addressed the question, please identify which of the elements in your list is a conclusion.

Ken G
2009-Jul-30, 04:24 PM
So 0.1% of the world are professors ? And ONLY that 0.1% find Riemann more cogent than Big Bird ? Those are quantifiable assertions. Prove them.
Again you miss the point, the 99.9% was giving Riemann the benefit of the doubt! The actual numbers are irrelevant to any but a pedant, so do not need to be quantified. Or do you dispute this claim:
The vast majority of people, when exposed to both the mathematics of Big Bird and Riemann, find the mathematics of Big Bird to be far more influential in their lives.
Hmm? It was your argument that only a small academic elite give philosophers their reputations. You just don't like seeing the full ramifications/inconsistencies of your own position.

You are also confusing "don't understand" with "understand, and have concluded that it is nonsense".No, it is you who confuse those words, because you think that you understand the philosphers and have concluded it is nonsense. I can expose that argument with a very simple syllogism:
1) assume you understand the philosophers
2) you conclude it is nonsense
3) the philosophers did not so conclude
4) assume the philosophers were not fools, and did understand themselves at least as well as you understand them
5) ergo, either you are much smarter than philosophers, or assumption 1 has led us to a contradiction.

I must confess that I also have been critical of various philosophers on various specific grounds. I have found fault in some of their positions. But I never question the basic viability of the questions they are asking, and I always accept the great difficulty in addressing those questions. Ergo, I never conclude that any famous philosopher was espousing "nonsense". I find insights in even the strangest contentions, like those of Zeno's paradoxes.

nokton
2009-Jul-30, 04:34 PM
I wold most certainly trust philosophers to ponder that point or any point. Ponder is what they do best, and ad infinitum. I would not expect a conclusion, however.

If you have evidence of any closed timelike loops consistent with general relativity than would be quite a discovery.

Current physics, however has problems with your closed timelike loop since it implies both
A---->B---->C and B---->C---->A hence both A---->B and B---->A (Edited to correct last ordering)
which is a serious problem.

Without causality the notion of predictability of events goes out the window, since you now have the potential to invert cause and effect. Not only invert them, but have the order be dependent on reference frame. If the order of events is not invariant, then I think you have rather a problem with ALL of physics.
Hi Rocket, not understand the Dr, but fits in with your post. Perhaps you could tell
us mortals what you have a doctorate in?
Read Alberts scenario on time and space, and in particular the theory of space-time
dragging around a supermassive black hole.
I find your post aggressive to a degree that mutes reasoned discourse.
One thing I have learned over many decades of study, is that certainty, in science,
or anything else, so many times proves to be an illusion.
Nokton

Ken G
2009-Jul-30, 04:35 PM
If you are claiming to have addressed the question, please identify which of the elements in your list is a conclusion.I already addressed that particular rookie category error long ago when I pointed out that it is not the purpose of philosophy to reach science's conclusions on its behalf, it is the purpose of philosophy, in its interactions with science, to provide a conceptual framework for science to base its primitive concepts on. That is what my list addressed, and that is just exactly what science has done, ever since philosophy gave birth to science. Philosophy also gave birth to mathematics, by the way, but that's another thread.

Len Moran
2009-Jul-30, 04:35 PM
From the perspective of science, if someting is not detectable in principle then it may as well not exist. For theology and philosophy the situation may be different, but we are talking here about science.


How, in principle would you detect a photon in flight? We have plenty of ways to observe and predict the relationship between a macroscopic "source" and a macroscopic sink (detector), but the bit in between, the picture of a travelling photon in vaccum seems to me to be a model to suit our inherent human concept of distance and time. I have nothing against the model, it serves its purpose very well in terms of empirical reality, but for me that's where it ends. So yes, to answer your question, for me, the "photon in flight" doesn't exist in terms of objective science because it cannot be detected, it only "exists" in a philosophical sense as a "picture" of something that may or may not exist, but is very likely to be outside of physics as I understand its methodology.

DrRocket
2009-Jul-30, 04:55 PM
You say that you are not opposed to philosophy, rather you think the practitioners of philosophy have lost (or perhaps never had) the plot. So what role would you see your ideal philosopher as having within physics?, or do you think they should leave well alone?

That is a good way of putting it. Thanks. I don't think I would say that they never had the plot.

In ancient times virtually all significant intellectual activity was labeled "philosophy". I think that then everyone was on the same page, and there were very few pages in the book.

With regard to science, I think the plot was lost when mathematics, physics, and science in general became distinct from philosophy. Roughly following Newton and Liebniz.

It seems to me that philosophy of science, as represented by those who do not themselves actually do science, is basically irrelevant. So, I chose the "leave well alone" option. Another option, which seems to be operating in practice, is for the professional philosophers of science to do their thing, while practicing scientists ignore them. That is operationally equivalent to "leave well alone", for science itself, but may be confusing to those on the outside looking in.


Thatís a perfectly acceptable thing to say, as long as one accepts the default position inherent within it, namely that physics should be treated as engineering with no pretence of giving insight into the nature of a reality that exists outside of us as sentient beings. Very few physists however would find this a palatable view to take, but they would readily take on the banishment of philosophers.


Physics is quite different from engineering. Its entire purpose is in fact to give insight. Physicists make the tools necessary to give insight. Engineers use that insight to build things. Sometimes they get along and sometimes they don't.

I also have no problem with figurative banishment of philosophers from physics. Physicists themselves seem quite competent at producing the philosophy necessary to accompany and illuminate physical principles without help from professional philosophers. Philosophers are effectively banished in any case, since they are almost (not universely as Ken G is a counterexample) ignored.

It seem to me that the position that you are presenting is that only philosophers are capable of addressing "the nature of a reality that exists outside of us as sentient beings." I think that everyone addresses those issues. I just think that modern professional philosophers are rather bad at it. Good physicists and mathematicians do not require a philosopher to tell them what it is that they are really doing. As far as I am concerned a professional philosopher has the same relationship to a scientists as a food critic with dead taste buds has to Julia Childs.

You may take Spinozas 42 axioms as symptomatic of the problem that I see. Axioms should be simple and "self evident". They should also lead to meaningful insight and conclusions. I find that Spinoza's axioms fail on all accounts. http://frank.mtsu.edu/~rbombard/RB/Spinoza/ethica5.html

With this I quit the discussion of philosophy, at least for this thread, with apologies to the OP.

Ken G
2009-Jul-30, 06:35 PM
Physics is quite different from engineering. Its entire purpose is in fact to give insight. Physicists make the tools necessary to give insight.I believe the point Len Moran is making, quite correctly, is that what you mean here by "give insight" is actually essentially pure philosophy. It is also what I've meant by the way philosophy affords us the language by which we can "tell stories" in physics, leading to said insights. In the absence of a philosophically supported language, physics is nothing but an algorithm for doing predictions (indeed, some have advocated the "shut up and calculate" approach to physics, but ironically none of the proponents of that school actually follow its tenets to their logical conclusion).

The basic issue is that physics takes on the task of establishing a certain mindset in the practitioner, the mindset of "I understand this", even though this is not required in principle for making effective predictions. The "I understand" component of physics is in fact philosophy. Now, in practice, it is required to have that mindset, or at least I know of no physicists who do not use that mindset. This establishes the close connection that physics will always have with philosophy, and the well-worn paths of the professional philosophers.

It is true that I have also argued for the benefits of physics breaking from its philosophic roots, but that is only because it needs to use different methodologies to continue on the path that philosophy started it on, not because the philosophy is "nonsense". I very much view physics as the prodigal son of philosophy, making its own way in the world, and like any teenager, disregarding the importance of its parentage. With this, I too will exit the topic of philosophy in regard to the issues of causality raised in the OP.

please
2009-Jul-30, 07:07 PM
The horse exists. It exists whether you are blind, deaf or dumb. It can transport you, it smells, and it makes your butt hurt if you ride it too long.

From the perspective of science, if someting is not detectable in principle then it may as well not exist.sorry, there's no difference beyond that you know how to detect horse, and you don't how to detect decay cause.


So now, if you wish to demonstrate the power of Spinoza's axioms for science, please use them, and ordinary logic, to produce a useful scientific conclusion. Since we are talking about causality, a convincing argument with regard to causality would be nice. Simply quoting his axiom that we must have causality, however, will not do.It will do for me, however, in the sense I explained above - if Spinoza could answer in this thread, he would agree that causality is pure dogma, and there should be the way around using it (though it is still unclear if this way could lead to "a useful scientific conclusion", as you put it).

grant hutchison
2009-Jul-30, 07:10 PM
1) assume you understand the philosophers
2) you conclude it is nonsense
3) the philosophers did not so conclude
4) assume the philosophers were not fools, and did understand themselves at least as well as you understand them
5) ergo, either you are much smarter than philosophers, or assumption 1 has led us to a contradiction.
But since philosophers persist in finding value and significance in propositions which are not truth-testable in the way you've described, we're pretty much forced to the conclusion that they're either:
a) Dumb as stones, every last one of the them.
b) Not in agreement with your personal conception of value and truth.:)

What I find interesting (and with please's permission am now able to bring up on this thread), is the level of antipathy I've encountered from physics/engineering folk, directed at philosophers and philosophy. One can barely mention philosophy here at BAUT, for instance, without someone dropping by to take a swipe. And Feynman is far from being the only physicist to (at least attempt to) sink a knife into a philosopher in print. A large number of smart people with university degrees seem to be quite prepared to believe that a large number of other smart people with university degrees are indulging in nothing but unreflective nonsense, and have been doing so for centuries. Those who hold this opinion sometimes (in my experience) manage to have arrived at it without taking a single philosophy course or opening a single philosophy textbook.
What is that about? Why such strong feelings?

I contrast this with my own colleagues, in medicine. I'm considered something of an odd-ball, certainly, for my interest in philosophy. (I'm also considered an odd-ball for my interest in physics.) But my colleagues will characterize their feelings about philosophy with phrases like "I'm just not interested" or "I couldn't get into it" or "I don't know what the point would be" or "it's too abstract". A couple have said they think it would be "over their heads", and one allows that he might take an interest in philosophy when he's "old".
These are very smart, hard-nosed, competitive folk, who insist on seeing evidence to direct and support their clinical practice, and who are far from being squeamish about pointing out when they think someone is talking nonsense. But they're content to let philosophy carry on and do its thing at the margins of their lives, while they simply offer that it's not to their personal taste or interest.

Maybe I'm just perceiving a difference where none actually exists, but I've fretted about it a little, and I don't think so. I'm left wondering what cultural, temperamental or intellectual factors might account for the difference.

Grant Hutchison

agingjb
2009-Jul-30, 07:22 PM
Like Grant Hutchison I'm puzzled by the antipathy to philosophy and philosophers on this site. As someone who has read some philosophy with interest, and who finds some value in that study, I suspect that I'm rather out of place here.

please
2009-Jul-30, 07:30 PM
Again you miss the point, the 99.9% was giving Riemann the benefit of the doubt! The actual numbers are irrelevant to any but a pedant, so do not need to be quantified.Professor percent in USA is 524,000 (http://en.wikipedia.org/wiki/Professors_in_the_United_States) * 100 / 307,026,000 (http://en.wikipedia.org/wiki/Usa) = 0.17% so Ken G was actually very close :D

timb
2009-Jul-30, 07:30 PM
Don't worry, we're not all philistines.

DrRocket
2009-Jul-30, 07:48 PM
sorry, there's no difference beyond that you know how to detect horse, and you don't how to detect decay cause.



I certainly know how to detect a horse, even if Aristotle had trouble with the issue.

I also know how to detect a cause. In fact that is rather what one means by an "effect" is it not ?

The issue of causal vs non-causal systems is somewhat more precisely defined. In that setting you have a system, you know what constitutes an effect, or an output, and you know what constitutes a cause, or an input. The question then becomes whether it is possible for a system to anticipate the receipt of an iinput and produce an output prior to the receipt of the input.

You can make this precise using mathematics in several ways. One is to ask if there exist closed time-like loops.

Another is to posit a system in a zero state, one in which the output is zero and in which it will remain zero in the absence of an input. Such systems are usually described with systems of differential equations. One then provides and input in the form of a signal that is zero for t<0 and asks whether it is possible for the output of the system to have non-zero content for t<0.

Is it possible to create, on paper, non-causal systems using mathematics? Yes. It is quite easy. Simply let the inputs be functions with compact support (zero outside of some interval) and let the output be the Fourier transform.
That is one easy way. Do these systems describe any known physical system ? No.

A "cause" that is in principle not detectable is, like anything that is not detectable in principle, irrelevant to science. There is a tremendous difference between not knowing HOW to detect a cause (your interpretation) and a cause being undetectable in principle (my stated condition). If you don't see the differeence then that is perhaps at the root of our iinability to communicate.

Ken G
2009-Jul-30, 08:18 PM
What is that about? Why such strong feelings?As this is a new wrinkle, I'll enter my thoughts on this-- I believe it is precisely the same impulse as that which makes a teenager deride the advice of the same parents who spent a significant chunk of their lives guiding and fostering said teenager. Teenagers don't usually say "my parents think I should do X, but I want to act independently and do Y. Perhaps as I get older I'll see the wisdom in X, but for now doing Y seems to be closer to my interests and current concerns." However, they might say that about the advice of a friend or maybe even a doctor or counselor. To me, that sounds like the stance of your medical colleagues.

So why then is the reaction more like "my parents are nuts, they want me to do X. Why can't they understand that Y is what is right for me? They are completely out of touch with my needs and concerns." I'm generalizing quite a bit, clearly, but I seem to detect that same intensity of rejection that Grant was talking about. Why do teenagers (and even older, often) seem to reserve that for their parents? I believe it is because there is a dynamic of trying to break for freedom, of feeling invincible and better, younger and stronger, not subject to the same foibles. There is a recognition that the origins of that person (or physics) stem from those parents (or philosophy), but there is now a breaking away that requires utter, almost ignominious, rejection of said origins. "I'm better than that, so the same fate won't befall me" is the rallying cry. I see vestiges of that in the attitude of physicists and mathematicians.

One sometimes sees the same attitudes among siblings, and among subfields like math and physics, or experimental and theoretical physics, etc. Here there is probably a tinge of competitiveness or defensiveness along with the break for independence. For example, I see experimentalists impugn theorists on the grounds that the theory is oversimplified or irrelevant, the experimenter only needs to know the outcome of the experiment itself. I see mathematicians trying to shame physicists for their lack of rigor, seemingly failing to notice that rigor does not play the same role in physics as in math, all the while some experimenters may be objecting to the attempts to impose rigorous mathematical structure (via idealizations and approximations) onto the experimental outcomes that that same theorist is already doing. And then of course there can be theorists (like Feynman) impugning mathematicians for taking their abstract games too seriously, or abstract mathematians (like Hardy) rejecting the use of mathematics to do anything demonstrably useful.

The bottom line is, due to competitiveness and striving for independence, there is considerable opportunities for animosities to emerge. Given that this is the default state of affairs, our efforts should instead be to work purposefully in the direction of mutual understanding and appreciation. Not because it is "politically correct" (another flash point for those given to animosity), but because such cooperation is simply more effective use of human intellect; you never know where your next useful insight will originate.

please
2009-Jul-30, 08:23 PM
A "cause" that is in principle not detectable is, like anything that is not detectable in principle, irrelevant to science. There is a tremendous difference between not knowing HOW to detect a cause (your interpretation) and a cause being undetectable in principle (my stated condition). If you don't see the differeence then that is perhaps at the root of our iinability to communicate.In case of radioactive decay, is the cause not detected in principle, or because you don't know how? What else, besides mathematical constructions that you choose to describe this effect, can give you grounds to suggest that decay, or tunneling, happens without any cause?

DrRocket
2009-Jul-30, 08:30 PM
In case of radioactive decay, is the cause not detected in principle, or because you don't know how? What else, besides mathematical constructions that you choose to describe this effect, can give you grounds to suggest that decay, or tunneling, happens without any cause?

Certainly. Tunneling and decay occur on a statistical basis. There is no way, even in principle, to predict when a particular neutron will decay, at least with our current level of understanding, which is quantum mechanics. The same applies to tunneling, some electrons tunnel and some don't, and you can't predict which ones will. In the case of tunneling you can affect the number that will tunnel based on the applied electric potential, so if you want to regard the statistics as the output then you might regard the potential as the cause. But I know of no "out" in the question of radioactive decay.

If you claim that there is a cause for decay, then please produce it, or provide a rigorous argument for existence based on premises that are generally accepted.

The logical onus is not on me to prove that there is a cause, but rather on he who states that all effects have a cause to produce that cause.

please
2009-Jul-30, 08:41 PM
There is no way, even in principle, to predict when a particular neutron will decay, at least with our current level of understanding, which is quantum mechanics. The same applies to tunneling...so, in other words, again, it's just that you do not know how to detect it? it is hard for me to interpret the above in any other way.


If you claim that there is a cause for decay, then please produce it, or provide a rigorous argument for existence based on premises that are generally accepted.Just two centuries ago people were dismissing atoms, because atomists could not present irrefutable evidence; neverless I am pretty sure atoms still existed at that time.


The logical onus is not on me to prove that there is a cause, but rather on he who states that all effects have a cause to produce that cause.Since when axioms have to be proved?

DrRocket
2009-Jul-30, 09:34 PM
Since when axioms have to be proved?

Since they purport to describe the physical world, they require evidence if not proof. Proof applies only to mathematics.


Added in edit. The most important features of a set of axoims is that 1) they not be contradicted by either themselves or by relevant experience and 2) they be sufficiently plausible to be readily accepted on intuitive basis as being "true" so as to be meaningful to a sizeable population. Not just any arbitrary list of statements is acceptable as a set of axioms.

please
2009-Jul-30, 09:45 PM
well there's plenty of evidence for that axiom, don't you think. which is why it even exists.

DrRocket
2009-Jul-30, 10:15 PM
well there's plenty of evidence for that axiom, don't you think. which is why it even exists.

No.

There is evidence for lack of closed time-like loops. There is a logical case for why one cannot travel to the past in the usual sense of science fiction. the axiom is no help in this regard.

There is clear evidence in radioactive decay that the axiom is violated, if you will accept that the decay products constitute an "effect".

In short that axiom lacks clear meaning and is useless for science.

You said it yourself, it is pure dogma.

please
2009-Jul-30, 10:53 PM
There is evidence for lack of closed time-like loops.I think your all-times favorite Feynman was behind single electron theory that, among other things, gave quite plausible explanation why we don't see closed time-like loops (note that in his theory they exist, but we simply do not see them).


You said it yourself, it is pure dogma.Yes, that's what (any) axiom is, it is to be accepted as granted. Just like you accept that there is no hidden cause to decay, and that particles just happen to pass through energy barriers randomly due to their nature. You then proceed to say that this assumption fits with observation (of the decay), just like that Spinoza's axiom matched what he could observe at the time of writing, there's really no difference.

please
2009-Jul-31, 10:04 AM
note that in his theory they existon the other hand, if there is just one electron they dont :( but it still works with many of them.

loglo
2009-Aug-01, 02:12 AM
Now I know why my physics tutor gave me that weird look when I said I wanted to do a philosophy unit.

nokton
2009-Aug-01, 06:05 PM
I have noticed in this thread (http://www.bautforum.com/against-mainstream/90895-faster-then-light-quantum-communication-possible-2.html) that people were dismissing physical possibility of faster-than-light information transmission on grounds that it would violate causality (roughly, cause must precede effects in all possible frames of reference). I have seen people discussing spinning wormholes in GR and how does that violate causality, and noone cared; here, howeveer, a guy tries to discuss entanglement, and his argument is dismissed because of causality

So I asked, among other things, is caulaity not a mere extrapolation of our limited human experience upon everything in the whole universe, and the response was "You can't die from being shot by a bullet - before that bullet was fired" (ironic, isn't it).

Leaving aside countless but little-relevant examples of how such an extrapolation of our experience failed in the past, why is causality so uber important? I mean doesnt all the math in physics just work both ways (although maybe differently) regardless of causality?
Please, you make a valid point, causality is but a side issue in the understanding
the universe, the point is, we have not yet the knowledge or intelligence to understand
what we discover, nor the wit to say, I do not know.
And that betrays our arrogance and limits our perception of the truth.
My point is, Please, faster than light travel or communication is, as yet,
beyond our comprehension, but possible.
Nokton.