[does space expand or are things just moving?]

[Shaula]

Ha Ha,thanks. Really brilliant and hilarious too. It accurately describes the absurdity that reigns in part of modern cosmology.

Actually think it better fits popular explanations of the effects that we observe. The observations and the maths are totally consistent - it is just that we get tied in knots trying to explain it or work out what is 'really' happening. Human logic is a poor tool to dissect things like this - things that are totally outside our experience. We grasp at straws, apply labels and then get confused when said labels lead us astray.

[Staticman]

Actually think it better fits popular explanations of the effects that we observe.

Totally disagree, this is not quantum mechanics, it is actually pretty straightforward, Ken G explained it clearly and what I quoted illustrated it.

[Cougar]

The universe described as "objects flying away" should have an observable center of expansion and an observable outer edge . From our Earthly point of view, the universe appears to be uniform and of equal distance in all directions with no observable edge so we appear to be at the exact center of expansion.

One would think so, sort of like one would think a heavier object falls more quickly than a lighter one. But if an 'explosion' model is constructed such that velocity is proportional to distance from the explosion, the mathematics works out so that observers far from the explosion (but not at the edge) would note that such a universe still conforms to Hubble's law.

But that's just devil's advocacy. I'm in the 'space actually expands' camp, although scientifically the observations are as yet insufficient and the theory is underdeveloped. Actually, "expands" is incorrect. It's more like it "reproduces". The additional space between widely separated objects is just like the space that was there before - it doesn't 'thin out.' This may be partially ATM, but it is consistent with Einstein's cosmological constant.

[Ken G]

Totally disagree, this is not quantum mechanics, it is actually pretty straightforward, Ken G explained it clearly and what I quoted illustrated it.

I think you may have misinterpreted what Shaula said-- it seems to me the two of you are actually agreeing. The "absurdity" of modern cosmology is not the application of GR to the cosmological principle in the presence of observational constraints and cluges like dark matter and dark energy, that's all pretty standard science and is generating a healthy stream of very testable hypotheses. Rather it is the effort to translate all that into layman's terms, at considerable cost to the structure of the actual theoretical models. Would you disagree with that?

[Shaula]

Rather it is the effort to translate all that into layman's terms, at considerable cost to the structure of the actual theoretical models. Would you disagree with that?

Yup, that was what I was trying to say. Modern Cosmology is not absurd - the models that make it up are internally logically consistent and, if expressed in the right language (maths) and without trying to use preconceived ideas of what 'should' happen, make sense. The absurd and paradoxical bits almost always stem from someone trying to 'explain' the models or translate them into what is on the surface a simpler explanation but on inspection turns out to have had these absurdities introduced into it by the way it is expressed. Taking the example of QM - a lot of electron dynamics makes no sense if expressed in terms of particles. Some makes no sense if expressed as waves. Because they are both concepts that we are trying to shoehorn the actual entities used by the logically consistent model into.

[Ken G]

One would think so, sort of like one would think a heavier object falls more quickly than a lighter one. But if an 'explosion' model is constructed such that velocity is proportional to distance from the explosion, the mathematics works out so that observers far from the explosion (but not at the edge) would note that such a universe still conforms to Hubble's law.

I don't think you are disagreeing with Bob Angstrom there, I think he is just saying that the explosion model always requires an edge, and that is just what we don't currently put into our cosmological models (preferring instead the aesthetic appeal of the cosmological principle extended arbitrarily beyond our observable horizon). I was just saying that I believe we can rule out explosion models purely locally-- we don't observe the necessary dynamics that one would have in an explosion, in particular a pressure variation on the same scale as the velocity variation. The "moving through space" global picture simply doesn't succeed in generating a self-consistent model.

But that's just devil's advocacy. I'm in the 'space actually expands' camp, although scientifically the observations are as yet insufficient and the theory is underdeveloped. Actually, "expands" is incorrect. It's more like it "reproduces". The additional space between widely separated objects is just like the space that was there before - it doesn't 'thin out.' This may be partially ATM, but it is consistent with Einstein's cosmological constant.

That's more like a guess looking forward to the next theory, rather than a ramification of the current ones. It would have to have something to do with why inflation selected a particular hyperslice of spacetime to expand like crazy, and perhaps was even the origin of the local Minkowski geometry-- I don't know if anyone knows which came first, Minkowski or inflation. Such guesses are a good way to motivate new theories, but have less than a stellar track record in the history of science!

[Strange]

But if an 'explosion' model is constructed such that velocity is proportional to distance from the explosion, the mathematics works out so that observers far from the explosion (but not at the edge) would note that such a universe still conforms to Hubble's law.

I had pretty much come to that conclusion trying to frame an answer to Jeff's earlier question. The key seems to be if "velocity is proportional to distance from the explosion" which wasn't immediately obvious (to me).

[Staticman]

I think you may have misinterpreted what Shaula said-- it seems to me the two of you are actually agreeing. The "absurdity" of modern cosmology is not the application of GR to the cosmological principle in the presence of observational constraints and cluges like dark matter and dark energy, that's all pretty standard science and is generating a healthy stream of very testable hypotheses. Rather it is the effort to translate all that into layman's terms, at considerable cost to the structure of the actual theoretical models. Would you disagree with that?

Yes, I would. Because if you examine it with critical attitude you easily realize that the perceived absudity might be a red flag that something is wrong about the "standard science" picture.
That doesn't mean that necesarily there is something wrong, but it's always healthy in scientific terms to keep an open mind, even if one is not allowed to elaborate the suspicions in this type of 'textbook science only' oriented forum

[slang]

Alice: "Thank you. I think."

Ain't language fun! Still, it helped us out of the trees. From arborous to ambiguous. Sometimes I just want to climb back.

[Hornblower]

Yes, I would. Because if you examine it with critical attitude you easily realize that the perceived absudity might be a red flag that something is wrong about the "standard science" picture.
That doesn't mean that necesarily there is something wrong, but it's always healthy in scientific terms to keep an open mind, even if one is not allowed to elaborate the suspicions in this type of 'textbook science only' oriented forum

If we examine it with a critical attitude and technically sound scientific methods, we can easily realize that the perceived absurdity is an artifact of the limitations of our senses, which are adapted to be adequate locally under the conditions in which we live. After all, it once was considered absurd by people of Aristotle's stature to consider the possibility that the Earth might not be at absolute rest.

The stuff of the cosmos is what it is and it does what it does, and does not care whether or not mortal humans such as ourselves think it is absurd.

[transreality]

With expansion of space, distance is increasing between objects. One object is not "flying away" from the other. That's an important point Ken G made.

I'm talking about the observations. So, can you determine that space is expanding without employing any observations of the velocities of objects in space?

[WayneFrancis]

I'm talking about the observations. So, can you determine that space is expanding without employing any observations of the velocities of objects in space?

There are no velocities when it comes to cosmological expansion. Velocity requires a direction and a rate. Cosmological expansion only has rates that can be agreed upon. The direction is unique for each observer.

[Ken G]

Yes, I would. Because if you examine it with critical attitude you easily realize that the perceived absudity might be a red flag that something is wrong about the "standard science" picture.

There's always "something wrong" about the standard science picture, that has been true positively 100% of the entire history of science. That's perfectly routine, it's no cause for concern-- it's just exactly how science works. If the process is generating a healthy stream of testable hypotheses, science is working fine. Good science is a process, not a destination. Modern cosmology is good science, it makes no difference if it is right or not. What scientific theory was ever right?

That doesn't mean that necesarily there is something wrong, but it's always hea[lthy in scientific terms to keep an open mind, even if one is not allowed to elaborate the suspicions in this type of 'textbook science only' oriented forum

I think there is a very important distinction to make here. There never was anything "ATM" about claiming that modern science is wrong. I'll claim that right now: modern science is wrong. Throw me into ATM, I said it! But wait, that isn't ATM-- all scientists know that modern science is wrong, it's a perfectly mainstream attitude. It's what gets scientists out of bed in the morning, in fact.

So what does "ATM" really mean? It means you think science is taking the wrong path to new hypotheses, not that it isn't "right." It is suggesting there is some other hypothesis that is more promising than, say, dark matter and dark energy. That would be ATM, because at the moment it is quite clear that all the progress is being made in the direction of dark matter and dark energy hypotheses. That doesn't mean other directions should not be given fair due, but it certainly means that other directions have to pass muster before we can justify major outlays of resources on them, when the resources directed toward dark matter and dark energy have been so dramatically fruitful so far.

[Ken G]

I'm talking about the observations. So, can you determine that space is expanding without employing any observations of the velocities of objects in space?

There is no such thing as an observation of a velocity of an object in cosmological space, the role of gravity is just too important and it makes the concept of relative velocity coordinate dependent, so not directly observable. The observable is always redshift, and GR knows how to handle that with language that does not involve velocity.

[Staticman]

There's always "something wrong" about the standard science picture, that has been true positively 100% of the entire history of science. That's perfectly routine, it's no cause for concern-- it's just exactly how science works. If the process is generating a healthy stream of testable hypotheses, science is working fine. Good science is a process, not a destination. Modern cosmology is good science, it makes no difference if it is right or not. What scientific theory was ever right?
I think there is a very important distinction to make here. There never was anything "ATM" about claiming that modern science is wrong. I'll claim that right now: modern science is wrong. Throw me into ATM, I said it! But wait, that isn't ATM-- all scientists know that modern science is wrong, it's a perfectly mainstream attitude. It's what gets scientists out of bed in the morning, in fact.

So what does "ATM" really mean? It means you think science is taking the wrong path to new hypotheses, not that it isn't "right." It is suggesting there is some other hypothesis that is more promising than, say, dark matter and dark energy. That would be ATM, because at the moment it is quite clear that all the progress is being made in the direction of dark matter and dark energy hypotheses. That doesn't mean other directions should not be given fair due, but it certainly means that other directions have to pass muster before we can justify major outlays of resources on them, when the resources directed toward dark matter and dark energy have been so dramatically fruitful so far.

You are saying exactly what I wrote. I said ATM is talking about the alternatives, not claiming that current science is not right in the trivial Popperian sense.

[Ken G]

You are saying exactly what I wrote. I said ATM is talking about the alternatives, not claiming that current science is not right in the trivial Popperian sense.

When you referred to "absurdities" in the current scheme, it sounded like you did not regard the modern approach as good science. Perhaps I read too much into the use of that word.

[Staticman]

There's always "something wrong" about the standard science picture, that has been true positively 100% of the entire history of science. That's perfectly routine, it's no cause for concern-- it's just exactly how science works. If the process is generating a healthy stream of testable hypotheses, science is working fine. Good science is a process, not a destination. Modern cosmology is good science, it makes no difference if it is right or not. What scientific theory was ever right?

You are playing with a distiction between "good" and "right" science that I don't share. Is modern cosmology good science? I certainly don't like generalizations so I'm not gonna answer that.
I would say that a certain attitude of dismissing without the benefit of the doubt any alternative that I observe in many modern cosmology apologists is not good science, but that's just my opinion.

[Shaula]

There is a world of difference between good science and right science. Good science is always good whereas 'right' science is only right until it is superseded by the new 'right' science.

I think your notion that modern cosmologists should take every single one of the hundreds of ideas they see out there and spend their time turning them from ideas into theories (or debunking them) as unfair. The normal dialogue you get into is something like this:
Alf: I am not a scientist but I have spotted a HUGE hole in the theory you espouse.
Bob: The one I have spent eight years getting my head around?
Alf: Yeah, I just read Wikipedia on it. And I have spotted a flaw you haven't.
Bob: Ummm...
Alf: Anyway I have an idea how to fix it. I think that spinning harmonic quintessence, when properly quantised, does the job.
Bob: That doesn't make sense
Alf: You have to use the words like I mean them, not how you hidebound scientific types use them.
Bob: OK explain
...some hours later...
Bob: But that contradicts GR!
Alf: GR is not right then.
Bob: And itself
Alf: You just don't understand....
Bob: And this evidence
Alf: Heck, every little detail! You expect me to have every little detail! You are the scientist YOU do it. I have had the idea, that is the hard part. Now go prove me wrong.

[Staticman]

I think you are biased by Forums, real science out there has nothing to do with your depiction.

[Ken G]

Yes, Shaula's depiction is more about the interaction between scientists and "flakes". Still, a different depiction with a similar theme is relevant for interactions between scientists:
Mainstream apologist: "Here is a hypothesis that agrees with current observations and guides future observations to test it, and it involves X dark energy and Y dark matter."
Alternative attacker: "But you don't know that is the correct model."
Mainstream apologist: "No one ever does. Did Newton? Let's hear what alternative hypotheses you have, and what observations they agree with."
Alternative attacker:"Umm... (long pause)... All the same, I feel my ideas are being suppressed. I should get more funding, so I can answer your question.
Mainstream apologist: "Answer the question first, then ask for more funding."

ETA: corrected repetition.

[Shaula]

I think you are biased by Forums, real science out there has nothing to do with your depiction.

I am a scientist. I stand by what I said.

I am not trying to start a big argument - just saying that I think the burden of proof should be with the claimant. And now I will shut up before a mod tells me to as this is in danger of hijacking the thread. Ummm, something about expansion?

[Ken G]

I would summarize the answer to the OP as being this: the OP presents a false dichotomy, by forcing us to choose between two possibilities that are both oversimplifications, and neither carries the crux of the meaning of our current best cosmological models. However, if forced to choose between them, at least "space itself expands" is a picture that projects the correct GR explanation onto one particular coordinate choice, whereas "objects are all moving away from each other" does not project the correct explanation onto any coordinate choice. The reason for that distinction is that the "objects are moving away from each other" language is so coordinate-dependent that it cannot be the explanation of observed invariants (like redshift), since coordinate choices can never alter the observations. In other words, there is a difference between looking at a correct explanation in language that is only true in one coordinate system (as for "space expands"), versus mistaking a coordinate system as a valid origin of the true explanation (as with "objects are moving away", or even the literal interpretation of "space itself expands"). What's more, there is the possibility that a future theory of space might actually allow us to assert that space itself does indeed expand (or reproduce, if you will), whereas it seems that there is no chance of a future theory that would allow us to say that objects are moving away from each other-- that seems to already contradict what we know.

[Staticman]

I would summarize the answer to the OP as being this: the OP presents a false dichotomy, by forcing us to choose between two possibilities that are both oversimplifications, and neither carries the crux of the meaning of our current best cosmological models. However, if forced to choose between them, at least "space itself expands" is a picture that projects the correct GR explanation onto one particular coordinate choice, whereas "objects are all moving away from each other" does not project the correct explanation onto any coordinate choice. The reason for that distinction is that the "objects are moving away from each other" language is so coordinate-dependent that it cannot be the explanation of observed invariants (like redshift), since coordinate choices can never alter the observations. In other words, there is a difference between looking at a correct explanation in language that is only true in one coordinate system (as for "space expands"), versus mistaking a coordinate system as a valid origin of the true explanation (as with "objects are moving away", or even the literal interpretation of "space itself expands"). What's more, there is the possibility that a future theory of space might actually allow us to assert that space itself does indeed expand (or reproduce, if you will), whereas it seems that there is no chance of a future theory that would allow us to say that objects are moving away from each other-- that seems to already contradict what we know.

That is a way to see it, but here are some views by a couple of cosmologists (Hogg, Chodorowski) that see it differently (rejecting the space expands view) while not even agreeing between them.
Now, this is but a tiny sample of what has been a harsh controversy among reknown cosmologists and relativists that has left no winner, simply put, no consensus has ben reached about the OP question even among mainstream cosmologists. It can be argued that these guys know what they are talkng about, know the math, have their phd.'s. I mean they are not using confused "popular explanations" as Shaula said, and yet they don't reach an agreement.

http://arxiv.org/abs/astro-ph/0610590
http://arxiv.org/abs/astro-ph/0601171
http://arxiv.org/abs/0808.1081
http://arxiv.org/abs/0911.3536

[Kyle Howdyshell]

I don't think we can accurately answer that question because in order for us to know if space is expanding wouldn't we have to know where the "end" or the boundary of space is. So, it would most likely be the objects just moving apart in many different "directions"; (if space had directions), due to many different forces acting upon the objects.

[Ken G]

That is a way to see it, but here are some views by a couple of cosmologists (Hogg, Chodorowski) that see it differently (rejecting the space expands view) while not even agreeing between them.

Actually, I think my view is quite consistent with both Chodorowski and Hogg. Chodorowski only rejects the language that "space is expanding" on grounds that physical quantities of importance should be observables (i.e., not coordinate systems) and that Occam's Razor should lead us to reject adding any unnecessary elements to our theory (which is consistent with the view that expanding space is only a projection of the correct answer onto a particular coordinate system, i.e.., it is less general than the full answer, it requires additional stipulations not necessary to the theory). In the second paper, Chodorowski makes the point that in a hypothetical gravity-free universe (not our own), we could find many of the same phenomena that are attributed to gravity in our universe, so it does not necessarily follow that these effects have to be due to spacetime curvature (a key element of what many people think of as expanding space).

Hogg is saying that one does not need space to expand because one can generate a perfectly suitable language by replacing the expansion of space with a mapping into continuously changing reference frames as we consider cosmological events seen by a chain of local observers, which is just another way of saying that comoving-frame coordinates don't have to be viewed as a global system, they can be viewed as a chain of local systems. None of that seems to contradict the prevailing answer that GR + cosmological principle + initial conditions provides the "explanation" of all our observations, including redshifts, and that breaking that answer down into more picturesque and physically suggestive language requires selecting a particular coordinate system and a particular pedagogical angle. None of that is anything but routine in physics-- we avert all problems by simply not taking the pictures we use to understand things too literally, mistaking them for "what is really going on."

Finally, I would point out that none of these different arguments for or against a certain language constitute disagreements about the cosmological model itself, they are pedagogical disagreements about the best ways to think about the cosmological model among experts, and also the best ways to communicate that model to the general public, which can be quite a different issue.

[Shaula]

I don't think we can accurately answer that question because in order for us to know if space is expanding wouldn't we have to know where the "end" or the boundary of space is. So, it would most likely be the objects just moving apart in many different "directions"; (if space had directions), due to many different forces acting upon the objects.

No, basically. Space is not thought to have an end. It can be viewed as expanding but not expanding into anything.

[Staticman]

Actually, I think my view is quite consistent with both Chodorowski and Hogg. Chodorowski only rejects the language that "space is expanding" on grounds that physical quantities of importance should be observables (i.e., not coordinate systems) and that Occam's Razor should lead us to reject adding any unnecessary elements to our theory (which is consistent with the view that expanding space is only a projection of the correct answer onto a particular coordinate system, i.e.., it is less general than the full answer, it requires additional stipulations not necessary to the theory). In the second paper, Chodorowski makes the point that in a hypothetical gravity-free universe (not our own), we could find many of the same phenomena that are attributed to gravity in our universe, so it does not necessarily follow that these effects have to be due to spacetime curvature (a key element of what many people think of as expanding space).

Hogg is saying that one does not need space to expand because one can generate a perfectly suitable language by replacing the expansion of space with a mapping into continuously changing reference frames as we consider cosmological events seen by a chain of local observers, which is just another way of saying that comoving-frame coordinates don't have to be viewed as a global system, they can be viewed as a chain of local systems. None of that seems to contradict the prevailing answer that GR + cosmological principle + initial conditions provides the "explanation" of all our observations, including redshifts, and that breaking that answer down into more picturesque and physically suggestive language requires selecting a particular coordinate system and a particular pedagogical angle. None of that is anything but routine in physics-- we avert all problems by simply not taking the pictures we use to understand things too literally, mistaking them for "what is really going on."

Finally, I would point out that none of these different arguments for or against a certain language constitute disagreements about the cosmological model itself, they are pedagogical disagreements about the best ways to think about the cosmological model among experts, and also the best ways to communicate that model to the general public, which can be quite a different issue.

wow, you surely know how to stretch interpretations until the original papers mean what you want them to mean, you could make a good politician. Perhaps you are right and people argue just for sport.

[speedfreek]

Staticman, if you missed it, Cougar posted a paper near the beginning of this thread that has some commentary on the "argument". It is definitely worth a read. I have been following this cosmological debate for a while now, and it seems to me to be exactly as Ken said, the argument is not about the theory itself. This is not so much a debate on how our observations match with different versions of a theory, it is more a debate about how we should best interpret a single theory. See what you think:

http://arxiv.org/abs/0707.0380

Expanding Space: the Root of all Evil?

[Spaceman Spiff]

That is a way to see it, but here are some views by a couple of cosmologists (Hogg, Chodorowski) that see it differently (rejecting the space expands view) while not even agreeing between them.
Now, this is but a tiny sample of what has been a harsh controversy among reknown cosmologists and relativists that has left no winner, simply put, no consensus has ben reached about the OP question even among mainstream cosmologists. It can be argued that these guys know what they are talkng about, know the math, have their phd.'s. I mean they are not using confused "popular explanations" as Shaula said, and yet they don't reach an agreement.

http://arxiv.org/abs/astro-ph/0610590
http://arxiv.org/abs/astro-ph/0601171
http://arxiv.org/abs/0808.1081
http://arxiv.org/abs/0911.3536

This paper -- Expanding Space: the Root of All Evil -- is definitely worth reading if you're interested in this question of "expanding space". These guys take Chodorwoski to task for being confused. And it sure looks like it to me.

The blog Cosmic Variance, run by cosmologist (not the biologist) Sean Carroll has a brief overview (Does Space Expand?) of the issue appearing in 3 papers, including Hogg's, the Root of all Evil paper, and another one by Peacock. Some of the experts chime into the comments section appearing below the blog entry, and the back and forth is enlightening.


Looks like speedfreek beat me to linking to The Root of All Evil paper.

[Staticman]

I knew those papers by Peacock and Lewis, and the blog though I hadn't seen that entry.
It all seems to come down to a problem with the analogies, that's true, I don't deny that, but this seems to be related ultimately with expansion itself seeming a bad picture of the underlying theory, and if expansion IS an interpretation of the theory, why do we base so much of modern cosmology in an interpretation that originates so much diatribe?