Three arrows of time.

[Menikmati]

The three arrows of time are the thermodynamic arrow, phychological arrow, and the cosmological arrow. The thermodynamic arrow is where disorder increases with time, the psychological arrow is why we remember the past but not the future, and there is the cosmological arrow is which the universe expands rather then contracts. It is said that the thermodynamic and the psychological arrow of time are connected together in which they both run on the same path. So does the cosmological arrow just run on its own path all by itself or does it have any relation with the thermodynamic and psychological arrow of time? The reason asking is because if you believe in the big crunch then the cosmological arrow must reverse itself for the universe isn't expanding anymore and if the cosmological arrow is related with any of those two then those two must also reverse. Then in the big crunch the dish that you just broke would simpy be back to its fixed state and you would know remeber the future instead of the past. I mean its really not likely for that not to happen but what do you think or know about this subject? Thanks

[Matthew]

The thermodynamic arrow is where disorder increases with time, the psychological arrow is why we remember the past but not the future, and there is the cosmological arrow is which the universe expands rather then contracts

Who says the universe will not contract? We do not know this for a fact.

[Menikmati]

Ahh yes that is true , but that it theory is if you believe in the big crunch.

[DippyHippy]

Why does disorder increase with time? Surely "in the beginning" there was chaos in the universe and now there's (relatively speaking) order`?

[Matthew]

Its entropy. There was chaos, but all the matter was clumped, over time though it spread out, entropy. Entropy is decreased by gravity, even cancelled out. If there is enough gravity entropy is reversed and we'll have a big crunch.

[DippyHippy]

I'm not sure what you mean by entropy... could you explain a little more please?

[Haglund]

My questions:
Is it possible to imagine a creature that remembers the future?
If there are three arrows of time, are there then three futures?

[Matthew]

Is it possible to imagine a creature that remembers the future?

I don't think so. How can something remember what hasn't happened yet?

[Haglund]

Originally posted by matthew@Nov 7 2003, 11:38 PM

Is it possible to imagine a creature that remembers the future?

I don't think so. How can something remember what hasn't happened yet?

I was thinking about this just now, I've read that if tachyons do exist, they would go back in time? What does that even mean? That their age is decreasing? If so, then how old were they?

And here is something interesting to read:
http://spot.colorado.edu/~vstenger/Briefs/...TimeTravel.html

[cosmocrazy]

I don't think so. How can something remember what hasn't happened yet?

Myself and another baut member mentioned something similar to this in an OTB post earlier this wk. Where we both had had dreams about the future that came true. We somehow "remembered" the future. I realise this is not mainstream but I thought I'd just mention it for something to think about.

Just going back to the OP. Since time is relative I would think that our perception of time is just the way we are wired. What we consider entropy and chaos maybe real order for the universe. A massless particle experiences no time based on GR. Its a big question which we can only answer based on our own perception.

[astromark]

Firstly Menikmati. No.Even if the accelerating expansion were to stop and begin to implode the Universe. Time would roll on regardless until the massive gravity well slowed time itself... This is as you said not a realistic view of our Universe.
So we have darted across the universes and find just the one arrow of time. Relentlessly rolling forward. To have a hypothetical reversal... No. Not now then or ever...
yes I did say never... Time is not a thing you can move through. The universe does not remember yesterday.
Humanity does have a ability to remember as fact what never was... Do not look in some tabloid paper for scientific facts. Look to the scientific community for your answers...

[DrRocket]

The three arrows of time are the thermodynamic arrow, phychological arrow, and the cosmological arrow. The thermodynamic arrow is where disorder increases with time, the psychological arrow is why we remember the past but not the future, and there is the cosmological arrow is which the universe expands rather then contracts. It is said that the thermodynamic and the psychological arrow of time are connected together in which they both run on the same path. So does the cosmological arrow just run on its own path all by itself or does it have any relation with the thermodynamic and psychological arrow of time? The reason asking is because if you believe in the big crunch then the cosmological arrow must reverse itself for the universe isn't expanding anymore and if the cosmological arrow is related with any of those two then those two must also reverse. Then in the big crunch the dish that you just broke would simpy be back to its fixed state and you would know remeber the future instead of the past. I mean its really not likely for that not to happen but what do you think or know about this subject? Thanks

You have recognized three "arrows". Whether or not they are arrows of time is quite another question.

The fact of the matter is that we do not have a sufficiently deep understanding of time to answer your questions definitively. The laws of physics, as they are presently understood, are symmetric with respect to time. We definitely perceive time as progressing from the "past" to the "future" but there is no fundamental understanding of why this is.

It is clear that, in our experience, time flows in only one direction, but we have experience with only a short span of time in comparison to the cosmological span reflected by your question. There is no reason to expect things to be different in that framework, but neither is there a fundamental explanation as to why that should be. Such an explanation would require a theory in which time was not taken as a fundamental entity, but rather was a quantity that resulted from some or several more fundamental notions, perhaps a statistical concept (Einstein, among others, is said to have thought that time would ultimately be found to be statistical in nature). But no such theory currently exists.

The best available theory of time and space is general relativity. But it is not sufficiently fundamental in its treatment of time to address your questions. And with respect to local physics, such as the physics of elementary particles which involve quantum phenomena, we have no theory that is able to treat both general relativity and quantum phenomena. So again your questions go unanswered and unanswerable within our present knowledge.

So the bottom line, despite statements made lo the contrary in this thread, is that nobody knows. Perhaps some future theory will be able to answer your question. But only time will tell. And in the meantime, time marches on.

[hhEb09'1]

Why does disorder increase with time? Surely "in the beginning" there was chaos in the universe and now there's (relatively speaking) order`?

If everything were "clumped" in a single "small" "region" then that might be the ultimate in "order", no?

If you look at any attribute that we use to differentiate things today, a histogram of that attribute would probably show a high peak early in the age of the universe--high order, in other words. Entropy has increased since then.

[Ken G]

So does the cosmological arrow just run on its own path all by itself or does it have any relation with the thermodynamic and psychological arrow of time?

That's a very tough question. It is expected that even in a big crunch scenario, time will advance the same way it does now (broken dishes won't come together), it will just happen against a backdrop of a contracting rather than expanding universe. In that sense, there really is no cosmological arrow at all-- the direction of cosmological time is arbitrary, and is by convention chosen to be the same as the thermodynamic and psychological arrows. The equations of cosmology (GR, basically) don't care what direction time is going, they're happy to be interpreted as time or minus time, where time is the thermodynamic version.

Your questions touch on an extremely important, subtle, and widely misunderstood element of physics: how much of it is done by us. Physics is not a set of laws that the universe is obeying, it is a set of laws invented by us to try and understand how the universe is behaving. Time is a perfect example of this general principle. We have found time to be a useful concept because of the way our minds work, we are looking through the "mirror darkly" whenever we use our minds to think about the universe. Our minds are part of the universe, so it's not surprising that some aspects of the universe are imprinted on our minds, and our minds have evolved to be successful in thinking about the universe, so it's not surprising that we do achieve considerable success, but the degree of success is mind-boggling, and that pun is intended.

In short, we choose to order events in terms of a time sequence, because we find that is a useful parameter for continuously predicting outcomes, and it also dovetails with the useful concept of cause and effect. Further, it gibes with our perceptions of experience and memory. So we like time, it works for us. But you can ask yourself, what would the universe be like if time routinely went backward and forward at will, constantly obeying the laws of physics as we know them? It appears from our most fundamental laws (which are purely deterministic and time reversible) that there is no way we could ever perceive or measure or falsify such a behavior of time. So it seems that the thermodynamic arrow, and the psychological arrow, both represent choices we make about how to order things, rather than a "truth" about how things are "really ordered".

Put differently, who says the future hasn't happened yet? We do, it's our language, our choices, stemming from our way of processing and perceiving. It works for us, we can't say much more. But when you read a historical story about some ancient figure, and what they were perceiving was their past and their probable future, from our standpoint their future has happened, and from theirs, it has not. Which one is right?

[slang]

6 year old posts, folks.. a 2012-related post was added to this thread but moved later.

[astromark]

Aaagh... ! must look at the date from time to time... Oops and thanks 'slang'