(alpha) The Arrow of Time

I thought I'd start an alpha thread on this topic because there are two (presumably) different opinions on it in the blogosphere. I haven't read the blog entries yet, but I assume they're different because I know the people who are posting these things and I know they have opposing opinions.

The first entry is from Sean Carroll at Cosmicvariance.com.

The second is from Lubos Motl at his blog.

I shouldn't have to mention this, but this is an alpha thread. We will discuss this concept ``the arrow of time'' vis a vis the two opinions of Lubos and Sean. This is not a place for posting your own pet theories. As such, all off-topic posts will be deleted.

I just read the link by Sean Carrol, and I'm getting a lot of the directionality of time through. It's been recorded a lot longer though, that the arrow of time was something called the psychological arrow of time. http://en.wikipedia.org/wiki/Arrow_of_time

This does not mean however that consciousness is intimately designed as a cause and effect phenomenon. As far as consciousness can be concerned in relativity, no time passes at all, so it is a strange thing this phenomenon we call the arrow of time.
 
Sean Carroll's column is essentially the same argument as Brian Greene's in Fabric Of The Cosmos.

I found Motl's argument to be essentially, 'I don't agree with you, you should all agree with me'. It had the same air of certainty I've seen in many crank's posts.

Carroll and Greene's arguments seem clearer to me, and I found Motl's refutation of their point to be muddled.
 
Carroll mentioned Huw Price who wrote a book called "Time's Arrow and Archimede's Point", which I've read. The author's style, with quintuple negatives and half-page sentences, struck me as being complex to the point of "I'm just showing off to see how dizzy I can make you" (as one might expect from a professional philosopher), but the author's message is powerful and helped cement by suspicions about time symmetry.
 
I have to side with Carroll. I agree that entropy is a product of cosmology and the evolution of the universe. Each event has one preceding it, and the most likely outcome of these events is that the entropy of the universe will increase. I think that cosmology, as the history of the universe, has a lot to do with it.

blobrana's posts are pretty much what I have to say on the subject. I do think that entropy is hardwired into the universe - it is a matter of probability and pure geometry that the entropy of an unbound gas will increase over time. Couldn't geometry as we know exist without our universe?

I would also like to add that the arrow of time is something different than entropy. Entropy will sometimes decrease, but only due to the arrow of time. It may be possible to figure out what causes entropy, but the arrow of time is beyond mere mortals like ourselves.
 
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I have to side with Carroll. I agree that entropy is a product of cosmology and the evolution of the universe. Each event has one preceding it, and the most likely outcome of these events is that the entropy of the universe will increase. I think that cosmology, as the history of the universe, has a lot to do with it.

blobrana's posts are pretty much what I have to say on the subject. I do think that entropy is hardwired into the universe - it is a matter of probability and pure geometry that the entropy of an unbound gas will increase over time. Couldn't geometry as we know exist without our universe?

I would also like to add that the arrow of time is something different than entropy. Entropy will sometimes decrease, but only due to the arrow of time. It may be possible to figure out what causes entropy, but the arrow of time is beyond mere mortals like ourselves.

Entropy is one of those concepts isn't it, where the appearance of systems seem to get either more chaotic or more ordered. Entropy then is really a relative point of view.

Afterall, I would say the universe is a great deal more ordered now than what it was 15 billion years ago, despite the usual interpretation where systems have became more disordered. I don't believe Entropy is fully understood as anything more than a psychological view.

This is why things like the psychological arrow of time is intimately related entropy, and the way ''things apparently move''.
 
I never like answering binary question.

Choose between, "A or B, Wright or Wrong, Good or Evil?"

"Time, has no meaning to a photon." - Roger Penrose

Light in, Light out.
 
GD, entropy has a very specific meaning; it isn't relative or subjective. The entropy of a system can be measured, and this measurement would show that the universe is considerably less ordered than it was 15B years ago.
 
GD, entropy has a very specific meaning; it isn't relative or subjective. The entropy of a system can be measured, and this measurement would show that the universe is considerably less ordered than it was 15B years ago.

Oh yes, I agree completely. There is a certain agreement among physicists that entropy is indeed a measure of disorder.

But then I ask what is the disorder relative to?

For instance, we view the world with considerable order. In a process to understand this, we need to through our subjective means out the window and believe that a quark soup has more order, than let's say, the world we view today. I know that you will probably disagree, probably many will; but the universe to me is a very ordered place now. It seems a relative understanding as to whether one wishes to believe it is truely a measure of disorder, or rather, one of simply a change. What is disordered about today for instance? What is ordered about the past?

In fact, if we take some leading theories into consideration like top-bottom cosmology, order truely takes value here in the present, and is orderly shaping up our past too. How about that for a different opinion, or twist?
 
I know that you will probably disagree, probably many will; but the universe to me is a very ordered place now

Only on the small, local scale. You look at the universe and see ordered planets, stars and galaxies. Those are all small scale, local phenomena.
 
Only on the small, local scale. You look at the universe and see ordered planets, stars and galaxies. Those are all small scale, local phenomena.

Only 1% of all space and time is occupied by matter. The matter we see in the universe, is still very ordered, in their celestial arrays and planetary syncronization.
 
Green Destiny said:
But then I ask what is the disorder relative to?
It's relative to the measuring stick that we call entropy of the system. That is precisely how we compare the order of the present with the order of the past, and can say that the former is less than the latter. If you're using your eyeballs and saying "hey things look orderly to me" then you may be right but only in a local sense, as making that local order has come at the price of increased disorder for the larger system (i.e. we're all basically just processes responsible for churning the higher-energy photons of the sun into infra-red deep space emissions, and something like the Egyptian pyramids are a simple by-product of that).
 
It's relative to the measuring stick that we call entropy of the system. That is precisely how we compare the order of the present with the order of the past, and can say that the former is less than the latter. If you're using your eyeballs and saying "hey things look orderly to me" then you may be right but only in a local sense, as making that local order has come at the price of increased disorder for the larger system (i.e. we're all basically just processes responsible for churning the higher-energy photons of the sun into infra-red deep space emissions, and something like the Egyptian pyramids are a simple by-product of that).

Yes. I agree.

This would certainly be a local, yet subjective and relative sensitivity in the matter.
 
If we define "disordered" as being subjective, like "tasty", then I suppose you could say whatever you wish. However my point above was that if we define "disordered" as being equal to the measurement of entropy of a system (as we do), and we define entropy to have a specific and straight-forwardly measurable meaning (as it does), then the ambiguity is removed and we are able to specifically compare the disorderliness of two systems, or two points in time of a single system.
 
I think what I am saying, is that to say something is disordered, you necesserily require to take it as a subjective fact. If the big bang tastes like cake, then today we only have a mixture.
 
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