Time has a beginning?

[Zeuzzz]

Edited by Tricky: 

Edited to remove rule 12 violation.

Please do not personalize the discussion.

Replying to this modbox in thread will be off topic  Posted By: Tricky

 

[Perpetual Student]

They don't thin or cease - their distribution is uniform in some average sense. But the time scale is much, much, much, much longer than trillions of years.

Don't you find a cosmological theory a little peculiar that has time with a beginning but then time continuing on for eternity? It does seem a strange construction to me; I am curious as to why you do not find it so.
I understand your point that such a scenario is compatible with the laws of thermodynamics, whereas the cyclic alternative is not.
Can you not envision some way around that problem or perhaps something like this: the laws of thermodynamics operate within a brane in Steinhardt's model but do not operate in the "bulk" (as he calls it)?

 

[sol invictus]

Don't you find a cosmological theory a little peculiar that has time with a beginning but then time continuing on for eternity?

Yes, that particular combination of unlikely possibilities would be odd. But as I keep telling you, the concordance model of cosmology says precisely nothing about whether time began at the big bang, just as it says precisely nothing about whether or not the possibility I just outlined for the future is accurate. We simply don't know, because neither theory nor observation suffices to determine that.

Can you not envision some way around that problem or perhaps something like this: the laws of thermodynamics operate within a brane in Steinhardt's model but do not operate in the "bulk" (as he calls it)?

The laws of thermodynamics follow from statistics. All you need are more than one or two degrees of freedom. So it's very hard to see how they could be violated in a model for the entire universe.

 

[Perpetual Student]

Yes, that particular combination of unlikely possibilities would be odd. But as I keep telling you, the concordance model of cosmology says precisely nothing about whether time began at the big bang, just as it says precisely nothing about whether or not the possibility I just outlined for the future is accurate. We simply don't know, because neither theory nor observation suffices to determine that.

OK, but are there not some variations or versions of big bang cosmology that have time beginning or time emerging out of a space dimension? If time were to continue eternally, in one of those scenarios, we would have a strange unsymmetrical theory of time.

The laws of thermodynamics follow from statistics. All you need are more than one or two degrees of freedom. So it's very hard to see how they could be violated in a model for the entire universe.

Could it not be that a brane collision causes a massive decrease in entropy along with the creation of energy and matter in the cyclic model? This is merely a naive speculative question, not a claim.

 

[sol invictus]

OK, but are there not some variations or versions of big bang cosmology that have time beginning or time emerging out of a space dimension? If time were to continue eternally, in one of those scenarios, we would have a strange unsymmetrical theory of time.

Yes.

Could it not be that a brane collision causes a massive decrease in entropy along with the creation of energy and matter in the cyclic model? This is merely a naive speculative question, not a claim.

No. Collisions never decrease entropy - that's the whole point of it. Entropy is nothing more than probability - it increases because probable things happen much more often than improbable things. Collisions involve lots and lots of stuff, and the more stuff there is, the more absurdly unlikely it is that entropy will decrease.

 

[Perpetual Student]

No. Collisions never decrease entropy - that's the whole point of it. Entropy is nothing more than probability - it increases because probable things happen much more often than improbable things. Collisions involve lots and lots of stuff, and the more stuff there is, the more absurdly unlikely it is that entropy will decrease.

OK, I don't want to be misunderstood as debating this. It appears that there is no way to decrease entropy on a large scale because of the likelihood for things to become disordered (from a statistical perspective) -- do I understand that correctly?
Nevertheless, I am merely speculating about alternatives. Could there not be some phenomenon like an "anti-brane" colliding with a brane that could decrease entropy. It would be like adding energy to a system that is otherwise winding down, like, say, a roulette wheel being whacked by something -- !poor analogy!

 

[Jiddu]

Could it not be that a brane collision causes a massive decrease in entropy along with the creation of energy and matter in the cyclic model? This is merely a naive speculative question, not a claim.

Isaac Asimov -'The Last Question'..

2061, the world is cooling down, scientists ask of the Earth's super computer:
"Can entropy be reversed?" Computer says no, "Insufficient data for meaningful answer"

Next scene - Earths inhabitants have fled the white dwarf that used to be our sun for younger stars, and as the galaxy continues to cool they ask the super computer, the ark of all human knowledge, "Can entropy be reversed?"Insufficient data to give a meaningful reply".

This scenario continues through subsequent scenes during which the universe is becoming ever colder and dying out, as the computer becomes progressively more powerful. The answer however remains the same.

Trillions of years elapse, whereby almost all warmth and life in the universe has vanished. All knowledge is compacted in a wisp of matter in the near absolute zero of hyperspace. The wisp asks of itself "Can entropy be reversed" - "Let there be light" it responds. And there was light.

 

[theprestige]

OK, I don't want to be misunderstood as debating this. It appears that there is no way to decrease entropy on a large scale because of the likelihood for things to become disordered (from a statistical perspective) -- do I understand that correctly?
Nevertheless, I am merely speculating about alternatives. Could there not be some phenomenon like an "anti-brane" colliding with a brane that could decrease entropy. It would be like adding energy to a system that is otherwise winding down, like, say, a roulette wheel being whacked by something -- !poor analogy!

And how would you deal with entropy in this meta-brane full of brane and anti-brane collisions?

After all, the roulette wheel is ultimately a bound by the increasing entropy of the meta-system it inhabits.

Either it's going to be increasing entropy "all the way down", or you're going to have to arbitrarily introduce a mysterious decreasing-entropy metaverse somewhere along the line.

Which, mind you, doesn't strike me as any more or less strange as any of the other scenarios proposed (the big bang, the "beginnning" of time, etc.), except that we don't have any observations to support it, and we don't have any kind of a coherent, internally-consistent theory that both explains the observations we do have and predicts anything like it. So in that sense, time "beginning" at the big bang, and a subsequently inflationary universe, is demonstrably less bizarre than an entropy-decreasing anti-brane.

 

[Perpetual Student]

Isaac Asimov -'The Last Question'..

2061, the world is cooling down, scientists ask of the Earth's super computer:
"Can entropy be reversed?" Computer says no, "Insufficient data for meaningful answer"

Next scene - Earths inhabitants have fled the white dwarf that used to be our sun for younger stars, and as the galaxy continues to cool they ask the super computer, the ark of all human knowledge, "Can entropy be reversed?"Insufficient data to give a meaningful reply".

This scenario continues through subsequent scenes during which the universe is becoming ever colder and dying out, as the computer becomes progressively more powerful. The answer however remains the same.

Trillions of years elapse, whereby almost all warmth and life in the universe has vanished. All knowledge is compacted in a wisp of matter in the near absolute zero of hyperspace. The wisp asks of itself "Can entropy be reversed" - "Let there be light" it responds. And there was light.

That's great! I remember reading that many, many years ago.

 

[Perpetual Student]

And how would you deal with entropy in this meta-brane full of brane and anti-brane collisions?

After all, the roulette wheel is ultimately a bound by the increasing entropy of the meta-system it inhabits.

Either it's going to be increasing entropy "all the way down", or you're going to have to arbitrarily introduce a mysterious decreasing-entropy metaverse somewhere along the line.

Which, mind you, doesn't strike me as any more or less strange as any of the other scenarios proposed (the big bang, the "beginnning" of time, etc.), except that we don't have any observations to support it, and we don't have any kind of a coherent, internally-consistent theory that both explains the observations we do have and predicts anything like it. So in that sense, time "beginning" at the big bang, and a subsequently inflationary universe, is demonstrably less bizarre than an entropy-decreasing anti-brane.

I see your point.

 

[Perpetual Student]

This is S&T's answer to the entropy problem we have been discussing here.

"In the new cyclic model, the entropy created during one cycle is diluted during the period of accelerated expansion, but is not draw together (i.e., remains dilute) during the contraction period. The total entropy of the universe as a whole increases steadily from bounce to bounce, as demanded by the second law of thermodynamics. However, the entropy from the previous cycle is spread to regions beyond the horizon during the period of dark energy domination. So, as far as a local observer is concerned, the entropy density and the total entropy within the horizon is driven to zero each cycle and the universe appears to begin afresh..

The brane picture is the best way to explain how this occurs. The entropy consists of particles and radiation that lie on the brane. During the period of matter-, radiation- and dark energy-domination, the branes stretch and the entropy density is steadily reduced. After a trillion years of dark energy domination, so much expansion has occurred that the entropy density is nearly zero. During the contraction phase, the branes cease stretching, but they do not contract significantly, either. Instead, the extra dimension contracts to zero. Hence, the entropy density on the branes remains dilute all the way up to the bounce. At the bounce, new matter-radiation is created by the collision whose entropy density exponentially overwhelms any tiny remnant of older entropy density, making the latter irrelevant in the next period of cosmic evolution."

The above is from: LINK
There is also a similar description in the book Endless Universe. Any thoughts?

 

[sol invictus]

Any thoughts?

They try to escape this by claiming the universe is expanding as a whole, so even though the entropy in any given horizon volume is cycling between zero and some maximum, the total entropy increases. But this does not suffice.

First of all, the second law should be applied to the entropy in one horizon volume, not to the universe as a whole.

Secondly, even if that weren't the case the whole thing is still a perpetual motion machine, because it keeps cycling in a predictable way forever. That cannot and does not ever happen in real systems, because simple, coherent motions like that are never the most probable. They require many degrees of freedom to act together coherently, when uncorrelated random evolution of each degree of freedom is vastly more probable. As a result all real systems eventually come to an equilibrium, where everything is mixed, uniform, and at rest on average.

 

[Perpetual Student]

First of all, the second law should be applied to the entropy in one horizon volume, not to the universe as a whole.

Why?

 

[sol invictus]

Why?

Because that's the only formulation in which thermodynamics is compatible with gravity is cosmological spacetimes. See e.g. http://arxiv.org/abs/hep-th/9905177 .

But regardless, even if you don't buy that these cycles constitute a perpetual motion machine. All real systems tend to equilibrium (which in this case would probably mean uniform inflation).

 

[Perpetual Student]

Both the consensus model and the cyclic model have the appearance of being convoluted in that they both involve the piecing together of a number of theories and observations. Contributors here have provided adequate descriptions of this fact regarding the cyclic model. Steinhardt and Turok make the same observations about the consensus model in their book. Is there any disagreement about that?
So, it seems the central issue is entropy. Is that a fair assessment?

 

[sol invictus]

Both the consensus model and the cyclic model have the appearance of being convoluted in that they both involve the piecing together of a number of theories and observations.

No, I don't agree with that. The "consensus" model is built almost entirely from observations plus well-established theories (GR and the standard model of particle physics). The only speculative element is inflation, but that requires nothing beyond relatively standard particle physics (and the discovery of dark energy puts to rest much of the lingering doubt that such things actually work as expected). In return for some uncertainty in its cause, inflation buys you a very large number of predictions, many of which have been spectacularly confirmed over the last decade or so.

The cyclic model, on the other hand, requires wildly speculative assumptions about quantum gravity. Without any theoretical or experimental justification it simply posits that the singularity was resolved in just precisely the correct way to make the predictions match current data. Doing so in the way they assume requires the introduction of an exotic form of energy which violates known principles, and which almost certainly by itself leads to violations of the laws of thermodynamics (see the article I linked to earlier). Moreover the cycles themselves, if they are in fact eternal, violate those laws. And to top it all off, it hasn't made a single verified prediction.

To put it bluntly: as a scientific theory, it stinks.

So, it seems the central issue is entropy. Is that a fair assessment?

That's probably the central issue if you're most interested in whether time has a beginning. But for the cyclic model as a theory of physics, I think resolving the singularity is the central issue (they're related, but logically distinct).

 

[Perpetual Student]

No, I don't agree with that. The "consensus" model is built almost entirely from observations plus well-established theories (GR and the standard model of particle physics). The only speculative element is inflation, but that requires nothing beyond relatively standard particle physics (and the discovery of dark energy puts to rest much of the lingering doubt that such things actually work as expected). In return for some uncertainty in its cause, inflation buys you a very large number of predictions, many of which have been spectacularly confirmed over the last decade or so.

The degree to which your views diverge from those of Steinhardt and Turok is quite remarkable. It’s a chasm!

In their book, they describe the consensus model as resting on a number of unproven assumptions. Namely, “that big bang was the beginning of time,” … “the existence of … inflationary energy has to be assumed” … with … “specially tuned properties.” Then to explain cosmic acceleration, “dark energy, which has no connection to inflationary energy” is assumed. Then they say, “Cosmologists converged on the current version by stapling together different ideas” over the last century. Namely, ”the big bang model from the 1920s, dark matter from the 1930s, inflationary theory from the 1980s, and dark energy discovered in the 1990s. No overarching principle explains how or why any of these ideas requires the others.” … “Each piece has to be added independently and must be carefully adjusted to fit.”

Sorry for the deletions. I had to type this myself from the book. I believe I have not altered the meaning in any way.

I think I have made it very clear that I do not have the ability to analyze the cyclic model and come to any meaningful conclusions on my own, so my point here is not as an advocate of that theory. However I do find it quite disconcerting that such starkly opposing opinions about the consensus model exist. Steinhardt and Turok are not cranks; cosmologists who advocate the consensus model know their stuff; I have good reason to believe that your knowledge is quite genuine. It’s quite a dilemma for a layman.

 

[octogen80]

What we believe depends on the contents of our subconscious mind,which depends on what has been programmed into it.So you cannot express a unbiased opinion.Hence all the.biased replies we get.

 

[sol invictus]

The degree to which your views diverge from those of Steinhardt and Turok is quite remarkable. It’s a chasm!

Well, I'm afraid can't help you there. I really can't explain why they say what they say.

What I can do, though, is help you come to your own informed opinion. To do so, it's probably best to pick one or two specific statements or claims and focus on those.

In their book, they describe the consensus model as resting on a number of unproven assumptions. Namely, “that big bang was the beginning of time,”

That might be a good one to start with. Is it really true that the concordance model rests on that assumption? You're quite capable of understanding whether or not that's the case. If it's not true, that might be a hint as to the reliability of their arguments.

 

[Perpetual Student]

That (“big bang was the beginning of time,”) might be a good one to start with. Is it really true that the concordance model rests on that assumption? You're quite capable of understanding whether or not that's the case. If it's not true, that might be a hint as to the reliability of their arguments.

There are two problems here.
First, you are correct and I have no idea why the authors seem to repeatedly include that as part of the concordance model.
Second, towards the end of the book they seem to imply that inflation theory inevitably leads to multiverse theories (or pocket universes) and they seem to imply that inflation should occur again and again, creating a multitude of universes with differing properties. Now, this appears to be in total conflict with including "the beginning of time" with the concordance model, since such a process could be seen as having no beginning.

I was confused by the apparent contradictions in these two approaches. Perhaps one was Steinhardt and the other Turok?