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Time has a beginning?

Perpetual Student said:
So, explain why the creation of the universe out of nothing does not violate the laws of thermodynamics.
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First, that has nothing much to do with inflation. For the third time, one reason inflation succeeds is that its predictions are independent of the physics of the singularity (or whatever replaces it).

Second, in the standard concordance cosmological model all the laws of thermodynamics are satisfied all the way down to any instant after the singularity. Precisely what happens at the singularity is unknown, but there is absolutely no evidence or theoretical reason to posit something there which violates any laws (on the contrary).

Third, there exist many speculative models which remove that singularity and are consistent with the laws of thermodynamics. The (eternal) cyclic model is not among them, but the Hartle-Hawking instanton I mentioned before probably is - in fact, it's motivated in many ways by thermodynamical reasoning.
 
sol invictus said:
That's why people often add coins to the analogy: you should imagine some coins glued to the surface of the balloon. As the rubber stretches the coins remain the same size, just as galaxies do (apart from their own evolution).
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That's helpful. (Though again, I think the coins represent galaxy clusters and not necessarily individual galaxies.)

I just read a Martin Gardner book where he keeps using the analogy of raisin bread (or muffins or whatever such that the dough expands when they're baked). If you considered any two raisins (galaxy clusters), the farther apart they are to begin with, the more quickly they are retreating from each other.



I think you're in violent agreement. arthwollipot's point was that the expansion of the space is too slow to counterbalance the attraction. (That's not a very precise way to think of things, but it works at least roughly.)
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Yes, we're saying the same thing, but differing on how best to explain it. I don't think it's useful to say that the universe is expanding between the Milky Way and Andromeda but that gravity is counterbalancing that expansion--at least no more than it is useful to say that the universe is expanding between the molecules in my body but that gravity and other attractive forces is compensating for that expansion.
 
JoeTheJuggler said:
That's helpful. (Though again, I think the coins represent galaxy clusters and not necessarily individual galaxies.)
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Well, it's certainly possible there are some isolated galaxies. But in general, yes, you're right - the largest gravitationally bound structures are galaxy clusters, which contain hundreds of individual galaxies.

I just read a Martin Gardner book where he keeps using the analogy of raisin bread (or muffins or whatever such that the dough expands when they're baked). If you considered any two raisins (galaxy clusters), the farther apart they are to begin with, the more quickly they are retreating from each other.
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That works too, and has the advantage of being 3D.

Yes, we're saying the same thing, but differing on how best to explain it. I don't think it's useful to say that the universe is expanding between the Milky Way and Andromeda but that gravity is counterbalancing that expansion--at least no more than it is useful to say that the universe is expanding between the molecules in my body but that gravity and other attractive forces is compensating for that expansion.
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In some technical sense you're right - gravity does not satisfy the superposition principle (i.e. its behavior is not just the sum of a bunch of forces). But it's still true that the reason the galaxy or galaxy cluster doesn't expand is that its self-gravitational attraction is stronger than the force of the overall expansion. And in fact if you imagine increasing the total mass of the universe - making galaxy clusters a little denser, for example - the whole thing becomes gravitationally bound. That means the space (on average) expands for a while, but then reaches a maximum, begins to contract, and eventually crunches into a singularity.
 
Perpetual Student said:
Really?

"Your question is absurd."

"... you don't understand what you're discussing."

Do those comments belong in a "healthy dialog"?
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Yes - they express sol invictus's opinion of your question and your understanding. So they belong in my definition of a "healthy dialog" where comments above are intended to evoke a response, e.g. did you clarify why your question was not absurd or that you understood what you were discussing?

ETA: A little context is useful.
sol invictus said:
Your question is absurd. First of all, your premise (the way you describe inflation) is wrong on just about every level. Secondly, one cannot evaluate those two possibilities on the basis of which one makes more sense to us, because our ideas about what is sensible are based on experiences with almost no relevance to this question.

But if you want a "common sense" reason why a cyclic universe is impossible, here's one: it's a perpetual motion machine.
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sol invictus said:
First, that has nothing much to do with inflation. For the third time, one reason inflation succeeds is that its predictions are independent of the physics of the singularity (or whatever replaces it).
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As I already said, the authors use the expression "the inflationary model" for a description of the history of the universe that includes (1) a big bang, (2) an inflationary period, (3) a period of dominant radiation, (4) a period of dominant matter, followed by (5) a period of dark energy dominance. I am sorry if the authors have led me to use a non-standard expression for all of that. I thought I already explained that. What should I call it? -- The "standard concordance model of cosmological history"? OK, then.


Second, in the standard concordance cosmological model all the laws of thermodynamics are satisfied all the way down to any instant after the singularity. Precisely what happens at the singularity is unknown, but there is absolutely no evidence or theoretical reason to posit something there which violates any laws (on the contrary).
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I was asking why, at that instant when a singularity appears out of "nowhere," "nothing" and "timelessness" the laws of thermodynamics are not violated? I don't believe anyone has explained that -- if there is an explanation.

Third, there exist many speculative models which remove that singularity and are consistent with the laws of thermodynamics. The (eternal) cyclic model is not among them, but the Hartle-Hawking instanton I mentioned before probably is - in fact, it's motivated in many ways by thermodynamical reasoning.
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OK, that's what I was asking about. Since I have no idea what the Hartle-Hawking instanton is, I'll have to look into it. The authors have an explanation involving the endless cosmic oscillation of branes coming in and out of contact that they claim solves the thermodynamics question. I have not read that part yet -- so, stay tuned.

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Look, I am a layman, searching for answers. I can't even come close to exploring these questions from the point of view of a physicist. I am struggling to understand this stuff. There is no need for acrimony. I have mentioned my prejudice against a theory that everything, including time, instantly came out of timeless nothingness -- whatever that means. But I have no genuine way of knowing if the "standard concordance model of cosmology" is correct or not.
 
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Perpetual Student said:
I was asking why, at that instant when a singularity appears out of "nowhere," "nothing" and "timelessness" the laws of thermodynamics are not violated? I don't believe anyone has explained that -- if there is an explanation.
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I thought that the explanation was: If a "singularity" (the universe presumably) appears out of "nowhere," "nothing" and "timelessness" then the laws of thermodynamics are not violated because they did not exist. You cannot violate a law when it did not exist.
In a sense this scenario includes the creation of all of the laws of physics at the same time as the creation of the universe since they (IMHO) depend on there being "somewhere", "something" and/or "time".
 
Perpetual Student said:
Look, I am a layman, searching for answers. I can't even come close to exploring these questions from the point of view of a physicist. I am struggling to understand this stuff. There is no need for acrimony. I have mentioned my prejudice against a theory that everything, including time, instantly came out of timeless nothingness -- whatever that means. But I have no genuine way of knowing if the "standard concordance model of cosmology" is correct or not.
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The concordance model of cosmology is correct as far as it explains most of the things that we observe about the universe. The only major outstanding issue is the abundance of lithium in the universe (the model is out by a factor of 2).
The concordance model does not include the beginning of the universe or what came before it.
 
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Reality Check said:
The concordance model of cosmology is correct as far as it explains most of the things that we observe about the universe. The only major outstanding issue is the abundance of lithium in the universe (the model is out by a factor of 2).
The concordance model does not include the beginning of the universe or what came before it.
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From Steinhardt and Turok:

"In the inflationary picture, the big bang was the moment of creation....The universe is assumed to come out of nothing, ..."

So, this is the basis of my terminology here. I have been using the terminology used by the authors, not knowing it was not universally understood as they have used it. Later, they say:

"Unlike the inflationary picture, the cyclic model does not include a moment when the temperature and density become infinite."


Reality Check said:
I thought that the explanation was: If a "singularity" (the universe presumably) appears out of "nowhere," "nothing" and "timelessness" then the laws of thermodynamics are not violated because they did not exist. You cannot violate a law when it did not exist.
In a sense this scenario includes the creation of all of the laws of physics at the same time as the creation of the universe since they (IMHO) depend on there being "somewhere", "something" and/or "time".
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That seems to be a bit of specious reasoning to me. It appears that either the laws of thermodynamics will be repeatedly violated under the cyclic model or violated all at once under the "singularity" senario.
 
Perpetual Student said:
From Steinhardt and Turok:

"In the inflationary picture, the big bang was the moment of creation....The universe is assumed to come out of nothing, ..."

So, this is the basis of my terminology here. I have been using the terminology used by the authors, not knowing it was not universally understood as they have used it. Later, they say:

"Unlike the inflationary picture, the cyclic model does not include a moment when the temperature and density become infinite."
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As stated before - Steinhardt and Turok have probably dumbed down their terminology for their audience. The concordance model specifically excludes t=0 because there is a mathematical singularity there. This does not mean that there is infinite pressure or temperature there. It means that these quantities are undefined. That is a major reason that GR is considered incomplete until quantum effects are included. The hope is that this will remove the mathematical singularity and allow pressure and temperature to have defined valued at t=0.

The alternatives are that they do not know that the "inflationary model" does not include the moment of creation (this is extremely unlikely) or that the "inflationary model" they are considering is any non-cyclic universe creation model (e.g. the Hawking-Turok instanton model) + the concordance model.

Perpetual Student said:
That seems to be a bit of specious reasoning to me. It appears that either the laws of thermodynamics will be repeatedly violated under the cyclic model or violated all at once under the "singularity" senario.
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It seems to me that if a law of thermodynamics or physics does not exist then it cannot be violated. You seem to be adding another assumption to your scenario, i.e. that that the laws of physics are still in existence despite there being no time or space.

But if you are correct then the conclusion is:
  • Universe origin theories which have them created once from a "singularity" violate the laws of thermodynamics. These theories are probably incorrect.
  • Cyclic universe theories which have a recycled universe violate the laws of thermodynamics. These theories are probably incorrect.
This leaves other non-singularity universe origin theories (instanton, etc.) as the "probably correct" theories.
 
Perpetual Student said:
Without time, there can be no causality. So, if time had a beginning, how was the beginning caused?
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You are thinking within the material confines of a finite, albeit expanding universe. Just as a pupa or chrysalis is bounded by the walls of its cocoon and is unable to conceive of its transformation into a butterfly beyond its cosy walls, we seek to make sense of that which we cannot perceive nor understand.

Time is illusory, it is a fallacious and non relative concept, but a convenient way of ordering our classical universe. As physical beings, in a material world, we ascribe meaning to our existence based upon classical laws applied to our macro universe.

If we want to think big, we should be thinking in terms of the very small.

Outside of 'time', outside of any number of multiverses, and inside our own - the very fabric of reality is omnipotent, omniscientific, and acausal.
 
Jiddu said:
Outside of 'time', outside of any number of multiverses, and inside our own - the very fabric of reality is omnipotent, omniscientific, and acausal.
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Very poetic, but I have no idea what it means.

Belz... said:
Why not ?
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Because all the evidence for it is kind of circumstantial. What's necessary for it to have occurred was a period when the energy density of the universe was dominated by a special kind of dark energy component - one with a density much, much larger than the one we measure today. That's perfectly consistent and possible theoretically, but we have little evidence to constrain what sourced that energy.

In a nutshell: there's lots of evidence that inflation occurred, but little on what caused it.
 
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