Time has a beginning?

[Belz...]

That alone is an improvement over the "beginning of time" scenario of some theories.

Really ? You object to BB/inflation but have no problem with cycles initiated BY BB/inflation ???

 

[Belz...]

Anything which cycles forever violates the laws of thermodynamics.

The second, for sure. But the first one is overrated

 

[sol invictus]

How do they get around the 2nd law of thermodynamics (without violating the first)?

They don't. Their description of the behavior of their model in that "FAQ" is not consistent with the laws of thermodynamics.

It is possible for the model to continue inflating forever. But it is not possible for it to continue cycling like that forever. Moreover, I'm pretty sure that any model that's capable of bouncing - which is the defining feature of these cyclic models - violates thermodynamics in other ways. See here.

 

[Perpetual Student]

So, the big bang does not violate the laws of thermodynamics because there were no laws of physics before (or at?) t = 0?

And, the concept of time having a beginning does not violate causality?

It is remarkable that the same people who apply such rigorous analysis to competing ideas can be content with hand waving when supporting their own preferred theories.

 

[Cuddles]

It is remarkable that the same people who apply such rigorous analysis to competing ideas can be content with hand waving when supporting their own preferred theories.

I find it more remarkable that someone who has admitted several times to having no relevant knowledge or expertise, and who says he comes here to ask questions of those who do, spends so much time deriding the people who actually answer his questions instead of thanking them for trying to help improve his understanding. Perhaps you would get more out of this kind of thread if you spent more time trying to understand the answers you get and less time insulting those who give them.

 

[sol invictus]

So, the big bang does not violate the laws of thermodynamics because there were no laws of physics before (or at?) t = 0?

And, the concept of time having a beginning does not violate causality?

I gave you about five specific, concrete examples of how the big bang singularity could be resolved in ways that are consistent with both thermodynamics and causality. You seem to have great difficulty understanding that no one knows which, if any, of those is correct.

The ST model is one such idea, but it fails to be consistent with the laws of thermodynamics (at least the way it's described in that faq).

It is remarkable that the same people who apply such rigorous analysis to competing ideas can be content with hand waving when supporting their own preferred theories.

That certainly doesn't apply to me, because I never said anything of the kind.

 

[Perpetual Student]

What is the prevailing view of the future of time under the consensus cosmological theory? Does time cease at some point?
Does it go on eternally? Does the universe become fully dissipated by dark energy at some time? If so, when the universe is fully dissipated, does the question of time become irrelevant, since nothing happens for the remainder of eternity?

 

[sol invictus]

What is the prevailing view of the future of time under the consensus cosmological theory? Does time cease at some point?
Does it go on eternally? Does the universe become fully dissipated by dark energy at some time? If so, when the universe is fully dissipated, does the question of time become irrelevant, since nothing happens for the remainder of eternity?

There is no prevailing view. As with the putative big bang singularity, the data simply doesn't suffice to determine that with any certainty.

Still, there is a simplest possibility - that dark energy is a cosmological constant. In that case the future is inflation. Classically, the space will expand exponentially forever. All forms of matter and energy will dilute exponentially to zero. Very "soon" (a few hundred billion years), nearly all of the space will be empty. Galaxies and clusters (full of dead stars) will remain bound forever, but will separate from each other more and more, and the space in between clusters will become exponentially more and more empty.

Quantum mechanically, things are more interesting. If dark energy is a true cosmological constant there will never be a complete heat death, because there is always Hawking radiation from the de Sitter horizon. There is no real asymptotic future in that case, because all possible events will eventually recur, and recur again, ad infinitum.

 

[Perpetual Student]

...
Quantum mechanically, things are more interesting. If dark energy is a true cosmological constant there will never be a complete heat death, because there is always Hawking radiation from the de Sitter horizon. There is no real asymptotic future in that case, because all possible events will eventually recur, and recur again, ad infinitum.

I am not sure I understand what you are saying in the bold part above. As I understand it, Hawking radiation is a very slow process by which black holes "evaporate." By "all possible events" are you including galaxy formation or another big bang, for example?

 

[Belz...]

Very "soon" (a few hundred billion years), nearly all of the space will be empty. Galaxies and clusters (full of dead stars) will remain bound forever, but will separate from each other more and more, and the space in between clusters will become exponentially more and more empty.

I was under the impression that, at one point, accelerating expansion would eventually counteract gravity and other forces.

 

[sol invictus]

I am not sure I understand what you are saying in the bold part above. As I understand it, Hawking radiation is a very slow process by which black holes "evaporate."

There is radiation very similar to Hawking radiation from black holes emitted from any horizon.

By "all possible events" are you including galaxy formation or another big bang, for example?

Yes, in principle - but to be sure of the second we'd need a more controllable theory of quantum gravity.

I was under the impression that, at one point, accelerating expansion would eventually counteract gravity and other forces.

I'm not quite sure what you're asking. If there is dark energy (modulo some more complex possibilities) and it persists, it will dominate the energy budget of the universe more and more as time goes on, which means the universe's expansion will accelerate forever.

 

[Cuddles]

I'm not quite sure what you're asking. If there is dark energy (modulo some more complex possibilities) and it persists, it will dominate the energy budget of the universe more and more as time goes on, which means the universe's expansion will accelerate forever.

I assume he's referring to the Big Rip hypothesis.

Belz - the problem of the ultimate fate of the universe depends on the nature of dark energy. If dark energy is equivalent to a cosmological constant then, as Sol says, graviationally bound structures will remain bound but will become separated from each other. A Big Rip only happens if dark energy is of a more extreme form.

The type of dark energy and eventual fate of the universe depends on the equation of state. At the moment, we think w in that equation is close to -1, which means a cosmological constant. If it turns out to be less than -1, we get a big rip. If it's actually higher than -1/3, the expansion of the universe isn't accelerating at all.

 

[Belz...]

What I was asking was that: if the universe's expansion is accelerating, wouldn't it eventually unbond stuff that are gravitationally bound ? And eventually all the rest as well ? I thought I read that somewhere...

 

[Perpetual Student]

If dark energy is a true cosmological constant there will never be a complete heat death, because there is always Hawking radiation from the de Sitter horizon. There is no real asymptotic future in that case, because all possible events will eventually recur, and recur again, ad infinitum.

Would that not violate the laws of thermodynamics?

 

[sol invictus]

What I was asking was that: if the universe's expansion is accelerating, wouldn't it eventually unbond stuff that are gravitationally bound ? And eventually all the rest as well ? I thought I read that somewhere...

I think classically (i.e. without quantum mechanics) no, that won't happen. But with QM it will, because gravitationally (or otherwise) bound particles can tunnel to an unbound location and escape. But the time scale is absurdly long.

Would that not violate the laws of thermodynamics?

Just the opposite - it's the laws of thermodynamics (or more precisely, statistical mechanics) that tell us that must happen. The difference with a cycling universe is that these recurrences are random, each is totally different from the previous, and the time between them is very, very long.

 

[Perpetual Student]

I find it more remarkable that someone who has admitted several times to having no relevant knowledge or expertise, and who says he comes here to ask questions of those who do, spends so much time deriding the people who actually answer his questions instead of thanking them for trying to help improve his understanding. Perhaps you would get more out of this kind of thread if you spent more time trying to understand the answers you get and less time insulting those who give them.

My comments are sometimes intentionally provocative and, at times, aggressive in order to clear up apparent contradictions and stimulate discourse. My comments are not intended to be "insulting." If anyone has been insulted, I am sorry.

 

[Perpetual Student]

The difference with a cycling universe is that these recurrences are random, each is totally different from the previous, and the time between them is very, very long.

So, in the very long term, say, trillions of years, the whole thing is winding down and these recurrences will cease, or is it something like the primes, thinning out but infinite?

 

[sol invictus]

So, in the very long term, say, trillions of years, the whole thing is winding down and these recurrences will cease, or is it something like the primes, thinning out but infinite.

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.

 

[Belz...]

I think classically (i.e. without quantum mechanics) no, that won't happen. But with QM it will, because gravitationally (or otherwise) bound particles can tunnel to an unbound location and escape. But the time scale is absurdly long.

Oh. I thought that, if the expansion kept accelerating, it just became a stronger "force" that exceeded the force of gravity, for instance, and pulled galaxies apart.

 

[Beerina]

The statement "time has a beginning" is either true or false, but by itself I don't really see how it could be nonsensical.

Nobody should fault you for not believing that time had a beginning. The current theories aren't strong enough to make a statement about whether time began at some point. Our theories aren't strong enough to make statements about time before the singularity. That's not the same thing as proving time didn't exist before the singularity.

People view the issue the way Robert Heinlein viewed the speed of light -- why not just get your ship right up close to it, then give 'er the gun!

It was "stupid" that you'd just donk against some limit.


Rather, time could rotate around into a physical dimension. Or who knows what it gets warped into as you go back in time towards a singularity. There is precedence for this since, IIRC, relativity points out that acceleration and gravity aren't just similar phenomena, but are the exact same phenomena, with gravity being you being "accelerated, but not accelerated" through a warped 4-D spacetime continuum. You have to maintain overall c as your speed through this continuum, so you have to kind of accelerate but you aren't moving through any of the 3 spacial dimensions. Or something. I never got too deeply into this part. (Any links to it? Do want.)