What Happens to Matter and Energy at the End of the Universe?

[misskitty]

Well, seems as though we are eventually screwed either way. Hmm, all the more reason to live life to the fullest.

 

[moving finger]

In section five they show that in the special but plausible deSitter case of general relativity, a slight vacuum energy, caused by a small cosmological constant, is "unstable toward inflation". Fluctuations from average behavior will tend to fall into inflation states. And they show that inflation pumps entropy into the universe, providing that arrow of time they mention. And of course this gives a sort of anthropic reason for that small cosmological constant (which has been measured from the CMB but which is regarded as a problem for theory); we see the c.c. as positive but small because that is what it had to be in order to produce the arrow of time, which in turn was necessary for the physics, chemistry, and evolution which produced us.

Thank you! I see it now.
I was stuck in terms of thinking of a finite phase space and coudn't get my head around how eternal inflation managed to reduce entropy at some stage - but I see my error now. Eternal inflation does not reduce entropy; the total entropy of all the "universes" created continues increasing, but the phase space of the "ensemble" of universes is unbounded, hence entropy can keep increasing without limit, even though there is a maximum possible entropy for anyone universe.

Not sure I agree that the c.c. in our universe has to be non-zero to produce an arrow of time however - I agree in the paper the non-zero c.c. is the reason why a "parent universe" might produce a "daughter universe" by spontaneous inflation, but does that necessarily mean every "daughter universe" (including ours) must therefore have a non-zero c.c.? Is the value of the c.c. carried over from parent to daughter?

MF

 

[moving finger]

if omega is under 1, then the universe will endlessly expand (because the expansion is too great for deceleration or something like that) and will suffer a heat death. if it is over one, the universe will suffer a big crunch, the big bang in reverse. if one, than the universe will be critical density, and i don't know what that is. I got that almost directly from the book "the big shebang", so if i am wrong, don't yell at me.

Regards,
Fabinacci

Not quite correct. Your interpretation is based on the "old" version which assumes a zero cosmological constant (lambda). If lambda is zero then it is only the energy density (of matter plus radiation) which determines omega, and there is then a simple relationship between omega, "flatness" and whether we expand forever or recollapse.

However if lambda is not zero (and there is mounting evidence that lambda is non-zero and positive) then there is no longer a simple relationship between omega, "flatness" and crunch/expansion.

The important parameters are the energy density of matter/radiation (rho.m), the energy density due to the vacuum (vacuum energy, rho.v), and the relationship between vacuum energy density and vacuum energy pressure (p.v).

If rho.v = -p.v (and that seems to be a likely equation of state for vacuum energy), then even a "closed" universe would expand forever if rho.m < 2 x rho.v at any time when H approaches zero; and an "open" universe would recollapse if rho.v < 0.

The conclusion is that it is mainly the vacuum energy density and equation of state, and not (as was thought in the past) geometry, which determines the ultimate fate of the universe.

For more details see http://arxiv.org/abs/astro-ph/9904020

MF

 

[Chronos]

Look at section four and the beginning of section five of their paper. In section four they review Penrose's argument that in a universe with gravity and zero vacuum energy, the evolution inevitable takes you to isolated black holes. Here there are a lot of diagrams to help you follow the argument.

In section five they show that in the special but plausible deSitter case of general relativity, a slight vacuum energy, caused by a small cosmological constant, is "unstable toward inflation". Fluctuations from average behavior will tend to fall into inflation states. And they show that inflation pumps entropy into the universe, providing that arrow of time they mention. And of course this gives a sort of anthropic reason for that small cosmological constant (which has been measured from the CMB but which is regarded as a problem for theory); we see the c.c. as positive but small because that is what it had to be in order to produce the arrow of time, which in turn was necessary for the physics, chemistry, and evolution which produced us.

Brilliant.

 

[Billy T]

Brilliant.

Please someone give clear reference to this paper/ book. If Chronos thinks it "brilliant" I want to at least look at it.

 

[misskitty]

I would like to get a look at what you are all citing as well. If that's alright. I may not comprehend it entirely, but that just means more clarification questions. I hope no one is bothered by that.

 

[moving finger]

Please someone give clear reference to this paper/ book. If Chronos thinks it "brilliant" I want to at least look at it.

Chronos did that already in this thread , it's at ;
http://arxiv.org/abs/hep-th/0410270

Chronos, selfAdjoint, could you comment on the idea that the non-zero cosmoligcal constant (c.c.) we see in our universe may be "responsible" for the arrow of time (in our universe)? (ie an anthropic explanation for the non-zero c.c.)

Does it necessarily follow that the emergence of time in our universe requires a non-zero c.c., and if so, why?

Ta

MF