Death of Universe: Is a New Big Bang Possible?

[Tanelorn]

Ben, point taken, just trying to be humourous. Gallows humour actually after finally accepting the predicted death of the universe.


"Ours, however, is most likely to undergo heat death and remain that way forever, even if it does spawn new universes."

Thanks Chalnoth so the final outcome remains pretty grim.



"That seems to me a pretty tall order."

I understood that dark energy has already changed once during the history of the universe. I believe I read that it started increasing about 7B years ago, unless I misunderstood something?
So I was just asking if there is any reason why, in the very distant future, dark energy could not start changing again?

 

[Chalnoth]

I understood that dark energy has already changed once during the history of the universe. I believe I read that it started increasing about 7B years ago, unless I misunderstood something?
So I was just asking if there is any reason why, in the very distant future, dark energy could not start changing again?

There isn't any reason to believe this is the case. If dark energy really is a cosmological constant, its value was simply irrelevant until a few billion years ago, but there's no reason to believe it changed.

 

[Tanelorn]

Thanks For clearing that up Chalnoth, I must have misinterpreted something I read about a change in dark energy about 7B years ago.

Also I think I may have been guilty of somehow still wanting the universe to end by eventually returning everything to its initial conditions. It seems more elegant for all matter energy space and time to return to inital conditions, perhaps like conservation of energy or an electron positron pair being spontaneously created and destroyed. There is no possibility of an opposite process to inflation to achieve something like this?

 

[Chalnoth]

It seems more elegant for all matter energy space and time to return to inital conditions, perhaps like conservation of energy or an electron positron pair being spontaneously created and destroyed. There is no possibility of an opposite process to inflation to achieve something like this?

Seems unlikely. I mean, if you want to wait for some obscene number of years, it will happen. But counting on simple recurrence doesn't solve the entropy problems. You need to have an alternative pathway to producing new regions of space-time to make the entropy make sense.

 

[MathematicalPhysicist]

This essentially means eventually the energy will be spread out evenly, it is currently thought that this will lead to http://en.wikipedia.org/wiki/Heat_death_of_the_universe" in about 10¹⁰⁰ years.

A long time to falsify a theory.

 

[Chalnoth]

A long time to falsify a theory.

Well, it's not a theory. It's a conclusion based upon our knowledge of the theories of physics. It isn't absolutely necessary to test each end every conceivable conclusion of a theory to be confident in its veracity.

 

[MathematicalPhysicist]

Well, it's not a theory. It's a conclusion based upon our knowledge of the theories of physics. It isn't absolutely necessary to test each end every conceivable conclusion of a theory to be confident in its veracity.

Indeed, upon our current theories, as every empirical science things may change in the years to come in our perception of nature.

In a class I took as an undergrad, our teacher of QM 2, in the last lecture showed us a calculation that even according to QM (before QFT) the universe shouldn't have gone so far, in fact it should have collapsed in a matter of a few seconds.

So to me asserting how many years does the universe have before it enters a heat death is a little bit like believing in fairytales.

I believe I am becoming a pragmatist in my views.

 

[Chalnoth]

Indeed, upon our current theories, as every empirical science things may change in the years to come in our perception of nature.

While this is true, the ways in which theory would have to change to change the conclusion of heat death are rather unlikely. Basically, in order to avoid heat death you would need:
1. The dark energy to be composed of some sort of dynamical field that will, at some point in the future, start to degrade in energy density quite rapidly (so far, it has stayed constant or nearly so).
2. The spatial curvature of our universe to be slightly positive.

The second point is basically 50/50 given current knowledge, but the first requires extremely contrived models of dark energy, and is thus pretty unlikely.

In a class I took as an undergrad, our teacher of QM 2, in the last lecture showed us a calculation that even according to QM (before QFT) the universe shouldn't have gone so far, in fact it should have collapsed in a matter of a few seconds.

I'd like to know what line of reasoning he was using here. But, suffice it to say, this sort of thing depends quite strongly upon high-energy physics far beyond what we have been able to test in the lab so far, so it is somewhat foolish to draw conclusions there. The heat death of the universe, however, does not depend upon anything that isn't well-tested in the lab, except for the nature of dark energy and the spatial curvature.

 

[Tanelorn]

"So to me asserting how many years does the universe have before it enters a heat death is a little bit like believing in fairytales. I believe I am becoming a pragmatist in my views."


So far, so good, as they say.