**Ask a monkey a physics question thread**

[NightGizmo]

Wait... if the expansion of the universe is accelerating, how can it be asymptotically limited in size?

[MadMojoMonkey]

I'll get back to you after work. Lunch break over.

[OngBonga]

I really don't like the continually expanding universe model. It implies that the big bang was a one off. I don't think one offs happen.

I like this concept of a perpetual motion universe. I can get on with the idea of big bang, followed by expansion until gravity overwhelms, followed by big crunch, until singularity, then big bang etc. The problem here is the rate of expansion should be slowing down, but as I understand it the opposite is happening.

I'm sure we've discussed this already in this thread, but I like the donut universe model, one in which expansion and contraction are simultaneous, and one in which the big bang is a constant event at the centre of the universe.



I have no idea how much scientific credibility such a model has, but it's balanced and perpetual. I really have a problem with a "beginning" to our universe, because the concept of a "beginning" is inherently tied to our human concept of time. I prefer to think of the big bang as the centre, rather than the beginning. It's merely the beginning of our time.

[MadMojoMonkey]

I really don't like ...

I like ... I can get on with ...

The problem here is the rate of expansion should be slowing down, but as I understand it the opposite is happening.

I'm sure we've discussed this already in this thread, but I like ...

I have no idea how much scientific credibility such a model has, but it's balanced and perpetual. I really have a problem with ... because ... I prefer ...

Yeah... this motivates science, but it is not science.

The universe is less intuitive to understand the farther you remove your observations from everyday life. When you look at the extremely tiny, or the extremely large, or vast or massive... intuition proves to be a poor guide.

[MadMojoMonkey]

Wait... if the expansion of the universe is accelerating, how can it be asymptotically limited in size?

The problem is that we do not know much about dark energy at all. We think we know that the universe started with the Big Bang, then gradually expanded for a while. Then it underwent expansion. Very little is known about this, but it makes sense of some observations about the large-scale structure of the universe. Then the expansion ended and the universe began to slow down in it's rate of expansion.

Now it's accelerating again.

If it keeps accelerating, then it's Heat Death for the universe, which is the idea that if gravity loses the fight and the universe keeps expanding, eventually all the stars will burn out, all the galaxies will spin apart, all the Black holes will have evaporated... and nothing but a thin atmosphere of ever-cooling atoms is left.

Bottom line is that we just don't know the time-dependent nature of dark energy.

***
The notion that the universe is flat from a GR perspective is perhaps in question. That statement is based on the value of the cosmological constant... which is presumed to not change in time, and thus constant... but it is not clear whether or not Einstein's cosmological constant is the whole story behind dark energy.

[NightGizmo]

If it keeps accelerating, then it's Heat Death for the universe, which is the idea that if gravity loses the fight and the universe keeps expanding, eventually all the stars will burn out, all the galaxies will spin apart, all the Black holes will have evaporated... and nothing but a thin atmosphere of ever-cooling atoms is left.

Is "Heat Death" the new name for "Big Chill"/"Big Freeze"?