Oscillating Universe?

[Zero]

I've heard talks about a speculation that our universe oscillates, expanding from a singularity, and contracting, and then expanding again. Is there any credence to this? What's the evidence/logic for and against this idea?

[Lord Zentei]

The idea that the universe might be oscillating is an extension of the Big Crunch scenario where the gravity of the various objects in the universe is sufficient to stop the expansion and cause it to contract into a singularity again. Basically it was an attempt to eliminate the problem of what "caused" the Big Bang, in this scheme the universe is eternal even though it's various incarnations are not.

The oscillating universe is no longer the scenario that is thought to apply to our universe as the expansion is accellerating due to the mysterious "dark energy", and not slowing down.

[Zero]

Are there any who maintain that the current trend of expansion will eventually stop? Are there any who still believe in the oscillating universe theory?

[Lord Zentei]

Are there any who maintain that the current trend of expansion will eventually stop? Are there any who still believe in the oscillating universe theory?

Well the possibility that Dark Energy is unstable has been raised, which would allow for the possibility of either a Big Rip or a Big Crunch (and possibly oscillation). However, there is nothing (yet) that suggests that this is the case, so the null hypothesis is that DE is constant. Of course, that doesn't prevent speculations taking place.

At present there are a whole lot of exotic hypotheses floating around. One of these is that our universe is on one of many hypermembranes in a higher dimensional space, and that when two such membranes collide, they experience a big bang. I wouldn't be surprised if more oscillation type hypotheses are out there, but the current benchmark model is not oscillating.

[Edi]

You could regard the cycle of Big Bang -> heat death -> quantum probability manifestation of another Big Bang/other universe birth mechanism as oscillation, but that idea is no official theory that I know of, just something I think I read about somewhere as speculation.

I think the idea was that once heat death reduces the universe to a void and a few stray particles, quantum probabilities will eventually give rise to circumstances that could conceivably bring about the birth of a new universe. Some new writing on a slate that had finally ben wiped clean as it were. The new universe would likely be perceived in the same manner as we do ours, i.e. impossible to observe what came before.

If there is anybody around that knows more about this subject and can comment on this, I'd be interested in hearing it.

Edi

[Kuroneko]

I've heard talks about a speculation that our universe oscillates, expanding from a singularity, and contracting, and then expanding again. Is there any credence to this? What's the evidence/logic for and against this idea?

The logic behind this is simple, or rather simple-minded. In the closed Friedmann-Robertson-Walker universes, a given spherical volume expands and then contracts to zero. Solving for the radius gives an equation in time which just happens to be periodic. That is the only evidence for an oscillating universe.

You could regard the cycle of Big Bang -> heat death -> quantum probability manifestation of another Big Bang/other universe birth mechanism as oscillation, but that idea is no official theory that I know of, just something I think I read about somewhere as speculation.

A theory of universe-causing vacuum fluctuation has been proposed by Edaward "our Universe is simply one of those things which happens from time to time" Tryon. There are other incarnations of the of this kind of loosely interpreted 'oscillating universe', such as that ekpyrotic theory in which 'Big Bangs' are periodic collisions of branes. None of them are really mainstream science. There may be others, but none that spring to mind offhand.

[Durandal]

Given that the universe's expansion is accelerating and, by all indications, will continue indefinitely, the idea of a Big Crunch seems exceedingly unlikely.

[Ou des]

Well the possibility that Dark Energy is unstable has been raised, which would allow for the possibility of either a Big Rip or a Big Crunch (and possibly oscillation).

What's a Big Rip?

[Xon]

Well the possibility that Dark Energy is unstable has been raised, which would allow for the possibility of either a Big Rip or a Big Crunch (and possibly oscillation).

What's a Big Rip?

Space is constantly expanding, the Big Rip is when the expansion crosses a threshhold and matter just falls apart as the distance between atoms is too great for electromagntic force to hold complete molecules together.

Or thats too great for the strong nuclear force to hold the sub-atomic particles together as an atom.

Either way, the material universe just ends.

[Lord Zentei]

Well the possibility that Dark Energy is unstable has been raised, which would allow for the possibility of either a Big Rip or a Big Crunch (and possibly oscillation).

What's a Big Rip?

The Big Rip scenario involves an accellerating accelleration of cosmic expansion.

Basically, if the accelleration of the cosmic expansion is constant (as it is currently thought to be) it won't destroy any bound objects (such as atoms, people, planets and galaxies) since their size is determined by a balance of forces: add a constant accelleration, and you effectively add a constant force that causes said objects to reach a new equilibrium size.

For instance, you are very slightly shorter than you would be in space since you have gravity compressing you. The dark energy that causes space to expand causes you to be very slightly larger. The effect of the DE upon our size is microscopic compared to that of the Earth's gravity, but unlike the "normal" attractive gravity of matter, DE does not diminish with distance, so it overpowers it at intergalactic ranges, hence the accelleration at that scale (the galactic clusters and stuff in them hold together, but they fly apart at an ever greater clip).

In the Big Rip scenario, DE grows stronger with time, and thus this stretching increases with time and the range at which it overpowers the attractive gravity of matter grows less and less. Ultimately, all things are torn apart down to the subatomic level in a catastrophic end-of-time.