I'm not sure what forum to post this in but I do remember picking up on an idea that is that once the Universe stops expanding it will start collapsing and the big-crunch will end the Universe. I don't believe that many people felt that this theory was credible like 10 years ago but that was before we found out about all this stuff about dark matter and dark energy and how Space Time is always expanding. Will there be a time when the Universe loses the force required to keep expanding, and, then, starts to contrast? And how long would it take for the Universe to come back together in the form of a big crunch after that?

Originally posted by Frankidealist35
Will there be a time when the Universe loses the force required to keep expanding, and, then, starts to contrast?

There are three possibilities:

1. The universe keeps expanding infinitely.
2. The universe keeps expanding, but never more than a certain size.
3. The universe starts to contract and crunch.

No one even knows which of these three is right, and we need more measurements about the amount of matter that we have. The problem of vacuum expansion is coming into play as well, so if it is a crunch, we have a long way to go before we know when that happens.

And how long would it take for the Universe to come back together in the form of a big crunch after that?

Without vacuum expansion: If we know the time from the start of the universe to the point where it starts to contract, you just double that time for the whole period of the universe because of symmetry. So the time from the start to the turnaround is the same as the time from the turnaround to the crunch.

With vacuum expansion: A little while longer than the above.

[edit on 21-8-2008 by redled]

Originally posted by Frankidealist35....I don't believe that many people felt that this theory was credible like 10 years ago but that was before we found out about all this stuff...

Actually, 10 or 15 years ago, MORE astrophysicists believed in a future "Big Crunch".

However, recent measurements of the amount of matter in the universe seems to be pointing toward the idea that the universe will NOT eventually collapse in on itself.

The new measurements suggest that there is not enough matter (and thus gravity) in the universe to hold it all together, thus it may expand forever, gowing colder and colder as the galaxies and stars grow further and further apart, until the universe is a big, cold, lonely, "sparse" place.

Yes I think the most likely end will be the 'Big Freeze' scenario where the universe expands so much there isn't enough energy left in to stop it all reaching absolute zero. If this happened, all particle motion would cease and essentially the universe would just degrade into nothing.

Uplifting thoughts!

Keep asking these kinds of questions!
We dont get any further along without the tuff questions like this.

Does it end? does it start? what kind of cycles make up a universe?
As its known we are not the only universe.

How big is the universe really? Are we just part of something greater, and that is part of something even greater? .3333333

Speaking in terms of math, its a problem without an answer.
its one of those repeatable solutions, something we humans do not understand yet. And Ive found most people dont want to know these things.

We never did ask WHY did the apple fall, we only know how fast, and at what speed the apples falls.. We still have not figured out why gravity works, and how it works.

A big crunch, a big bang. Neither have been proven, nor can they be proven with fundalmental human logic.
Our minds set perameters, that logic can not escape.

If the Big Crunch scenario is the untimate fate of the universe, and that the universe contracts back upon itself billions of years from now, wouldn't it be true then that time will reverse as well?

It got me thinking, wouldn't that mean that eventually - in the distant future, billions of years from now, long after our deaths, every human being who has ever lived will eventually live their life in reverse?

I wonder if we would be aware of the process.