Big Bang Theory...?

The Universe is still expanding. This can be proven by looking at other Galaxies which due to their redshift are moving away from us. The Universe exploded from the Big Bang about 14 billion years ago and it is thought that the Universe will exist for about 5 billion more years, at which time it will start to contract, due to its gravity, and will contract until it is the same size as it was just after the last Big Bang. Once the Universe has fully contracted it will bounce back into yet another Universe. The absolute emptiness outside of the Universe is trillions and many trillions of years old. It is older than you or i can possibly ever imagine!

That's not true. The universe isn't getting smaller, in fact recent observations from the WMAP are consistent with a geometrically flat and expanding universe.

It is hypothesized that if someday gravity overcomes the expansion of the universe, it will pull everything back into a singularity and another Big Bang might occur.

The Big Crunch is just one of the possible ends of the universe, again it relies on te assumtion that someday gravity will overcome the expansion of the universe. I myself don't see that happening since the universe expansion continues to accelerate. I also don't see the Big Crunch happening since the overwhelming majority of the unverse is dark energy, which is responsible for the accelerated expansion of the universe.

Who knows? Who cares?

whoa, I never really thought about it that way before. :]