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Tuesday, September 18, 2012

The Big Crunch - rebirth of a universe.

Tie one end of a bungee cord to your leg, the other end to the rail of a bridge and then jump off. You'll accelerate downward rapidly until you begin to stretch the cord. As tension increases, the cord gradually slows your descent. Eventually, you'll come to a complete stop, but just for a second as the cord, stretched to its limit, yanks you back toward the bridge. Astronomers think a closed universe will behave in much the same way. Its expansion will slow down until it reaches a maximum size. Then it will recoil, collapsing back on itself. As it does, the universe will become denser and hotter until it ends in an infinitely hot, infinitely dense singularity.
A closed universe will lead to a big crunch -- the opposite of the big bang. But what are the odds that a closed universe is more probable than an open or flat universe? Astronomers are beginning to come up with some educated guesses.
To determine if the universe will expand forever, coast to a stop or collapse on itself, astronomers must decide which of two opposing forces will win a cosmic tug-of-war. One of these forces is the bang part of the big bang -- the explosion that catapulted the universe outward in all directions. The other force is gravity, the pull one object exerts on another. If the gravity within the universe is strong enough, it could reign in the expansion and cause the universe to contract. If not, the universe will continue to expand forever.
But let's imagine for a ­moment th­at the density of the universe is above the critical value required to stop expansion. This would lead to the big crunch, which in many ways would be like hitting the rewind button on a VCR. As gravity within the universe pulled everything back, galaxy clusters would draw closer together. Then individual galaxies would begin to merge until, after billions of years, one mega-galaxy would form.
Inside this gigantic cauldron, stars would meld together, causing all of space to become hotter than the sun. Eventually, stars would explode and black holes would emerge, slowly at first and then more rapidly. As the end drew near, the black holes would suck up everything around them. Even they would coalesce at some point to form a monstrous black hole that would pull the universe closed like a drawstring bag. At the end, nothing would remain but a super-hot, super-dense singularity -- the seed of another universe. Many astronomers think the seed would germinate in a "big bounce," starting the whole process over again.

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