The closed universe model says that expansion will eventually come to a halt and, thereafter, the universe will begin to contract. There is one force that always opposes the expansion of the universe, and that is the force of gravity between the clusters of galaxies. It tries to slow down their separation. There is a tussle between the outward expansion and the inward pull of gravity. If gravity gains the upper hand, its attractive force will rein in the speeding galaxies and bring them to standstill. And then, gravity will draw them all together again. The universe will shrink like a balloon with its air streaming out and eventually contract to end in what is called a Big Crunch. (See, diagram below). It’s the exact opposite of the Big Bang, which stirred the universe. In essence, this means that ours is a closed universe. Alternatively, the universe might be open, like an infinitely large piece of rubber sheet shown in the diagram and in this case it will continue its course of expansion for eternity. In recent years, astronomers have detected a mysterious force acting as dark energy which has repulsive effect. It is accelerating the expansion of the universe. If the dark energy, overpowers the force of gravity, the universe will continue to expand even after the stars and galaxies die.
|The Big Crunch|