What is Big Crunch theory?

This theory says the universe will one day stop expanding. Then, as gravity pulls on matter, the universe will begin to contract, falling inward until it has collapsed into a super hot, super-dense singularity. The universe is like a giant souffle. It starts out small, expands as it heats up, and eventually, as the souffle cools, begins to collapse. Big Crunch is the consequence of the Big Bang Theory.