Question

What is the big crunch

Answer 1

The Big Crunch is one possible scenario for the ultimate fate of the universe, in which the metric expansion of space eventually reverses and the universe recollapses, ultimately causing the cosmic scale factor to reach zero or causing a reformation of the universe starting with another Big Bang

Answer 2

The 'Big crunch' is a theory wherein the Universe is going to contract each second and at last it comes to the 'beginning of the Universe' situation and then contracts into nothingness. But this theory is proved wrong by the astronomers as the Universe is expanding every single minute.

Hope it helps!!