If the universe is constantly expanding, how could the big crunch happen ?

Question

If the universe is constantly expanding, how could the big crunch happen ?

In: 6

Answer 1

We don’t know what’s causing the expansion.

We don’t know what’s causing the expansion to accelerate.

Since we don’t know these things, it could turn out that they are cyclical, as many things in physics are cyclical. If the acceleration stopped and the expansion stopped the Universe might start contracting and that contraction might accelerate and it could all end in a Big Crunch.

We need to develop a testable theory that explains expansion. Once we’ve tested it we might be able to make predictions. If our predictions pan out, then it will be time to start answering Heat Death vs Big Crunch and related questions.