https://en.wikipedia.org/?title=Big_Crunch
If the universe is infinite in extent and the
cosmological principle (not to be confused with the
cosmological constant) does not apply, and the expansion speed does not exceed the
escape velocity, then the mutual
gravitational attraction of all its
matter will eventually cause it to contract. If
entropy continues to increase in the contracting phase (see
Ergodic hypothesis), the contraction would appear very different from the time reversal of the expansion. While the early universe was highly uniform, a contracting universe would become increasingly clumped.
[2]Eventually all matter would collapse into black holes, which would then coalesce producing a unified black hole or Big Crunch singularity.
