heat death of the universe, page-8

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.