Big Crunch

In physical cosmology, 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 ending as a black hole singularity.
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The theorised demise of a closed universe . If the universe contains enough mass to halt the Hubble flow and reverse its expansion, all the matter contained within it will be drawn together by the force of its mutual gravitational attraction. This collapse will cause the matter to be concentrated in an ever decreasing volume with densities and temperatures reaching those which were reached in the big bang. Some ambitious ideas suggest that, since a big crunch would match the conditions of the big bang, perhaps it would cause another phase of expansion and the universe would begin again. This concept is known as the oscillating universe.