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of the expansion of the universe. Ordinary ('baryonic') matter therefore composes only of the universe. Stars, planets, and visible gas clouds only form about 6% of this ordinary matter.

There are many competing hypotheses about the ultimate fate of the universe and about what, if anything, preceded the Big Bang.

Definition

The physical universe has been defined as "The totality of all space and time; all that is, has been, and will

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