Acting alone, gravity would cause stars to collapse completely, but as long as energy is produced at their centers by nuclear fusion (the joining of atomic nuclei to form new elements, as in a hydrogen bomb), the star is heated and puffed up.

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The cosmos was born in the Big Bang about 13.7 billion years ago, and the first stars in the universe are thought to have lit up about 100 million years afterward, when gas finally gathered in clumps dense enough to collapse under their own gravity and ignite nuclear fusion.

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These possible universes will first expand, and then contract and collapse again under the pull of gravity.

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Eventually, however, gravity ensues and the constraints outlined herein raise their head, resulting in a collapse to point C.

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