The Expansion of the Universe
In the very early universe (when it was 1 second
the outward expansion enery and the inward gravitational energy
were in balance to a precision of
1 part in 1,000,000,000,000,000 (1015)!
If the expansion energy then was slightly larger,
the expansion would have been too fast
for stars and galaxies to clump together.
If the gravitational energy then was slightly
the expansion would have been too slow ---
the expansion would have reversed itself long ago
and the universe would have already ended in a Big Crunch.
Fortunately for us, the Big Bang expansion was
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