Why is the Big Bang theory the most widely accepted theory of the creation of the universe?

The Big Bang theory nicely explains the expansion of the universe (discovered by Hubble in the 1920's). Obviously, that the universe is expanding suggests that it was a good deal smaller in the past. Likewise, the Big Bang theory nicely explains the cosmic microwave background radiation (detected by Penzias and Wilson in the 1960's, and predicted by Wilkinson and Dicke before that). This pervasive, pretty uniform, low-temperature radiation suggests that the universe was considerably hotter in the distant past. The rival "steady state" model of the universe has difficulty explaining these observations.

However, the "Big Bang theory" is no longer a single theory. Various alternative Big Bang models have been developed (such as the "inflationary" Big Bang theory) to account for additional facts that have been discovered (such as the value of omega, the ratio of the universe's total kinetic energy of expansion to its gravitational potential self-energy, which tends to slow down the expansion). At the moment, there is no serious rival to some sort of Big Bang model.

Finally, the Big Bang theory fits nicely with the general theory of relativity, according to which space and time are not some sort of unvarying stable stage on which the acts of the universe's history play out, but rather are themselves dynamic actors. The Big Bang is supposed to be the "creation of the universe" where the "the universe" includes space and time.

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