Is the expansion of the universe proof of the Big Bang theory?

Or are there other proofs?


In and of itself, no the expansion of the universe is not proof of the big bang. Other theories could be constructed that would also be explained by the expansion. For example Fred Hoyle and others proposed the Steady State Theory which proposed that new matter was constantly being created thus causing the expansion. A the time there was no other evidence for either theory so either could have been true.

However, when you couple the expansion with other evidence such as the cosmic microwave background radiation discovered in 1964 then it does strengthen the case for the big bang being the cause.

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    $\begingroup$ The ratio of hydrogen to helium in the universe is easy to measure, and is exactly what is predicted by the Big Bang theory. $\endgroup$
    – Marc
    May 23 '14 at 1:25
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    $\begingroup$ This is just wrong. The Steady State Theory proposed by Hoyle does indeed predict the random creation of matter out of nothing, but not as a means of explaining the expansion. The reason this was put in the theory was to allow for the universe to remain "steady" (e.g., constant density, etc.) throughout it's infinite existence. Obviously if its expanding, it should get less dense meaning it isn't static and Hoyle disliked that so he proposed that matter is constantly created to make it static. He had no explanation for what caused the expansion. $\endgroup$
    – zephyr
    Oct 28 '16 at 18:01

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