Firstly, I didn't say the big bang theory is the only plausible theory. But if there was ANYTHING that gave the BB theory ANY credibility at all, it would instantly be many many more times probable than the existence of an Easter Bunny (even though I cant disprove the Easter Bunny).
Here is just a small sample of some of the supporting evidence for the BB theory:
First of all, we are reasonably certain that the universe had a beginning.
Second, galaxies appear to be moving away from us at speeds proportional to their distance. This is called "Hubble's Law," named after Edwin Hubble (1889-1953) who discovered this phenomenon in 1929. This observation supports the expansion of the universe and suggests that the universe was once compacted.
Third, if the universe was initially very, very hot as the Big Bang suggests, we should be able to find some remnant of this heat. In 1965, Radioastronomers Arno Penzias and Robert Wilson discovered a 2.725 degree Kelvin (-454.765 degree Fahrenheit, -270.425 degree Celsius) Cosmic Microwave Background radiation (CMB) which pervades the observable universe. This is thought to be the remnant which scientists were looking for. Penzias and Wilson shared in the 1978 Nobel Prize for Physics for their discovery.
Finally, the abundance of the "light elements" Hydrogen and Helium found in the observable universe are thought to support the Big Bang model of origins.
Like I said.... I have serious doubts whether or not the Big Bang theory is absolutely correct. There is no way of knowing for sure at this point, andI am not even a physicist. Heck, from my understanding, even Einstein was wrong! lol