Oddly enough, the Big Bang isn’t a simple as a big explosion happening somewhere, followed by all the matter of the universe flying away like shrapnel. This happened around 400,000 years after the big bang, which seems like a lot, but it’s only about 0.003% of the universe’s current age. Most of the other evidence for the big bang is a bit more complicated and circuitous. For example, cosmological computer models that describe how galaxies form and move tend to work very well using the big bang as a starting point, and tend to work not even a little otherwise. You’d be hard pressed to find a cosmologist who disagrees that the big bang happened, and just as hard pressed to find two who agree on all the details.