There's quite a bit of evidence that the Big Bang did happen mostly as described. Science says little about what may have existed before that, but the math for the BB works for our space-time continuum.
Read about cosmic bubbles, gauge symmetry. Listen to Sean Carroll (for his Physics expertise). Read or watch Brian Greene. Check out "Closer to Truth" video series.
There's a lot we don't know. Richard Feynman equated Physics to Chess. You don't know all the rules until you encounter them.