The Big Bang theory is actually falling apart. Latest fad in physics is poking holes in it.
Actually the big bang theory is not falling apart. It has just become incorporated into a larger theory. The Big bang theory was proposed because it explains the observable evidence (cosmic background radiation and expansion of the universe) The big bang theory only goes back to the singularity but could not explain what happened before. The multiple universe theory still says the big bang happened but attempts to explain what happened before it. Not saying that it is correct by the way but it does fill in a lot of gaps left by other theories, such as why is gravity as weak a force as it is in the universe.