In the pre-Beginning

via

"Questions about a time before the big bang were once thought to be meaningless, because according to Einstein's general theory of relativity, the universe began at a singularity - a mathematical point with infinite density at which all calculations break down.

"However, physicists now believe that the theory of relativity is limited and the effects of quantum mechanics would have blurred out the singularity just a little, so at a crucial moment the density of matter and radiation was not infinite. If this was the case, it becomes possible to try to work out what led up to that moment."