There was no "before." Time itself did not exist. All the matter, energy, space, and time that would ever exist — every galaxy, every atom, every photon — was compressed into a point of infinite density and zero volume. The laws of physics break down. General relativity predicts a singularity. Quantum mechanics forbids it. Both cannot be right. At T = 0, something happened that created everything from nothing. We call it the Big Bang — but it was not an explosion in space. It was an explosion of space itself.