The Big Picture: On the Origins of Life, Meaning, and the Universe Itself

by Sean Carroll

The Big Bang itself, as predicted by general relativity, is a moment in time, not a location in space. It would not be an explosion of matter into an empty, preexisting void; it would be the beginning of the entire universe, with matter smoothly distributed all throughout space, all at once. It would be the moment prior to which there were no moments: no space, no time. It’s also, most likely, not real. The Big Bang is a prediction of general relativity, but singularities where the density is infinitely big are exactly where we expect general relativity to break down—they are outside the theory’s domain of applicability. At the very least, quantum mechanics should become crucially important under such conditions, and general relativity is a purely classical theory. So the Big Bang doesn’t actually mark the beginning of our universe; it marks the end of our theoretical understanding. We have a very good idea, on the basis of observational data, what happened soon after the Bang. The microwave background radiation tells us to a very high degree of precision what things were like a few hundred thousand years afterward, and the abundance of light elements tells us what the universe was doing when it was a nuclear fusion reactor, just a few minutes afterward. But the Bang itself is a mystery. We shouldn’t think of it as “the singularity at the beginning of time”; it’s a label for a moment in time that we currently don’t understand.