NASA/Adboe Stock/ Ryan Wills
Our universe is expanding, so it must have been smaller in the past. Indeed, if we rewind our cosmological movie, we see the universe shrinking back almost to a point – the big bang – some 13.8 billion years ago. Is this when time began? Alas, things aren’t so simple. Albert Einstein’s general theory of relativity tells us that the backdrop of the universe is a fluid continuum, space-time, in which neither space nor time has an absolute meaning. What’s more, at the big bang, space-time distorts into a point of infinite density called a singularity. We can’t say this…
