TIME moves forward.
TIME moves forward. This is so obvious that we take it for granted, and the rule seems to apply everywhere we look. Observable phenomena only ever unfold in one temporal direction. We get older, not younger. We remember the past, not the future. Stars clump in galaxies rather than dispersing, and radioactive nuclei decay rather than assemble. The big question is, where does this forward-facing arrow of time come from? The most popular explanation relates to entropy. In this picture, the flow of time is essentially a manifestation of the universe’s inescapable inclination towards disorder. I have a different idea, or rather two. The first is that time goes both ways – that the big bang isn’t an origin for time, but a midpoint from which two parts of one universe play out, running in opposite directions. We can never see the one unfolding in the other temporal direction, yet it is there, I suggest, as a consequence of a fundamental law of nature. My second idea is even more radical. I...