So, why does time flow in one direction only, why doesn’t it go the other way?  There is nothing in the equations that describe how the universe works that says time has to have an arrow.  Typically what is time’s arrow is justified by cause and effect and by the lack of reversibility.

You drop a plate on the floor and it shatters.  The plate hitting the floor is the cause of the shattering, the plate falling is the cause of it hitting the floor and a combination of you dropping it and gravity is the cause of it falling.  Cause and effect and the idea that it can’t go backwards gives time its direction.  The “flowing backwards” part, you know, the plate spontaneously reassembling and jumping up to your hand, in physics is part of entropy.  The universe has a tendency to become more random, less structured.  It can be reversed in a location by adding energy, but you can’t add anything to the Universe as a whole, so entropy increases, i.e., time marches on.

But what about those bundles of reverse entropy called “humans”? Continue reading →