The Arrow of Time in Our Universe

The reason that there's an arrow of time in our universe turns out to be pretty subtle. If you take the symbol that represents time, we usually call it T and replace it with minus T, you always end up with another solution that's acceptable to those equations. In other words, if they allow something to happen in one direction of time, it could also happen equally well in the opposite direction of time. So today on our show, Dan and I are going to talk about what it is exactly about the laws of physics that ensures that time really does move in one direction.