It's not Boltzmann's Brain:
It's Boltzmann's Bang:
Edge: WHY DOES THE UNVIERSE LOOK THE WAY IT DOES: A Conversation With Sean Carroll: I read papers by Huw Price, who is a philosopher in Australia... who... said that cosmologists are completely fooling themselves about the entropy of the universe. They are letting their models assume that the early universe had a low entropy.... But there is no such asymmetry built into the laws of physics. The laws of physics at a deep level treat the past and the future the same. But the universe doesn't treat the past and the future the same. One way of thinking about it is, if you were out in space floating around, there would be no preferred notion of up or down, left or right. There is no preferred direction in space. Here on earth, there is a preferred notion of up or down because there is the earth beneath us. There is this dramatic physical object that creates a directionality to space.... Likewise, if you were in a completely empty universe, there would be no notion of past and future.... The reason we find a direction in time here in this room or in the kitchen when you scramble an egg or mix milk into coffee is... because we live in the aftermath of some influential event, and that event is the Big Bang. The Big Bang set all of the clocks in the world. When we go down to how we evolve, why we are born and then die, and never in the opposite order, why we remember what happened yesterday and we don't remember what is going to happen tomorrow, all of these manifestations of the difference between the past and the future are all coming from the same source. That source is the low entropy of the Big Bang.
This is something that was touched on way back in the 19th century when the giants of thermodynamics like Boltzmann and Maxwell were trying to figure out how entropy works.... Boltzmann... was stuck on this question of why was the entropy low to begin with.... Boltzmann invented the idea of a multiverse, the anthropic principle where things were different in some regions of the universe than in others and that we lived in an unrepresentative part of it. But he never really quite settled on what he thought was the right answer.... We know very well how to explain that I remember yesterday and not tomorrow, but only if we assume that we start the universe in a low entropy state.
I like to say that observational cosmology is the cheapest possible science to go into. Every time you put milk into your coffee and watch it mix and realize that you can't unmix that milk from your coffee, you are learning something profound about the Big Bang, about conditions in the very, very early universe. This is just a giant clue that the real universe has given to us to how the fundamental laws of physics work. We don't yet know how to put that clue to work. We don't know the answer to the who done it, who is the guilty party, why the universe is like that. But taking this question seriously is a huge step forward in trying to understand how the universe that we see around us directly fits into a much bigger picture.