I recently just heard of this thought experiment where two rooms/resoviors whatever you want to call them are adjoined by a door that a little demon controls. Both rooms have the same temperature, The demon then opens this door when particles with higher kinetic energy are nearby to let them into one side, while letting particles with lower kinetic energy into the other side. Eventually one room is hotter and the other is colder. I read that this is impossible. Why is this impossible?