Why Does Time Have a Future?: The Physical Origins of the Arrow of Time

It seems paradoxical that the laws of physics are invariant under a reversal of time, whereas everyday experience clearly indicates a direction of time, distinguishing the past from the future. The course of events is generally irreversible. Nevertheless, this observation can be reduced to the fundamental laws of physics: reversibility is a feature of the microscopic, atomistic world, whereas irreversibility is an emergent feature of the macroscopic world due to our coarsegrained knowledge about it, combined with very special, highly unlikely initial conditions of the universe as they existed at the time of the Big Bang. The explanation of the arrow of time is a case study of a completely reductionist explanation of a phenomenon in nature, which, however, sees the emergence of concepts that are not present in the fundamental description of the world.