How Did the Universe Start? | Cosmic VarianceWhere entropy increases, there goes time. Or so it goes.
... The baby-universe idea at least has the chance to give rise to a spontaneous violation of time-reversal symmetry and explain the arrow of time. If we start with empty space an evolve it forward, baby universes can (hypothetically) be born; but the same is true if we run it backwards. The increase of entropy doesn’t arise from a fine-tuning at one end of the universe’s history, it’s a natural consequence of the ability of the universe to always increase its entropy. We’re a long way from completely understanding such a picture; ultimately we’ll have to be talking about a Hilbert space of wavefunctions that involve an infinite number of disconnected components of spacetime, which has always been a tricky problem. But the increase of entropy is a fact of life, right here in front of our noses, that is telling us something deep about the universe on the very largest scales.
Update 4/28/07: Infinitely expanding universes birthing within infinitely expanding universes. Requirements for human observation to collapse probability waves. All interpretations of self-consistent mathematics, but way beyond bizarre. Which leads to the scary thought. Could he be right? Brrrr.