Can the Arrow of Time be understood from Quantum Cosmology?

TL;DR

This paper explores whether the arrow of time can be explained through quantum cosmology by analyzing entropy, boundary conditions, and decoherence in the universe's wave function, linking time's direction to universe expansion and entanglement.

Contribution

It proposes that quantum geometrodynamics with a low initial entropy boundary condition can naturally explain the emergence of the arrow of time.

Findings

Arrow of time correlates with universe size.

Decoherence due to entanglement explains time's direction.

Low initial entropy boundary condition is plausible in quantum cosmology.

Abstract

I address the question whether the origin of the observed arrow of time can be derived from quantum cosmology. After a general discussion of entropy in cosmology and some numerical estimates, I give a brief introduction into quantum geometrodynamics and argue that this may provide a sufficient framework for studying this question. I then show that a natural boundary condition of low initial entropy can be imposed on the universal wave function. The arrow of time is then correlated with the size of the Universe and emerges from an increasing amount of decoherence due to entanglement with unobserved degrees of freedom. Remarks are also made concerning the arrow of time in multiverse pictures and scenarios motivated by dark energy.