Source of the observed thermodynamic arrow

TL;DR

This paper explains the thermodynamic arrow of time as a consequence of cosmic expansion and a shift from short-range to long-range forces, eliminating the need for special entropy-lowering mechanisms.

Contribution

It proposes a cosmological explanation for the thermodynamic arrow based on force dominance transition during universe expansion.

Findings

At a specific epoch, high-entropy states become extremely unlikely due to force transition.

The shift from short-range to long-range forces occurred around the time of decoupling.

No special entropy-lowering mechanisms are needed to explain the arrow of time.

Abstract

The puzzle of the thermodynamic arrow of time reduces to the question of how the universe could have had lower entropy in the past. I show that no special entropy lowering mechanism (or fluctuation) is necessary. As a consequence of expansion, at a particular epoch in the history of the universe a state that was near maximum entropy under the dominant short range forces becomes extremely unlikely, due to a switchover to newly dominant long range forces. This happened at about the time of decoupling, prior to which I make no statement about arrows. The role of cosmology in thermodynamics was first suggested by T. Gold.