The Second Law and Cosmology

TL;DR

This paper discusses how cosmological examples demonstrate that the second law of thermodynamics remains relevant, addressing puzzles about the universe's low initial entropy and the vastness of reality beyond observable limits.

Contribution

It highlights the ongoing relevance of the second law in cosmology and offers insights into the universe's entropy and size beyond observable horizons.

Findings

The universe's low initial entropy is linked to inflationary expansion.

The observable universe is a small, uniform patch within a much larger, more complex reality.

The second law continues to inspire research into fundamental cosmological questions.

Abstract

I use cosmology examples to illustrate that the second law of thermodynamics is not old and tired, but alive and kicking, continuing to stimulate interesting research on really big puzzles. The question "Why is the entropy so low?" (despite the second law) suggests that our observable universe is merely a small and rather uniform patch in a vastly larger space stretched out by cosmological inflation. The question "Why is the entropy so high" (compared to the complexity required to describe many candidate "theories of everything") independently suggests that physical reality is much larger than the part we can observe.