Entropy Is Not Disorder: A Physicist’s Perspective

Entropy is often treated as synonymous to chaos and disorder. But what is it really? In this article, we explore how entropy is more about ignorances.

From the “invisible force” to the “harbinger of chaos,” you may have heard quite a few sensational phrases describing entropy.

But what is it really? The equations—frequently misunderstood—tell a more humbling story.

In many cases, entropy doesn’t capture anything particularly deep about a physical system. In fact, it says more about our understanding of the system than the system itself.

The main punchline is:

entropy measures our ignorance of a system

Let’s dissect how and why this is the proper way to understand entropy.

Understanding Entropy’s Definition

Starting from the beginning, the classical definition of entropy in physics, S, is given by the equation

where N is the number of states for a given system. The definition seems deceptively simple. However, the devil lies in the details: What do we mean by “the number of states?” How do we count this…