Exactly 200 years ago, a French engineer introduced an idea that would quantify the universe’s inexorable slide into decay. But entropy, as it’s currently understood, is less a fact about the world ...

The following is an extract from our Lost in Space-Time newsletter. Each month, we hand over the keyboard to a physicist or two to tell you about fascinating ideas from their corner of the universe.

Imagine you’re standing in front of a closed door. Behind it is a teenager’s bedroom, and your task is to rate how messy it is on a scale of 1 to 10. But here’s the twist: you can’t open the door – ...