Why general relativity is known as a background independent theory

Space-time isn’t expanding into anything because general relativity is what we call a background independent theory. Chanda Prescod-Weinstein sets out to explain what this means

By Chanda Prescod-Weinstein

LAST month, I answered a reader question about space-time expansion. They wanted to know what space-time is expanding into, given that we scientists tend to analogise with a balloon that is being blown up. As I wrote, this analogy has a flaw because when we blow up a balloon, it is expanding with a room in the background.

In reality, space-time has no background because general relativity is what we call a background independent theory. Which of course invites the question: “What’s that?” The problem is this column has to fit on a single page. I tried to …