For decades, physicists have struggled to develop a quantum theory of gravity. But what if gravity — and space-time — are fundamentally classical?
Most physicists expect that when we zoom in on the fabric of reality, the unintuitive weirdness of quantum mechanics persists down to the very smallest scales. But in those settings, quantum mechanics collides with classical gravity in a resolutely incompatible way.
So for almost a century, theorists have tried to create a unified theory by quantizing gravity, or sculpting it according to the rules of quantum mechanics. They still haven’t succeeded.