The Challenge of Quantum Gravity

A central expectation is that gravity itself should ultimately follow the rules of quantum mechanics. That possibility quickly becomes difficult to visualize.

Quantum mechanics allows an object to be delocalized across multiple locations at the same time, an effect that has been repeatedly demonstrated with atoms and even small pieces of metal. Einstein’s theory, meanwhile, treats gravity as a property of space and time itself — it can bend, flatten, and support waves that travel through it, as gravitational wave detectors have confirmed.