Physicists’ best theory of matter is quantum mechanics, which describes the discrete (quantized) behavior of microscopic particles via wave equations. Their best theory of gravity is general relativity, which describes the continuous (classical) motion of massive bodies via space-time curvature. These two highly successful theories appear fundamentally at odds over the nature of space-time: quantum wave equations are defined on a fixed space-time, but general relativity says that space-time is dynamic—curving in response to the distribution of matter. Most attempts to solve this tension have focused on quantizing gravity, with the two leading proposals being string theory and loop quantum gravity. But new theoretical work by Jonathan Oppenheim at University College London proposes an alternative: leave gravity as a classical theory and couple it to quantum theory through a probabilistic mechanism [1]. Such a hybrid strategy was traditionally considered a nonstarter, as it was thought to lead to inconsistencies [2]. Oppenheim avoids these pitfalls, but at the cost of having to insert probability—a “roll of dice”—into the evolution of space-time. Future experiments could test the viability of this approach by probing whether gravity is quantum.
To read more, click here.