Why an Old Theory of Everything Is Gaining New Life

Twenty-five particles and four forces. That description—the Standard Model of particle physics—constitutes physicists’ best current explanation for everything. It’s neat and it’s simple, but no one is entirely happy with it. What irritates physicists most is that one of the forces—gravity—sticks out like a sore thumb on a four-fingered hand. Gravity is different. Quanta Magazine …