Xingyang Yu

The boundary sets the rules Quantum gravity is like a theater where spacetime is the stage and fields are the actors. When the stage has an edge, you need to know exactly what happens at the boundary; otherwise, the play falls apart. In 2018, Edward Witten proposed an elegant recipe for such a case.

The holographic principle is often compared to a hologram: all the information about a volume is encoded on a flat surface. In physics, this means that three-dimensional spacetime with gravity could be equivalent to a two-dimensional theory without gravity — a so-called conformal field theory (CFT).