The Theory of Everything

The Theory of Everything (ToE) is the ultimate goal of physics — a single theoretical framework that fully explains and links together all physical aspects of the universe. It would reconcile General Relativity (which describes gravity and the large-scale universe) with Quantum Mechanics (which describes the subatomic world) — two theories that are individually spectacularly successful but fundamentally incompatible. The leading candidate is String Theory, which proposes that all fundamental particles are actually tiny one-dimensional "strings" vibrating at different frequencies. String theory requires extra dimensions beyond our familiar four (three of space and one of time) — possibly 10 or 11 dimensions in total. Alternatives include Loop Quantum Gravity, Causal Dynamical Triangulation, and others. None has yet made testable predictions that distinguish it from alternatives. Finding a ToE would represent the end of a centuries-long quest beginning with Newton's unification of terrestrial and celestial gravity, continuing through Maxwell's unification of electricity and magnetism, and Einstein's unification of space and time.