String Theory

String theory proposes that all fundamental particles are not point-like but are instead tiny one-dimensional vibrating strings, with different vibrational modes producing different particles. It potentially unifies quantum mechanics and general relativity — the two great incompatible theories of 20th-century physics — and requires 10 or 11 dimensions. String theory is extraordinarily mathematically beautiful — it has inspired thousands of papers and attracted the world's best physicists. However, it has yet to make a testable experimental prediction — making it arguably not falsifiable and thus not scientific by Karl Popper's definition. Critics (including Peter Woit, Lee Smolin) argue it is 'not even wrong.' Its proponents argue that its mathematical coherence makes it the leading candidate for physics' ultimate theory.