The Short Version
This claim is false. The "Mozart effect" originated from a 1993 study on college students — not babies — and produced only a brief, temporary boost in spatial reasoning, not general cognitive intelligence. Multiple meta-analyses and peer-reviewed reviews have found no persuasive evidence that passively listening to Mozart increases cognitive intelligence in infants. The original researcher herself stressed the effect does not extend to general intelligence. The widespread belief persists as a popular myth unsupported by scientific evidence.