Kaluza-Klein theory

Kaluza-Klein theory is a framework in physics that attempts to unify gravity and electromagnetism by positing extra spatial dimensions beyond the familiar three.

Originally proposed in the 1920s, it suggests these additional dimensions are compactified—curled up so small they're undetectable.

The theory laid groundwork for later multidimensional approaches like string theory: Kaluza-Klein theory introduced the idea that hidden dimensions could explain fundamental forces.