The basis for most ideas around potential time travel lies in Albert Einstein’s special and general theories of relativity, which he published in 1905 and 1915, respectively. Travel into the Future thanks to Rapid MovementEinstein’s special theory of relativity makes time travel possible—but only into the future. Journeys into the PastTechnically, the equations of general relativity also allow for backward time travel through the existence of so-called closed timelike curves. Why did more than 20 years pass between the development of general relativity and this insight? The Einstein field equations that underly general relativity are differential equations.