Albert Einstein's theory of special relativity (1905) and general relativity (1915) overturned Newton's absolute space and time. Special relativity showed that the speed of light is the same for all observers, leading to time dilation, length contraction, and the equivalence of mass and energy (E=mc²). General relativity went further, revealing that gravity is not a force but the curvature of spacetime caused by mass and energy.
These theories are not abstract curiosities — GPS satellites must correct for both special relativistic time dilation (clocks tick slower when moving fast) and general relativistic effects (clocks tick faster in weaker gravity) to maintain accuracy. Without relativistic corrections, GPS would drift by ~10 km per day.
These simulations let you experience relativistic effects: watch clocks slow down at high speeds, see objects contract in the direction of motion, resolve the twin paradox, and convert mass to energy using Einstein's most famous equation.