The General Theory of Relativity by Albert Einstein (1915)

The General Theory of Relativity, developed by Albert Einstein and published in 1915, fundamentally changed our understanding of space, time, and gravity. Instead of viewing gravity as a simple force between objects, Einstein showed that massive objects curve spacetime itself, and that motion follows this curvature. This theory explained previously mysterious phenomena, such as the precise orbit of Mercury, and predicted entirely new ones, including gravitational waves and black holes, all of which were later confirmed. Though mathematically complex, general relativity reshaped modern physics and remains essential for understanding the universe on its largest scales, from GPS satellites to the evolution of galaxies.