Theory of Relativity: The Revolution of Time and Space

In 1905, a 26-year-old patent clerk named Einstein published four revolutionary papers. The key question had haunted him since age 16: what would it look like to ride alongside a light wave? Newtonian physics says light should have a relative speed, but Maxwell's equations show light speed is always constant. The answer to this contradiction was astonishing: it's not speed that changes, but time and space. This is special relativity. And from this theory, E=mc² was derived.

I have no special talents. I am only passionately curious — Albert Einstein

Two axioms of special relativity: ① physics laws are identical in all inertial frames; ② light speed is always c. From these come time dilation (faster = slower clock) and length contraction (faster = shorter). E=mc²: mass and energy are equivalent. Since c² is enormous, even tiny mass equals vast energy. General relativity (1915): gravity is not a force but the curvature of spacetime caused by mass.