Relativity: Space, Time, and Gravity

Why moving clocks run slow and gravity is curved spacetime, in plain language — special and general relativity, with GPS as the everyday proof.

1. Special Relativity: One Rule, Strange Consequences The speed of light is the same for every observer — and that one unbending fact forces moving clocks to run slow, lengths to shrink, and mass to be frozen energy.
2. General Relativity: Gravity Is Curved Spacetime Standing on Earth feels identical to accelerating in a rocket — and from that one observation gravity turns out to be the curving of spacetime by mass, not a force pulling at all.
3. The Evidence and the Everyday GPS would drift kilometers a day without relativity, starlight bends around the Sun, Mercury's orbit drifts on schedule, and LIGO heard spacetime ring — the proof that relativity is real, not theory.