In 1905 a 26-year-old patent clerk took two innocent-looking assumptions — the laws of physics look the same to everyone moving steadily, and light has the same speed for everyone — and followed them without flinching. Out came a universe where moving clocks run slow, moving rulers shrink, and two people can honestly disagree about whether two events happened at the same time.
Special relativity is the physics of space and time woven into a single fabric,
spacetime. This branch builds it from the postulates: time dilation, length contraction,
the Lorentz transformation, the relativity of simultaneity, and the most famous equation in
science,