The speed of light is constant for all observers. Time dilates, lengths contract, and simultaneity becomes relative. The universe's speed limit reshapes our understanding of cause and effect.
E = mc2Mass curves spacetime. Gravity is not a force but geometry -- objects follow the straightest possible paths through curved space. The larger the mass, the deeper the curve.
Guv = 8πTuvFour dimensions woven together -- three of space, one of time. Events are points. Worldlines are paths. The interval between events is invariant for all observers.
ds2 = -c2dt2 + dx2Two identical clocks start synchronized. One travels at 0.9c and returns. The traveling clock reads less time. This is not an illusion -- the geometry of spacetime makes it real.
c = 299,792,458 m/sSpecial Relativity
General Relativity
Still Discovering