Special Relativity
Nothing travels faster than light. In 1905, Einstein revealed that the speed of light is the ultimate cosmic speed limit -- constant for all observers, regardless of their motion. This single postulate shattered centuries of Newtonian assumptions and rewrote the rules of the universe.
E = mc2
Mass-energy equivalence
Time Dilation
Time is not absolute. A clock moving at high velocity ticks slower than a stationary one. Astronauts on the International Space Station age microseconds less than people on Earth. At speeds approaching light, seconds stretch into hours, and the boundary between past and future blurs.
Δt' = Δt / √(1 - v²/c²)
Lorentz time dilation
General Relativity
Gravity is not a force -- it is the curvature of spacetime itself. Massive objects like stars and planets warp the fabric of space around them, and other objects follow these curves. The Earth orbits the Sun not because it is pulled, but because it follows the straightest possible path through curved spacetime.
Gμν + Λgμν = (8πG/c4)Tμν
Einstein field equations
Gravitational Lensing
Light bends around massive objects. When a distant galaxy's light passes near a massive cluster, the cluster's gravity bends the light like a cosmic magnifying glass. This gravitational lensing reveals hidden galaxies, amplifies faint signals, and provides direct evidence that spacetime itself is curved.
The Fabric of Spacetime
Space and time are woven together into a single four-dimensional continuum. Every event in the universe has coordinates in both space and time. Mass and energy tell spacetime how to curve, and curved spacetime tells matter how to move. This elegant interplay is the deepest truth of general relativity.
Gravitational Waves
When massive objects accelerate -- when black holes merge or neutron stars collide -- they send ripples through the fabric of spacetime. These gravitational waves, predicted by Einstein in 1916 and first detected by LIGO in 2015, stretch and compress space itself as they pass through the universe.