Theory of Relativity
Albert Einstein's revolutionary framework for understanding space, time, and gravity - published in 1905 and 1915.
⚡ Special Relativity (1905)
Two postulates: (1) the laws of physics are identical for all inertial observers, and (2) the speed of light in a vacuum is constant (~3×10⁸ m/s) for all observers regardless of motion.
⏱️ Time Dilation
Moving clocks run slower relative to stationary ones. t' = t/√(1−v²/c²). GPS satellites travel fast enough that their clocks slow by 7 microseconds/day - software corrects for this constantly.
📏 Length Contraction
Objects in motion appear shorter along the direction of motion to a stationary observer. L = L₀√(1−v²/c²). At 87% the speed of light, an object appears half its rest length.
⚛️ Mass-Energy Equivalence
The most famous equation in science: E = mc². A tiny amount of mass corresponds to an enormous amount of energy. This is the exact principle behind nuclear fission and fusion energy release.
🌌 General Relativity (1915)
Gravity is not a force but the curvature of spacetime caused by mass and energy. Massive objects warp spacetime, causing other objects (including light) to follow curved paths through it.
🕳️ Black Holes
Predicted by general relativity: regions where spacetime curvature is so extreme that not even light can escape. The event horizon is the point of no return. The first image was captured in 2019 by the Event Horizon Telescope.
🌊 Gravitational Waves
Ripples in spacetime caused by accelerating massive objects (e.g., merging black holes). Predicted by Einstein in 1916, first directly detected by LIGO in 2015 - 100 years later.
🔴 Gravitational Redshift
Light climbing out of a gravitational field loses energy and shifts to longer (redder) wavelengths. Light from the Sun is slightly redshifted. This also means clocks run slower in stronger gravitational fields.