Special Relativity
When you move close to the speed of light, strange things happen. Time slows down (time dilation). Mass increases. Length contracts. Einstein's famous equation E=mc² shows mass and energy are the same thing — and a tiny bit of mass contains enormous energy.
Quantum Mechanics
At tiny scales, particles behave like waves and waves behave like particles. You can never know both position and momentum exactly — Heisenberg's uncertainty principle. Schrödinger's cat is both alive and dead until observed.
What Einstein Got Wrong (Sort Of)
Einstein spent 30 years trying to unify gravity with quantum mechanics but never succeeded. Modern physics's biggest unsolved problem is still finding a 'theory of everything' that combines general relativity with quantum mechanics.
Why It Matters
Modern physics gave us semiconductors (all computers), lasers, LEDs, GPS (relativity corrections are necessary!), MRI machines, and nuclear power. The weird physics of the very small and very fast became the foundation of the modern world.