Physics
Relativity
A theory built almost entirely from thought experiments in a patent office — later confirmed true down to fractions of a second.
Quantum Mechanics
The rules of the universe change once you zoom in far enough — and even the physicists who discovered this found it deeply unsettling.
Thermodynamics
Four simple laws that explain why your coffee always goes cold, and never once has it spontaneously reheated itself back to piping hot.