Definition
Quantum theory (also called quantum mechanics) is a fundamental theory in physics that describes the physical properties of nature at the scale of atoms and subatomic particles. ⚛️ It's weird! Energy, momentum, angular momentum, and other quantities are restricted to discrete values (quantized). Objects have characteristics of both particles and waves (wave-particle duality). Physical quantities cannot be predicted with complete certainty. Instead, probabilities are calculated. Think of flipping a coin; quantum theory helps predict if you'll get heads or tails. It's the basis for much of modern technology.