Definition · Plain-language
Quantum physics
Quantum physics is the branch of physics that describes how matter and energy behave at the smallest scales — atoms, electrons and light.
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Physics of the very small
Quantum physics is the theory that governs the behaviour of matter and energy on the scale of atoms and the particles inside them. At everyday sizes the familiar physics of Newton works perfectly, but in the atomic world it breaks down and a different set of rules takes over. The name comes from the discovery that energy is not continuous but comes in tiny, indivisible amounts called quanta. This realisation, early in the twentieth century, launched one of the most successful and accurately tested theories in all of science.
Waves, particles and probability
Two ideas sit at the heart of quantum physics. The first is wave–particle duality: things we picture as particles, such as electrons, also behave like waves, and light can act as both a wave and a stream of particles called photons. The second is that quantum events are inherently probabilistic. Rather than predicting exactly where a particle will be, the theory gives the probability of each possible outcome, captured by a mathematical object called the wavefunction. Heisenberg’s uncertainty principle adds that certain pairs of properties, such as position and momentum, cannot both be known precisely at once.
Why it matters in daily life
Quantum physics is not just abstract theory; it explains the everyday world and powers modern technology. The way atoms bond into molecules, and therefore all of chemistry, follows quantum rules. Transistors and microchips, lasers, LED lights, medical scanners and solar cells all depend on quantum behaviour. Emerging fields such as quantum computing and quantum cryptography aim to harness distinctively quantum effects like superposition and entanglement directly, promising new kinds of computation and secure communication.
Key facts
At a glance
- Definition: physics of matter and energy at atomic and subatomic scales
- Also called: quantum mechanics
- Quanta: energy comes in discrete packets, not a continuous flow
- Duality: particles such as electrons also behave as waves
- Probabilistic: outcomes are predicted as probabilities, not certainties
- Underpins: chemistry, transistors, lasers, LEDs and solar cells
Common misconceptions
What people often get wrong
Often heard: Quantum physics is just unproven speculation.
Actually: Quantum mechanics is among the most precisely tested theories in science, confirmed to extraordinary accuracy, and it underlies technology you use every day, from microchips to LED lights.
Often heard: Quantum effects can be seen with everyday objects.
Actually: Quantum behaviour normally shows up only at the scale of atoms and particles. Large objects follow classical physics because quantum effects average out and become unobservable at human scales.
Often heard: Entanglement lets information travel faster than light.
Actually: Entanglement creates correlations between distant particles, but it cannot be used to send a usable signal faster than light, so it does not break the cosmic speed limit set by relativity.
Going deeper
