In quantum mechanics, a system can be in multiple states at once. That is superposition. An electron can be in two places at the same time, or spinning in two directions at once, until it is measured. When measured, it collapses into one state. Superposition is one of the strangest and most important features of quantum mechanics. It is the basis of quantum computing, where qubits can be in superposition of 0 and 1, allowing parallel computation.

Superposition is not just a theoretical idea. It has been demonstrated in countless experiments. The double-slit experiment shows that a single electron can pass through both slits at once and interfere with itself. Quantum computers use superposition to perform calculations that classical computers cannot. Schrödinger's cat is a thought experiment that illustrates the strangeness of superposition. A cat in a box is both dead and alive until the box is opened. The thought experiment was meant to show the absurdity of superposition when applied to everyday objects. But superposition is real, at least at the quantum scale. Decoherence explains why we do not see it in everyday life. Any interaction with the environment collapses the superposition.

Superposition facts

• Definition. A system in multiple states at once.
• Measurement. Collapses into one state.
• Double-slit. Demonstrates superposition of a single particle.
• Quantum computing. Qubits in superposition enable parallel computation.
• Decoherence. Environment collapses superposition.

Superposition is not the same as uncertainty. Uncertainty is about what we can know. Superposition is about what is real.