Heisenberg uncertainty principle

The Heisenberg uncertainty principle is a fundamental concept in quantum mechanics stating that certain pairs of physical properties—most famously position and momentum—cannot both be precisely measured simultaneously.

The more accurately you know a particle's position, the less accurately you can know its velocity, and vice versa.

This isn't a limitation of measuring instruments but a basic feature of reality at the quantum scale.

The principle is often invoked loosely to suggest that observation changes what's observed: Like the uncertainty principle, polling might affect how people actually vote.