Heisenberg Uncertainty Principle
The principle that the position and momentum of a particle cannot both be known to arbitrary precision at the same time.
Formula / equation
Δx · Δp ≥ h / 4π
Unit
J·s
In depth
The limit is intrinsic to the wave nature of matter, not a defect of measurement. It rules out Bohr's precisely defined orbits and forces the probabilistic orbital description. Because the bound is set by Planck's constant, the effect is negligible for everyday objects but decisive for electrons.
Examples in the real world
Fixing an electron's position to 0.1 nm leaves its velocity uncertain by more than 10⁶ m/s — larger than the velocity itself.