Who proposed the uncertainty principle?

Werner Heisenberg proposed the uncertainty principle. He introduced the idea in 1927, arguing that quantum mechanics places a fundamental limit on how precisely certain pairs of properties, such as a particle's position and momentum, can be known together.

The principle is expressed through an inequality involving the standard deviations of position and momentum: their product cannot be smaller than a quantity related to the reduced Planck constant. This is not merely a limitation of imperfect instruments. It follows from the mathematical structure of quantum mechanics and the wave-like nature of matter.

Heisenberg's original discussion emphasized the disturbance caused by measurement, but modern treatments distinguish that idea from intrinsic statistical uncertainty. The formal position-momentum relation was derived by Earle Hesse Kennard in 1927 and later generalized by Hermann Weyl.

A common misconception is that the principle says everything in quantum physics is vague or unknowable. It applies specifically to pairs of non-commuting observables. For example, a particle can have a precisely defined energy in a stationary state even while other quantities remain uncertain.