This result holds for any pair of incompatible observables, since the commutator of the corresponding operators is non-zero. It was introduced in a paper on the interpretation of matrix mechanics which included a thought experiment with a gamma-ray microscope. Part of the Copenhagen interpretation of quantum mechanics, it weakens causality since perfect information is impossible. For 10 points—name this principle stating 
This result holds for any pair of incompatible observables, since the commutator of the corresponding operators is non-zero. It was introduced in a paper on the interpretation of matrix mechanics which included a thought experiment with a gamma-ray microscope. Part of the Copenhagen interpretation of quantum mechanics, it weakens causality since perfect information is impossible. For 10 points—name this principle stating the a subatomic particle's position and momentum cannot be simultaneously and precisely known.
This result holds for any pair of incompatible observables, since the commutator of the corresponding operators is non-zero.
{Heisenberg uncertainty} [or {Heisenberg indeterminacy} etc.]