Heisenberg Uncertainty Principle
A similar relation from Fourier analysis for time and frequency: ?t * ?? = 1/2 leads to another part of the Uncertainty Principle (using E = hf): ?t * ?E > ?/2 .
There is a third part: ???* ?L > ?/2 (where L is the angular momentum value).
All of this is a direct result of the wave/particle duality of light and matter.