Heisenberg Uncertainty Principle
This principle states that it is not possible to know two complementary parameters precisely (such as position and momentum, energy and time, or angular momentum and angular displacement), the more you know about one, the less you know about the other.
Werner Heisenberg stated that the product of uncertainties in location and momentum measurements can never be smaller than h/4, where h is Planck's constant.
This is central to quantum mechanics. First explained by Werner Heisenberg in 1927.