Uncertainty Principle

Principle central to quantum mechanics, which states that two complementary parameters (such as position and momentum, energy and time, or angular momentum and angular displacement) cannot both be known to infinite accuracy. The more you know about one, the less you know about the other. It can be illustrated in a fairly clear way as it relates to position vs. momentum. For example, to see an electron, one has to fire photons at it. The photons bounce off and return, allowing one to see the electron. Low-energy photons will not impart much momentum to the electron (higher certainty in momentum), but yield a very fuzzy picture (a higher uncertainty in position). High-energy photons (x-rays or γ-rays) provide a very clear picture of the electron’s location (high certainty in position), but impart a great deal of momentum to the electron (higher uncertainty in momentum). In a more generalized sense, the uncertainty principle tells us that the act of observing changes the observed in fundamental way.