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uncertainty principle

The uncertainty principle is the concept that precise, simultaneous measurement of some complementary variables -- such as the position and momentum of a subatomic particle -- is impossible. Contrary to the principles of classical physics, the simultaneous measurement of such variables is inescapably flawed; the more precisely one is measured, the more flawed the measurement of the other will be.

The uncertainty principle, also known as the Heisenberg indeterminancy principle, is an essential component of quantum theory . Werner Heisenberg discovered the uncertainty principle and explained it in a 1927 paper:

"The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa."

(translated from Über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik )

Pairs of observable attribute s of a single elementary particle that have what is called an uncertainty relationship are known as conjugate variables . Elementary particles are those without any further substructure, including leptons, quark s and gauge bosons.

The uncertainty principle is represented mathematically by a set of theorems of functional analysis, deriving from the mathematical definition of operator s in quantum mechanics . In practical terms, the concept means that no analysis of a scientific experiment is accurate without acknowledging the nature of the probability distribution (or error) of the measurement itself.

The creation of quantum theory , quantum mechanics and Einstein's theory of relativity formed the basis for modern physics. The principles of quantum physics are still being applied in an increasing number of areas, including quantum optics , quantum chemistry , quantum computing and quantum cryptography .

The uncertainty principle is what prompted Albert Einstein's famous comment, "God does not play dice." Frustrated by incompatible aspects of quantum theory and his theory of relativity, Einstein devoted many years to the search for a unified field theory that would reconcile those issues. The current quest for a unified field theory (sometimes called the holy grail of physicists) is largely focused on superstring theory and, in particular, on an adaptation known as M-theory .

This was last updated in August 2006

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