# Introduction to Quantum Physics;Heisenberg's uncertainty principle

In quantum mechanics, the uncertainty principle (also known as Heisenberg's uncertainty principle) is any of a variety of mathematical inequalities[1] asserting a fundamental limit to the precision with which certain pairs of physical properties of a particle, known as complementary variables, such as position x and momentum p, can be known.

Introduced first in 1927, by the German physicist Werner Heisenberg, it states that the more precisely the position of some particle is determined, the less precisely its momentum can be known, and vice versa.The formal inequality relating the standard deviation of position Ïƒx and the standard deviation of momentum Ïƒp was derived by Earle Hesse Kennard[3] later that year and by Hermann Weyl[4] in 1928:

where Ä§ is the reduced Planck constant, h/(2Ï€).

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