Heisenberg's uncertainty principle 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. [2] The formal inequality relating the standard deviation of position σ x and the standard deviation of momentum σ p was derived by Earle Hesse Kennard [3] later that year and by Hermann Weyl [4] in 1928: {\displaystyle \sigma _{x}\sigma _{p}\geq {\frac {\hbar }{2}}~~} Ordinary experience provides no clue of this p