Uncertainty principle
Uncertainty principle
A principle of quantum mechanics (q.v.), according to which complete quantitative measurement of certain states and processes in terms of the usual space-time coordinates is impossible. Macroscopically negligible, the effect becomes of importance on the electronic scale. In particular, if simultaneous measurements of the position and the momentum of an electron are pressed beyond a certain degree of accuracy, it becomes impossible to increase the accuracy of either measurement except at the expense of a decrease in the accuracy of the other more exactly, if a is the uncertaintv of the measurement of one of the coordinates of position of the electron and b is the uncertainty of the measurement of the corresponding component of momentum, the product ab (on principle) cannot be less than a certain constant h (namely Planck’s constant, q.v.). On the basis that quantities in principle unobservable are not to be considered physically real, it is therefore held by quantum theorists that simultaneous ascription of an exact position and an exact momentum to an electron is memingless. This has been thought to have a bearing on, or to limit or modify the principle of determinism in physics. — A.C.
C. G. Darwin, The uncertainty principle, Science, vol. 73 (1931), pp. 653-660.