The Heisenberg Uncertainty Principle

Uncertainty is one of the best known implications of the quantum revolution. In 1927 Heisenberg argued that key physical quantities (e.g. position and momentum) are paired up in quantum theory. As a result, they cannot be measured simultaneously to any desired degree of accuracy. Attempts to increase the precision of one measurement result in less precise measures of the other member of the pair.

Take an electron, for example. We might try to determine its position by using electromagnetic radiation. Because electrons are so small, radiation of very short wavelength would be necessary to locate it accurately. However, shorter wavelengths correspond to higher energies. The higher the energy of radiation use, the more the momentum of the electron is altered. Thus any attempt to determine the location accurately will change the velocity of the electron. Conversely, techniques for accurately measuring the velocity of the electron will leave us in ignorance about its precise location.

Further discussion of the Uncertainty Principle can be found in John Polkinghorne’s largely non-technical book The Quantum World.

The Significance of Uncertainty:

The conservative interpretation was that uncertainty was a limitation imposed by our measuring techniques.

However, Heisenberg himself took a more radical view - that this limitation is a property of nature rather than an artifact of experimentation. This radical interpretation of uncertainty implies that quantum mechanics is inherently statistical - it deals with probabilities rather than well-defined classical trajectories. Such a view is clearly inimical to classical determinism. See Shaking the Foundations: the implications of quantum theory.

Email link | Feedback | Contributed by: Dr. Christopher Southgate
Source: God, Humanity and the Cosmos  (T&T Clark, 1999)