Werner Heisenberg

Werner Heisenberg (1901 to 1976) was the German physicist who in 1925 produced matrix mechanics, the first complete and self-consistent formulation of quantum mechanics, and who in 1927 stated the uncertainty principle. His work replaced the earlier patchwork of quantum rules with a systematic theory and set fundamental limits on what can be simultaneously known about a particle. He won the Nobel Prize in Physics for 1932.

#Matrix mechanics

Working on the North Sea island of Helgoland in 1925, Heisenberg reformulated atomic physics using only observable quantities such as the frequencies and intensities of spectral lines, discarding unobservable electron orbits. His scheme, developed further with Max Born and Pascual Jordan, expressed physical quantities as arrays that multiply in a non-commuting way, which Born recognized as matrix algebra. This matrix mechanics was the first complete quantum theory, and the Nobel committee later credited him "for the creation of quantum mechanics" (Nobel Prize facts). It was soon shown to be mathematically equivalent to the wave formulation that Erwin Schrodinger published in 1926.

#The uncertainty principle

In 1927 Heisenberg showed that certain pairs of properties, such as a particle's position and momentum, cannot both be measured to arbitrary precision at the same time: the more sharply one is fixed, the less sharply the other is defined (SEP: uncertainty principle). The uncertainty principle is not a limit of instruments but a structural feature of quantum theory, tied to the non-commuting quantities of matrix mechanics. Heisenberg first argued the point through a thought experiment about locating an electron with a microscope, and the relation was soon given a precise mathematical form. It became a pillar of the Copenhagen interpretation that Heisenberg developed alongside Niels Bohr, and it framed the questions about observation and reality debated at the 1927 Solvay Conference in Brussels.

#Significance

Heisenberg's matrix mechanics and Schrodinger's wave mechanics were the two independent routes to modern quantum mechanics, and their equivalence, shown by Schrodinger and by Paul Dirac's more general framework, unified the field. The uncertainty principle reshaped ideas about determinism and measurement and remains central to the measurement problem and to physics as a whole. His 1925 breakthrough is a landmark in the history of quantum mechanics, and Feynman diagrams, wave functions, and matrices are today understood as different expressions of the single theory he helped create.

#History

Heisenberg was born in Wurzburg in 1901 and studied under Arnold Sommerfeld in Munich and Max Born in Gottingen, with formative periods alongside Bohr in Copenhagen (Nobel biographical). During the Second World War he led part of the German nuclear research program, a role that has remained the subject of extensive historical debate. After the war he helped rebuild German science and directed the Max Planck Institute for Physics. He died in 1976.