Werner Heisenberg was one of the leading German physicists of the century and was one of the founders of quantum mechanics. In 1925, he introduced a formulation of quantum mechanics, known as matrix mechanics, which correctly predicted the observed energy levels of the hydrogen atom. (Soon afterwards, Erwin Schrödinger put forward his simpler wave mechanics, which was eventually shown to be mathematically equivalent to matrix mechanics.) Heisenberg had strong philosophical interests and was influential in the formulation of the Copenhagen interpretation of quantum mechanics. However he is perhaps most famous for his uncertainty principle, which he developed in 1927, following discussions with Albert Einstein. According to the principle, if an observer measures the value of the position of a quantum, the uncertainty in this value directly affects the simultaneous uncertainty in the momentum of the quantum (the same is true for certain other pairs of variables, such as energy and time). Also, Heisenberg used the Pauli exclusion principle to show that ferromagnetism is caused by electrostatic interactions between electrons. For his contributions to quantum mechanics, he received the Nobel Prize for Physics in 1932. Heisenberg continued to be one of the leading members of the physics community and made many fundamental theoretical contributions to the physics of particle interactions and to nuclear physics. His personal reputation was damaged during the Second World War, when he continued to work in Germany at a time when many scientists quit the country.
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