Werner Heisenberg dies in Munich, Germany. Werner Heisenberg was a primary physicists behind the development of Quantum Physics, one of the most important and successful scientific theories of the 20th century.
Heisenberg's work was integrated with that of Niels Bohr to create the Bohr-Heisenberg interpretation of the consequences of Quantum Physics, an interpretation more commonly known as the Copenhagen Interpretation. Heisenberg has become best known popularly for his Uncertainty Principle.
According to the Heisenberg Uncertainty Principle, it is impossible to exactly measure both the position and the momentum of an electron at the same time. It is possible to know one or the other, but the more exactly one is determined the more uncertain the other necessarily becomes.
Werner Heisenberg argued that this is not simply due to errors or limitations in our scientific instruments, such that improvements over time might eventually lead to more accurate measurements of both. Instead, this uncertainty is due to the fact that electrons don't even have exact momentum and position.