June - Rutherford speculates on the existence of the neutron at a lecture to the Royal Society of London.
Werner Heisenberg, Max Born and later Erwin Schrödinger formulate quantum mechanics. Heisenberg is awarded the Nobel Prize in Physics in 1932 for the creation of quantum mechanics.
Werner Heisenberg states the uncertainty principle, which states that it is not possible to simultaneously determine the position and momentum of a particle.
Ernest O. Lawrence conceives idea for the first cyclotron, a device that greatly increased the speed with which protons could be hurled at atomic nuclei. He was awarded the 1939 Nobel Prize in Physics for the invention and development of the cyclotron and for results obtained with it. John Crockcroft and E. T. S. Walton develop a high-voltage apparatus ("linear accelerator") for accelerating protons. With this they study nuclear reactions (atomic transmutation) and are awarded the 1951 Nobel Prize in Physics.