The Physical World.

Physics arguably got one of its great boosts in the 1930s thanks to work in the United States and Europe. However, the flow of scientists fleeing European dictatorships for the United States also contributed substantially to progress in America. Cosmic rays constituted a subject of interest in astrophysics, as Carl David Anderson in 1932 confirmed the existence of the antielectron, or positron, whose existence the British physicist P. A. M. Dirac had predicted. Pursuing research together with Seth Neddermayer, Anderson discovered the existence of another particle in 1937, which he first called a meson; its mass was greater than that of the electron but smaller than that of the proton. This discovery caused several problems in the establishment of experimental conditions in a particle accelerator; since the direction of these particles' energy could not be predicted, detectors might not react with...