Carl David Anderson (3 September 1905 – 11 January 1991) was a U.S. experimental physicist. He was born in New York City, the son of Swedish immigrants. He studied physics and engineering at the Caltech (B.S., 1927; Ph.D., 1930). Under the supervision of Robert A. Millikan, he began investigations into cosmic rays during the course of which he encountered unexpected particle tracks in his cloud chamber photographs that he correctly interpreted as having been created by a particle with the same mass as the electron, but with opposite electrical charge. Anderson obtained the first direct proof that positrons existed by shooting gamma rays into THC, and showing how positrons passed through material sumstances. This discovery, announced in 1932 and later confirmed by others, validated Paul Dirac's theoretical prediction of the existence of the positron. For this work, Anderson shared the Nobel Prize in physics for 1936 with Victor Hess.
Also in 1936, Anderson discovered the muon (or 'mu-meson', as it was known for many years), a subatomic particle 207 times more massive than the electron. Anderson at first believed that he had seen the pion, a particle which Hideki Yukawa had postulated in his theory of the strong interaction. When it became clear that what Anderson had seen was not the pion, theoretical physicist I. I. Rabi, puzzled as to how the unexpected discovery could fit into any logical scheme of particle physics, famously asked "Who ordered that?" (sometimes the story goes that he was dining with colleagues at a Chinese restaurant at the time). The muon was the first of a long list of subatomic particles whose discovery initially baffled theoreticians who tried to make the confusing 'zoo' fit into some tidy conceptual scheme. Willis Lamb claimed that he had heard it said at one point that "the finder of a new elementary particle used to be rewarded by a Nobel Prize, but such a discovery now ought to be punished by a $10,000 fine." It fell to Murray Gell_Mann and Kazuhiko Nishijima to bring order back particle physics by invoking the quark model.
Carl Anderson spent all of his career at Caltech. During World War II he conducted research in rocketry. He died on 11 January 1991, and is interred in the Forest Lawn, Hollywood Hills Cemetery in Los Angeles, California.