Born on 13 June 1911 in San Francisco, Luis Alvarez was a Nobel-winning experimental physicist whose discoveries ranged from nuclear and particle physics to the history of Earth’s mass extinctions. He started as a chemistry student at the University of Chicago but quickly switched to physics. In the late 1930s he made a series of important discoveries, such as measuring the magnetic moment of the neutron and determining that tritium (a hydrogen atom with two neutrons) is radioactive (see the article by Alvarez, Physics Today, January 1982, page 25). During World War II Alvarez developed radar systems for aircraft and detonators for the plutonium bomb; he was on a plane flying in formation with the Enola Gay during the Hiroshima bombing. After the war Alvarez discovered many new composite particles using a bubble chamber filled with liquid hydrogen. That research earned him the 1968 Nobel Prize in Physics. Late in his career, Alvarez teamed up with his son Walter, a geologist. The two scientists discovered an iridium isotope between sediment layers from the Cretaceous and Tertiary periods. The researchers concluded that the iridium came from a meteor impact about 65 million years ago, a catastrophic event that wiped out the dinosaurs and many other species (see the article by Alvarez, Physics Today, July 1987, page 24). After plenty of initial skepticism, that theory is widely accepted today. Alvarez died in 1988 at age 77. (Photo credit: Jerome Danburg, courtesy AIP Emilio Segrè Visual Archives, Danburg Collection)
