Alvarez, Luis W. 1911-1988

ALVAREZ, LUIS W. 1911-1988

Physicist

Background

Luis Alvarez, winner of the 1968 Nobel Prize for physics, was born in San Francisco on 13 June 1911. A graduate of the University of Chicago, Alvarez's intellectual interests spanned a variety of scientific fields. During World War II Alvarez was a group leader among scientists who developed the atomic bomb, and he was one of a select few observers who flew in a companion aircraft with the Enola Gay to witness the detonation of the atomic bomb over Hiroshima on 6 August 1945. During the early years of the war Alvarez, then working at the Massachusetts Institute of Technology, developed a radar system that assisted aircraft in landing during heavy fog and other low-visibility circumstances. In 1946 Alvarez developed the proton linear accelerator known as LINEAC using tubular wave guides and other components. Using his invention, scientists were able to accelerate protons to a speed of 32 MeV. After World War II he returned to the University of California, Berkeley and began the work with cloud chambers that resulted in his Nobel Prize.

Bubble Chamber Experiments

In his work with, and development of, liquid hydrogen cloud chambers in the mid 1950s, Alvarez experimented with atomic and subatomic particles and mapped out many of their properties. He found that when atomic particles passed through a cloud chamber—a dish-sized container, its walls blackened, in which hydrogen liquid, kept near its boiling point, sat in a magnetic field—atomic particles that passed through the chamber would cause wisps of evaporating hydrogen to leave a trail of bubbles behind. From the patterns of these trails Alvarez was able to deduce many properties of the subatomic particles. Among his discoveries with the bubble chamber were tritium, as well as ephemeral meson and baryon particles.

Photographing a Pyramid

During the 1960s Alvarez applied his knowledge of high-energy physics to a question that had long haunted archaeologists. Most pyramids had been found to contain secret, treasure-laden chambers at their cores. In the Egyptian pyramid Chephren, however, archaeologists had been unable to discover such a chamber. Alvarez devised a system using sensitive detectors placed underneath the pyramid to "photograph" cosmic ray (radiation from the sun) absorption patterns in the pyramid's structure. If the original Egyptian architects had devised a hidden chamber it would show up in the detectors under the pyramid as a bright spot in the cosmic ray absorption patterns. The results of Alvarez's experiment, in which no such bright spots were detected, confirmed the suspicions of archaeologists that, in the Chephren pyramid at least, there was no hidden chamber.

Theory of the Dinosaurs' Extinction

In 1981 Alvarez and his son Walter proposed the view that dinosaurs had become extinct after a giant meteorite smashed into the earth 65 million years ago. Their theory had its genesis in geologic explorations done by Walter Alvarez in Italy during the 1970s. Walter had noted that an iridium-rich sediment little more than an inch thick was to be found in layers of earth situated between the Cretaceous and the Tertiary periods' geologic strata. Recognizing that meteorites generally contain high levels of iridium, the fatherson team postulated that a gigantic meteorite—perhaps an asteroid or comet—smashed into the planet 65 million years ago. A cloud of dust was thrown into the upper atmosphere, causing temperatures on the planet's surface to plummet. The atmospheric changes associated with the impact choked off the sunlight needed by the cold-blooded dinosaurs to keep their body temperatures up and disturbed or destroyed food sources. After conducting a series of geochemical studies of rock strata which confirmed the view, the elder Alvarez chided a group of paleontologists who disagreed with his conclusions: "I don't like to say bad things about paleontologists, but they're not very good scientists.…They're more like stamp collectors."

Sources:

Luis R. Alvarez, Alvarez: Adventures of a Physicist (New York: Basic Books, 1987);

Discovering Alvarez: Selected Works of Luis W. Alvarez (Chicago: University of Chicago Press, 1987).