Louis Alvarez

Publication of the 1980 paper brought criticism from the geologic community, and an often acrimonious scientific debate ensued. Ten years later, and after Alvarez's death, evidence of a large impact crater called Chicxulub was found off the coast of Mexico, providing support for the theory. Other researchers later found that the end-Cretaceous extinction of the dinosaurs may have occurred rapidly in geologic terms, over thousands of years, rather than millions of years as had previously been supposed. Others continue to study alternative extinction causes such as increased volcanism, particularly the massive Deccan Traps eruptions that occurred around the same time, and climate change, checking against the fossil record. However, on March 4, 2010, a panel of 41 scientists agreed that the Chicxulub asteroid impact triggered the mass extinction.

Alvarez died on September 1, 1988, due to complications from a succession of recent operations for esophageal cancer. His remains were cremated, and his ashes were scattered over Monterey Bay. His papers are in The Bancroft Library at the University of California, Berkeley.

The radar system for which Alvarez is best known and which has played a major role in aviation, most particularly in the post war Berlin airlift, was Ground Controlled Approach (GCA). Using Alvarez's dipole antenna to achieve a very high angular resolution, GCA allows ground-based radar operators watching special precision displays to guide a landing airplane to the runway by transmitting verbal commands to the pilot. The system was simple, direct, and worked well, even with previously untrained pilots. It was so successful that the military continued to use it for many years after the war, and it was still in use in some countries in the 1980s. Alvarez was awarded the National Aeronautic Association's Collier Trophy in 1945 "for his conspicuous and outstanding initiative in the concept and development of the Ground Control Approach system for safe landing of aircraft under all weather and traffic conditions".

Louis Alvarez began making documentaries while living in New Orleans in the 1970s. It was there he met his longtime producing partner Andrew Kolker and set out to make a series of films on Louisiana culture.

After the war Alvarez was involved in the design of a liquid hydrogen bubble chamber that allowed his team to take millions of photographs of particle interactions, develop complex computer systems to measure and analyze these interactions, and discover entire families of new particles and resonance states. This work resulted in his being awarded the Nobel Prize in 1968. He was involved in a project to x-ray the Egyptian pyramids to search for unknown chambers. With his son, geologist Walter Alvarez, he developed the Alvarez hypothesis which proposes that the extinction event that wiped out the non-avian dinosaurs was the result of an asteroid impact.

Alvarez assembled a team of physicists and archeologists from the United States and Egypt, the recording equipment was constructed and the experiment carried out, though it was interrupted by the 1967 Six-Day War. Restarted after the war, the effort continued, recording and analyzing the penetrating cosmic rays until 1969 when Alvarez reported to the American Physical Society that no chambers had been found in the 19% of the pyramid surveyed.

In November 1966 Life published a series of photographs from the film that Abraham Zapruder took of the Kennedy assassination. Alvarez, an expert in optics and photoanalysis, became intrigued by the pictures and began to study what could be learned from the film. Alvarez attempted to demonstrate both in theory and experiment that the backward snap of the President's head was consistent with his being shot from behind, but his work on the so-called "jet-effect" has been discredited, due to his demonstrably poor methodology - see Last Second in Dallas by Josiah Thompson. He also investigated the timing of the gunshots and the shockwave which disturbed the camera, and the speed of the camera, pointing out a number of things which the FBI photo analysts either overlooked or got wrong. He produced a paper intended as a tutorial, with informal advice for the physicist intent on arriving at the truth.

Alvarez proposed Muon tomography in 1965 to search the Egyptian pyramids for unknown chambers. Using naturally occurring cosmic rays, his plan was to place spark chambers, standard equipment in the high-energy particle physics of this time, beneath the Pyramid of Khafre in a known chamber. By measuring the counting rate of the cosmic rays in different directions the detector would reveal the existence of any void in the overlaying rock structure.

In 1964 Alvarez proposed what became known as the High Altitude Particle Physics Experiment (HAPPE), originally conceived as a large superconducting magnet carried to high altitude by a balloon in order to study extremely high-energy particle interactions. In time the focus of the experiment changed toward the study of cosmology and the role of both particles and radiation in the early universe. This work was a large effort, carrying detectors aloft with high-altitude balloon flights and high-flying U-2 aircraft, and an early precursor of the COBE satellite-born experiments on the cosmic background radiation (which resulted in the award of the 2006 Nobel Prize, shared by George Smoot and John Mather.)

Alvarez's sister, Gladys, worked for Ernest Lawrence as a part-time secretary, and mentioned Alvarez to Lawrence. Lawrence then invited Alvarez to tour the Century of Progress exhibition in Chicago with him. After he completed his oral exams in 1936, Alvarez, now engaged to be married to Geraldine Smithwick, asked his sister to see if Lawrence had any jobs available at the Radiation Laboratory. A telegram soon arrived from Gladys with a job offer from Lawrence. This started a long association with the University of California, Berkeley. Alvarez and Smithwick were married in one of the chapels at the University of Chicago and then headed for California. They had two children, Walter and Jean. They were divorced in 1957. On December 28, 1958, he married Janet L. Landis, and had two more children, Donald and Helen.

Returning to the University of California, Berkeley as a full professor, Alvarez had many ideas about how to use his wartime radar knowledge to improve particle accelerators. Though some of these were to bear fruit, the "big idea" of this time would come from Edwin McMillan with his concept of phase stability which led to the synchrocyclotron. Refining and extending this concept, the Lawrence team would build the world's then-largest proton accelerator, the Bevatron, which began operating in 1954. Though the Bevatron could produce copious amounts of interesting particles, particularly in secondary collisions, these complex interactions were hard to detect and analyze at the time.

Alvarez made numerous professional contributions to aviation. During World War II he led the development of multiple aviation-related technologies. Several of his projects are described above, including Ground Controlled Approach (GCA) for which he was awarded the Collier Trophy in 1945. He also held the basic patent for the radar transponder, for which he assigned rights to the U.S. government for $1.

As a result of his radar work and the few months spent with Fermi, Alvarez arrived at Los Alamos in the spring of 1944, later than many of his contemporaries. The work on the "Little Boy" (a uranium bomb) was far along so Alvarez became involved in the design of the "Fat Man" (a plutonium bomb). The technique used for uranium, that of forcing the two sub-critical masses together using a type of gun, would not work with plutonium because the high level of background spontaneous neutrons would cause fissions as soon as the two parts approached each other, so heat and expansion would force the system apart before much energy has been released. It was decided to use a nearly critical sphere of plutonium and compress it quickly by explosives into a much smaller and denser core, a technical challenge at the time.

Alvarez spent the summer of 1943 in England testing GCA, landing planes returning from battle in bad weather, and also training the British in the use of the system. While there he encountered the young Arthur C. Clarke, who was an RAF radar technician. Clarke subsequently used his experiences at the radar research station as the basis for his novel Glide Path, which contains a thinly disguised version of Alvarez. Clarke and Alvarez developed a long-term friendship.

In 1940, Alvarez joined the MIT Radiation Laboratory, where he contributed to a number of World War II radar projects, from early improvements to Identification friend or foe (IFF) radar beacons, now called transponders, to a system known as VIXEN for preventing enemy submarines from realizing that they had been found by the new airborne microwave radars. Enemy submarines would wait until the radar signal was getting strong and then submerge, escaping attack. But VIXEN transmitted a radar signal whose strength was the cube of the distance to the submarine so that as they approached the sub, the signal—as measured by the sub—got progressively weaker, and the sub assumed the plane was getting farther away and didn't submerge. The radar system for which Alvarez is best known and which has played a major role in aviation, most particularly in the post war Berlin airlift, was Ground Controlled Approach (GCA). Alvarez spent a few months at the University of Chicago working on nuclear reactors for Enrico Fermi before coming to Los Alamos to work for Robert Oppenheimer on the Manhattan project. Alvarez worked on the design of explosive lenses, and the development of exploding-bridgewire detonators. As a member of Project Alberta, he observed the Trinity nuclear test from a B-29 Superfortress, and later the bombing of Hiroshima from the B-29 The Great Artiste.

In 1938, again using his knowledge of the cyclotron and inventing what are now known as time-of-flight techniques, Alvarez created a mono-energetic beam of thermal neutrons. With this he began a long series of experiments, collaborating with Felix Bloch, to measure the magnetic moment of the neutron. Their result of μ0 = 1.93± 0.02 μN , published in 1940, was a major advance over earlier work.

At the Radiation Laboratory he worked with Lawrence's experimental team, which was supported by a group of theoretical physicists headed by Robert Oppenheimer. Alvarez devised a set of experiments to observe K-electron capture in radioactive nuclei, predicted by the beta decay theory but never observed. Using magnets to sweep aside the positrons and electrons emanating from his radioactive sources, he designed a special purpose Geiger counter to detect only the "soft" X-rays coming from K capture. He published his results in the Physical Review in 1937.

After receiving his PhD from the University of Chicago in 1936, Alvarez went to work for Ernest Lawrence at the Radiation Laboratory at the University of California, Berkeley. Alvarez devised a set of experiments to observe K-electron capture in radioactive nuclei, predicted by the beta decay theory but never before observed. He produced tritium using the cyclotron and measured its lifetime. In collaboration with Felix Bloch, he measured the magnetic moment of the neutron.

In his autobiography, Alvarez said, "I think of myself as having had two separate careers, one in science and one in aviation. I've found the two almost equally rewarding." An important contributor to this was his enjoyment of flying. He learned to fly in 1933, later earning instrument and multi-engine ratings. Over the next 50 years he accumulated over 1000 hours of flight time, most of it as pilot in command. He said, "I found few activities as satisfying as being pilot in command with responsibility for my passengers' lives."

In 1932, as a graduate student at Chicago, he discovered physics there and had the rare opportunity to use the equipment of legendary physicist Albert A. Michelson. Alvarez also constructed an apparatus of Geiger counter tubes arranged as a cosmic ray telescope, and under the aegis of his faculty advisor Arthur Compton, conducted an experiment in Mexico City to measure the so-called East–West effect of cosmic rays. Observing more incoming radiation from the west, Alvarez concluded that primary cosmic rays were positively charged. Compton submitted the resulting paper to the Physical Review, with Alvarez's name at the top.

He attended Madison School in San Francisco from 1918 to 1924, and then San Francisco Polytechnic High School. In 1926, his father became a researcher at the Mayo Clinic, and the family moved to Rochester, Minnesota, where Alvarez attended Rochester High School. He had always expected to attend the University of California, Berkeley, but at the urging of his teachers at Rochester, he instead went to the University of Chicago, where he received his bachelor's degree in 1932, his master's degree in 1934, and his PhD in 1936. As an undergraduate, he belonged to the Phi Gamma Delta fraternity. As a postgraduate he moved to Gamma Alpha.

Luis Walter Alvarez (June 13, 1911 – September 1, 1988) was an American experimental physicist, inventor, and professor who was awarded the Nobel Prize in Physics in 1968 for development of the hydrogen bubble chamber enabling discovery of resonance states in particle physics. The American Journal of Physics commented, "Luis Alvarez was one of the most brilliant and productive experimental physicists of the twentieth century."