Luis Walter Alvarez was born on June 13, 1911, and died on September 1, 1988. He was an American physicist, inventor, and professor who won the Nobel Prize in Physics in 1968. He was honored for discovering resonance states in particle physics using a tool called the hydrogen bubble chamber. In 2007, the American Journal of Physics said, "Luis Alvarez was one of the most brilliant and productive experimental physicists of the twentieth century."

After earning his PhD from the University of Chicago in 1936, Alvarez worked with Ernest Lawrence at the Radiation Laboratory at the University of California, Berkeley. He designed experiments to study a process called K-electron capture in radioactive atoms, which had been predicted by beta decay theory but never observed before. He used a cyclotron to create tritium and measured its lifespan. He also worked with Felix Bloch to measure the magnetic moment of the neutron.

In 1940, Alvarez joined the MIT Radiation Laboratory and helped develop radar systems for World War II. His work included improving Identification friend or foe (IFF) radar beacons, now known as transponders, and creating a system called VIXEN to prevent enemy submarines from detecting microwave radars. He is best known for designing the Ground Controlled Approach (GCA) radar system, which was important for aviation, especially during the post-war Berlin airlift. Before working on the Manhattan Project, Alvarez spent time at the University of Chicago studying nuclear reactors with Enrico Fermi. At Los Alamos, he worked under Robert Oppenheimer and helped design explosive lenses and exploding-bridgewire detonators. As part of Project Alberta, he observed the Trinity nuclear test from a B-29 Superfortress and later watched the bombing of Hiroshima from the B-29 The Great Artiste.

After the war, Alvarez helped create a liquid hydrogen bubble chamber, which allowed his team to take millions of photos of particle interactions. They developed computer systems to analyze these images and discovered new particles and resonance states. This research earned him the Nobel Prize in 1968. He also led a project to use X-rays to examine Egyptian pyramids for hidden chambers. With his son, geologist Walter Alvarez, he proposed the Alvarez hypothesis, which suggests that an asteroid impact caused the extinction of non-avian dinosaurs.

Early life

Luis Walter Alvarez was born on June 13, 1911, in San Francisco to a Catholic family. He was the second child and the oldest son of Walter C. Alvarez, a doctor, and Harriet, his wife. His grandfather, Luis F. Álvarez, was a doctor from Asturias, Spain. He lived briefly in Cuba, moved to the United States, and developed a better way to diagnose a skin disease called macular leprosy. Luis had an older sister named Gladys, a younger brother named Bob, and a younger sister named Bernice. His aunt, Mabel Alvarez, was an artist from California who painted with oil paints.

Luis attended Madison School in San Francisco from 1918 to 1924. He then went to San Francisco Polytechnic High School. In 1926, his father began working at the Mayo Clinic, and the family moved to Rochester, Minnesota. There, Luis attended Rochester High School. He had planned to study at the University of California, Berkeley, but his teachers in Rochester encouraged him to go to the University of Chicago instead. At Chicago, he earned a bachelor’s degree in 1932, a master’s degree in 1934, and a PhD in 1936. As an undergraduate, he was part of a college group called Phi Gamma Delta. Later, he joined another group called Gamma Alpha.

In 1932, while studying at the University of Chicago, Luis discovered the field of physics. He had the chance to use equipment once owned by the famous physicist Albert A. Michelson. He also built a device using Geiger counter tubes arranged like a telescope to study cosmic rays. With the help of his advisor, Arthur Compton, he conducted an experiment in Mexico City to measure the East–West effect of cosmic rays. He found that more radiation came from the west, which led him to conclude that primary cosmic rays are positively charged. Compton sent the results of this experiment to a science journal, listing Alvarez’s name first.

Luis was agnostic, even though his father had once been a deacon in a Congregational church.

Early work

Alvarez’s sister, Gladys, worked at the University of California, Berkeley, as a part-time secretary for physicist Ernest Lawrence. She told Lawrence about Alvarez, and Lawrence invited Alvarez to visit the Century of Progress exhibition in Chicago with him. After Alvarez passed his oral exams in 1936, he asked his sister to check if Lawrence had any job openings at the Radiation Laboratory. Soon, Gladys sent a telegram with a job offer from Lawrence. This began a long connection between Alvarez and the University of California, Berkeley. Alvarez and Geraldine Smithwick married in one of the chapels at the University of Chicago and then moved to California. They had two children, Walter and Jean. They divorced in 1957. On December 28, 1958, Alvarez married Janet L. Landis, and they had two more children, Donald and Helen.

At the Radiation Laboratory, Alvarez worked with Lawrence’s experimental team, which was supported by a group of theoretical physicists led by Robert Oppenheimer. Alvarez designed experiments to observe K-electron capture in radioactive nuclei, a process predicted by beta decay theory but never seen before. He used magnets to remove positrons and electrons from his radioactive sources and created a special Geiger counter to detect only the “soft” X-rays produced by K capture. He published his findings in the Physical Review in 1937.

When deuterium (hydrogen-2) is bombarded with deuterium, a fusion reaction occurs. This reaction can produce either tritium (hydrogen-3) and a proton or helium-3 and a neutron (H + H → H + p or He + n). This is one of the most basic fusion reactions and forms the basis of both thermonuclear weapons and modern research on controlled nuclear fusion. At the time, scientists did not know if the products of this reaction were stable. Based on existing theories, Hans Bethe believed tritium would be stable and helium-3 unstable. Alvarez proved the opposite by using his knowledge of the 60-inch cyclotron. He adjusted the machine to accelerate doubly ionized helium-3 nuclei, creating a beam of ions. This allowed him to use the cyclotron like a super mass spectrometer. Since the helium-3 came from deep gas wells where it had existed for millions of years, its stability was confirmed. Alvarez later used the cyclotron and the H + H reaction to produce radioactive tritium and measured its lifetime.

In 1938, Alvarez used his knowledge of the cyclotron and developed what are now called time-of-flight techniques. He created a mono-energetic beam of thermal neutrons. Using this, he began a series of experiments with Felix Bloch to measure the magnetic moment of the neutron. Their result, μ₀ = 1.93 ± 0.02 μN, published in 1940, was a major improvement over earlier studies.

World War II

In 1940, the British Tizard Mission showed American scientists how the cavity magnetron could be used to create short wavelength pulsed radar. The National Defense Research Committee, formed by President Franklin Roosevelt only months before, created a central laboratory at the Massachusetts Institute of Technology (MIT) to develop military uses of microwave radar. Lawrence quickly brought together his top scientists, including Alvarez, who joined the Radiation Laboratory at MIT on November 11, 1940. Alvarez worked on several radar projects, including improving Identification Friend or Foe (IFF) radar beacons, now called transponders, and creating a system named VIXEN to prevent enemy submarines from detecting radar signals. Enemy submarines would submerge when they sensed strong radar signals, but VIXEN sent signals that grew weaker as submarines approached, making them think planes were moving away and preventing them from submerging.

One of the first tasks was to build equipment to switch from British long-wave radar to new microwave radar made possible by the cavity magnetron. While working on the Microwave Early Warning system (MEW), Alvarez invented a linear dipole array antenna that reduced unwanted signal patterns and could be electronically scanned without mechanical movement. This was the first microwave phased-array antenna, and Alvarez used it in MEW and two other radar systems. The antenna helped the Eagle precision bombing radar guide bombs in bad weather or through clouds. Eagle was completed late in the war, and though some B-29s used it successfully, it arrived too late to change the outcome of battles.

Alvarez is best known for creating the Ground Controlled Approach (GCA) radar system, which played a major role in aviation, especially during the post-war Berlin airlift. Using Alvarez's dipole antenna, GCA allowed ground radar operators to guide planes to runways by giving verbal instructions to pilots. The system was simple and effective, even for untrained pilots. It remained in use by the military for many years after the war and was still used in some countries in the 1980s. In 1945, Alvarez was awarded the National Aeronautic Association's Collier Trophy for developing the GCA system, which helped planes land safely in all weather conditions.

In the summer of 1943, Alvarez tested GCA in England, landing planes in bad weather and training British personnel. There, he met Arthur C. Clarke, an RAF radar technician, who later wrote a novel inspired by his experiences with Alvarez. Clarke and Alvarez became close friends.

In the fall of 1943, Alvarez returned to the United States and was offered a position at Los Alamos on the Manhattan Project by Robert Oppenheimer. Oppenheimer suggested Alvarez first work with Enrico Fermi at the University of Chicago before joining Los Alamos. During this time, General Leslie Groves asked Alvarez to find a way to detect if Germany had nuclear reactors. Alvarez proposed using an airplane to detect radioactive gases like xenon-133 produced by reactors. Though the equipment flew over Germany, no xenon was found, proving the Germans had not built a working reactor. This idea of monitoring fission products for intelligence became important after the war.

Alvarez arrived at Los Alamos in 1944, later than many scientists. Work on the uranium bomb "Little Boy" was already underway, so Alvarez focused on designing the plutonium bomb "Fat Man." The method used for uranium, which involved joining two sub-critical masses with a gun-like mechanism, did not work for plutonium because spontaneous neutrons caused premature fission. Instead, scientists compressed a nearly critical plutonium sphere using explosives to create a smaller, denser core. To achieve this, thirty-two explosive charges had to be detonated simultaneously around the core. Alvarez directed his student, Lawrence H. Johnston, to use a large capacitor to power exploding-bridgewire detonators, ensuring the charges exploded within a fraction of a microsecond. This invention was crucial for the implosion-type nuclear weapon. Alvarez also supervised the RaLa Experiments.

Alvarez's final task for the Manhattan Project was to develop calibrated microphones/transmitters to measure the blast wave from atomic explosions, helping scientists calculate the bomb's energy. After being promoted to lieutenant colonel in the U.S. Army, he observed the Trinity nuclear test from a B-29 Superfortress with fellow scientists.

Flying in the B-29 "Great Artiste," Alvarez and Johnston measured the blast from the "Little Boy" bomb dropped on Hiroshima. Days later, they used the same equipment to measure the explosion over Nagasaki.

After World War II ended in 1945, Alvarez became a physics professor at the University of California, Berkeley, his first choice. In 1978, he was granted the title of professor emeritus.

Bubble chamber

After 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 ideas led to progress, the most important idea at this time came from Edwin McMillan, who introduced the concept of phase stability. This idea led to the creation of the synchrocyclotron. Improving and expanding this concept, the Lawrence team built the world's largest proton accelerator at the time, the Bevatron, which began operating in 1954. Although the Bevatron could produce many interesting particles, especially during secondary collisions, these complex interactions were difficult to detect and study at the time.

Inspired by a new tool developed by Donald Glaser called the bubble chamber, Alvarez saw its potential for visualizing particle tracks. He realized the device would be useful if it could be adapted to work with liquid hydrogen. Hydrogen nuclei, which are protons, were the simplest and most useful target for interactions with particles produced by the Bevatron. Alvarez started a program to build smaller versions of the chamber and shared his ideas with Ernest Lawrence.

The Glaser device was a small glass cylinder (1 cm × 2 cm) filled with ether. By suddenly lowering the pressure inside, the liquid could be placed into a temporary superheated state, which would boil along the path of a particle passing through. Glaser managed to keep this state for a few seconds before boiling occurred naturally. The Alvarez team built larger chambers using liquid hydrogen, made of metal with glass windows so that particle tracks could be photographed. These chambers could be cycled in sync with the accelerator beam, allowing pictures to be taken and the chamber to be recompressed for the next beam cycle.

This program built a liquid hydrogen bubble chamber nearly 7 feet (2.1 meters) long. It involved dozens of physicists, graduate students, engineers, and technicians. Millions of photographs of particle interactions were taken, and computer systems were developed to measure and analyze these interactions. This work led to the discovery of new families of particles and resonance states. Alvarez was awarded the Nobel Prize in Physics in 1968 for his key contributions to elementary particle physics, especially for discovering many resonant states through his development of hydrogen bubble chambers and data analysis techniques.

Scientific detective work

In 1964, Alvarez suggested an experiment called the High Altitude Particle Physics Experiment (HAPPE). The plan was to use a large superconducting magnet carried by a balloon to high altitude to study interactions of very high-energy particles. Over time, the experiment's focus changed to studying cosmology and the role of particles and radiation in the early universe. This work involved sending detectors to high altitudes using balloons and U-2 aircraft. It was an early version of experiments later done by the COBE satellite, which studied cosmic background radiation and earned George Smoot and John Mather the 2006 Nobel Prize.

In 1965, Alvarez proposed muon tomography to search for hidden chambers inside the Egyptian pyramids. His idea used naturally occurring cosmic rays and placed spark chambers, common tools in particle physics at the time, under the Pyramid of Khafre in a known chamber. By measuring how cosmic rays passed through the pyramid in different directions, the detector could identify any empty spaces in the surrounding rock.

Alvarez gathered a team of physicists and archaeologists from the United States and Egypt. They built the equipment and conducted the experiment, but it was paused by the 1967 Six-Day War. After the war, the project resumed, with researchers recording and analyzing cosmic rays until 1969. Alvarez then reported to the American Physical Society that no hidden chambers were found in the 19% of the pyramid examined.

In November 1966, Life magazine published photos from the 1963 "Zapruder film," which is considered the most complete record of President John F. Kennedy's assassination. Alvarez, an expert in optics and photoanalysis, studied the images and analyzed the film. He showed that the backward movement of the president's head, called the "jet-effect" theory, matched the idea that he was shot from behind. His findings were later supported by other scientists. Alvarez also studied the timing of gunshots, the shockwave that affected the camera, and the camera's speed. He noted several details that FBI analysts had missed or misunderstood. He wrote a paper to guide physicists in using scientific methods to understand the case.

Dinosaur extinction hypothesis

In 1980, Alvarez and his son, geologist Walter Alvarez, along with nuclear chemists Frank Asaro and Helen Michel, discovered a major event that changed Earth's history.

During the 1970s, Walter Alvarez studied rocks in central Italy. He found a rock layer near the Cretaceous–Paleogene boundary, where a thin clay layer was located. This clay marked the point where dinosaurs and many other species disappeared. Scientists did not understand why this happened or what the clay represented.

Alvarez worked with Frank Asaro and Helen Michel at the Lawrence Berkeley Laboratory. They used a scientific method called neutron activation analysis to study the clay. In 1980, Alvarez, Alvarez, Asaro, and Michel published an important paper suggesting that an object from space caused the Cretaceous-Paleogene extinction (then called the Cretaceous-Tertiary extinction).

After the paper was published, scientists debated its findings. Ten years later, a large impact crater was discovered off the coast of the Yucatán peninsula in Mexico, supporting the theory. Later research showed that the extinction of the dinosaurs happened quickly, over thousands of years, not millions. Other theories, such as volcanic activity at the Deccan Traps, have been proposed, but the impact crater theory is still widely accepted by scientists.

Aviation

In his book about his life, 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." A key reason for this was his love of flying. He learned to fly in 1933 and later earned special flying licenses for instrument flying and multi-engine aircraft. Over the next 50 years, he logged more than 1,000 hours of flight time, most of it as the pilot in charge. He said, "I found few things as satisfying as being pilot in charge with responsibility for my passengers' lives."

Alvarez made many important contributions to aviation. During World War II, he helped create several aviation technologies. Some of his projects, including Ground Controlled Approach (GCA), are described above. He was awarded the Collier Trophy in 1945 for his work on GCA. He also held the basic patent for the radar transponder, for which he gave the rights to the U.S. government for $1.

Later in his career, Alvarez worked on several important advisory groups related to civilian and military aviation. These groups included a Federal Aviation Administration task force studying future air navigation and air traffic control systems, the President's Science Advisory Committee Military Aircraft Panel, and a group examining how scientists could help improve the United States' ability to fight a nonnuclear war.

Alvarez's work in aviation led to many exciting experiences. For example, while working on GCA, he became the first civilian to fly a low approach with his view outside the cockpit blocked. He also flew many military aircraft from the co-pilot's seat, including a B-29 Superfortress and a Lockheed F-104 Starfighter. In addition, he survived a crash during World War II as a passenger in a Miles Master.

Death

Alvarez passed away on September 1, 1988, due to complications from several surgeries for cancer of the esophagus. His body was cremated, and his ashes were scattered in Monterey Bay. His personal papers are kept at The Bancroft Library at the University of California, Berkeley.

In popular culture

In the 1963 novel Glide Path by Sir Arthur C. Clarke, a character based on Luis Alvarez appears, though the character is not exactly the same as Alvarez. In the 2023 film Oppenheimer, directed by Christopher Nolan, Luis Alvarez is shown as a character played by actor Alex Wolff. A review titled "Collisions: The Explosive Mind of Luis Alvarez" by Banville discusses the accomplishments and life of Luis Alvarez, as well as the contributions of Hispanic scientists in the field of physics throughout history.

Honors

• Received the American Physical Society Fellowship in 1939 and served as its President in 1969
• Awarded the Collier Trophy by the National Aeronautics Association in 1946
• Became a member of the National Academy of Sciences in 1947
• Received the Medal for Merit in 1947
• Elected a Fellow of the American Philosophical Society in 1953
• Named a Fellow of the American Academy of Arts and Sciences in 1958
• Recognized as California Scientist of the Year in 1960
• Honored with the Albert Einstein Award in 1961
• Received the Golden Plate Award from the American Academy of Achievement in 1961
• Awarded the National Medal of Science in 1963
• Received the Michelson Award in 1965
• Won the Nobel Prize in Physics in 1968
• Became a member of the National Academy of Engineering in 1969
• Received the University of Chicago Alumni Medal in 1978
• Inducted into the National Inventors Hall of Fame in 1978
• Received the Enrico Fermi Award from the U.S. Department of Energy in 1987
• Granted IEEE Honorary Membership in 1988
• The Boy Scouts of America named the Cub Scout SUPERNOVA award after him in 2012
• A minor planet named 3581 Alvarez honors him and his son, Walter Alvarez.

Patents

• Tool for practicing golf
• A type of nuclear reactor that uses electrons
• A device that measures distance using light and a special prism that changes angles
• A lens made of two parts that can change magnification
• A lens system that can adjust its magnification
• A tool that detects tiny particles using a special liquid to multiply electrons
• A process to create a grid of optical elements with a Fresnel design
• An optical component that is thinner than usual
• A technique to make thinner optical components
• Explosives marked with deuterium and a way to find them
• Binoculars with zoom that stay steady
• A system that prevents collisions without needing other devices
• A person who watches TV
• Binoculars with zoom that stay steady
• A camera lens that stays steady using optical methods
• A method to find nitrogen
• A device that uses a pendulum to keep optical systems steady

General references

• Alvarez, L. W. (1987). Alvarez: Adventures of a Physicist. Published by Basic Books. ISBN 0-465-00115-7. Available through the Internet Archive.
• Heilbron, J. L.; Seidel, R. W. (1989). Lawrence and His Laboratory. Published by the University of California Press. ISBN 0-520-06426-7.
• Trower, W. P. (2009). Luis Walter Alvarez 1911–1988 (PDF). Published in the Biographical Memoirs by the National Academy of Sciences. Retrieved on March 21, 2013.
• Trower, W. P. (1987). Discovering Alvarez: Selected Works of Luis W. Alvarez with Commentary by His Students and Colleagues. Published by the University of Chicago Press. ISBN 0-226-81304-5.