American physicist, inventor and professor (1911–1988)
This article is about the American physicist. For his grandfather, the Spanish physician, seeLuis F. Álvarez. For other people of the same name, seeLuis Álvarez (disambiguation).
After the war Alvarez was involved in the design of aliquid hydrogenbubble 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 tox-ray theEgyptian pyramids to search for unknown chambers. With his son, geologistWalter Alvarez, he developed theAlvarez hypothesis which proposes that theextinction event that wiped out the non-avian dinosaurs was the result of an asteroid impact.
Luis Walter Alvarez was born into aRoman Catholic family in San Francisco on June 13, 1911, the second child and oldest son ofWalter C. Alvarez, a physician, and his wife Harriet née Smyth, and a grandson ofLuis F. Álvarez, a Spanish physician, born in Asturias, Spain, who lived in Cuba for a while and finally settled in the United States, who found a better method for diagnosingmacular leprosy. He had an older sister, Gladys, a younger brother, Bob, and a younger sister, Bernice.[3] His aunt,Mabel Alvarez, was a California artist specializing inoil painting.[4]
In 1932, as agraduate student at Chicago, he discovered the field of physics and had the rare opportunity to use the equipment of legendary physicistAlbert A. Michelson.[9] Alvarez also constructed an apparatus ofGeiger counter tubes arranged as acosmic ray telescope, and under the aegis of his faculty advisorArthur Compton, conducted an experiment in Mexico City to measure the so-calledEast–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 thePhysical Review, with Alvarez's name at the top.[10]
Alvarez was an agnostic even though his father had been a deacon in a Congregational church.[11][12]
Nobel LaureateArthur Compton, left, with young graduate student Luis Alvarez at the University of Chicago in 1933. Compton served as his doctoral adviser.
Alvarez's sister, Gladys, worked for Berkeley physicistErnest Lawrence as a part-time secretary, and mentioned Alvarez to Lawrence. Lawrence then invited Alvarez to tour theCentury of Progress exhibition in Chicago with him.[13] After he completed hisoral exams in 1936, Alvarez, now engaged to be married to Geraldine Smithwick, asked his sister to see if Lawrence had any jobs available at theRadiation Laboratory. A telegram soon arrived from Gladys with a job offer from Lawrence. This started a long association with theUniversity of California, Berkeley. Alvarez and Smithwick were married in one of the chapels at the University of Chicago and then headed for California.[14] They had two children,Walter and Jean.[15] They were divorced in 1957. On December 28, 1958, he married Janet L. Landis, and had two more children, Donald and Helen.[16]
At the Radiation Laboratory he worked with Lawrence's experimental team, which was supported by a group of theoretical physicists headed byRobert Oppenheimer.[17] Alvarez devised a set of experiments to observe K-electron capture inradioactive nuclei, predicted by thebeta decay theory but never observed. Usingmagnets to sweep aside thepositrons andelectrons 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 thePhysical Review in 1937.[18][19]
Whendeuterium (hydrogen-2) is bombarded with deuterium, thefusion reaction yields eithertritium (hydrogen-3) plus aproton orhelium-3 plus aneutron (2 H +2 H →3 H + p or3 He + n). This is one of the most basicfusion reactions, and the foundation of thethermonuclear weapon and the current research oncontrolled nuclear fusion. At that time the stability of these two reaction products was unknown, but based on existing theoriesHans Bethe thought that tritium would be stable and helium-3 unstable. Alvarez proved the reverse by using his knowledge of the details of the 60-inchcyclotron operation. He tuned the machine to accelerate doubly ionized helium-3 nuclei and was able to get abeam of accelerated ions, thus using the cyclotron as a kind of supermass spectrometer. As the accelerated helium came from deepgas wells where it had been for millions of years, the helium-3 component had to be stable. Afterwards Alvarez produced the radioactive tritium using the cyclotron and the2 H +2 H reaction and measured its lifetime.[20][21][22]
In 1938, again using his knowledge of the cyclotron and inventing what are now known astime-of-flight techniques, Alvarez created a mono-energetic beam ofthermal neutrons. With this he began a long series of experiments, collaborating withFelix Bloch, to measure themagnetic moment of the neutron. Their result ofμ0 =1.93±0.02 μN, published in 1940, was a major advance over earlier work.[23]
The BritishTizard Mission to the United States in 1940 demonstrated to leading American scientists the successful application of thecavity magnetron to produce short wavelength pulsedradar. TheNational Defense Research Committee, established only months earlier by PresidentFranklin Roosevelt, created a central national laboratory at theMassachusetts Institute of Technology (MIT) for the purpose of developing military applications of microwave radar. Lawrence immediately recruited his best "cyclotroneers", among them Alvarez, who joined this new laboratory, known as theRadiation Laboratory, on November 11, 1940.[24] Alvarez contributed to a number ofradar projects, from early improvements toIdentification Friend or Foe (IFF) radar beacons, now calledtransponders, to a system known as VIXEN for preventing enemy submarines from realizing that they had been found by the new airborne microwave radars.[25] 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 did not submerge.[26][27]
One of the first projects was to build equipment to transition from the British long-wave radar to the new microwave centimeter-band radar made possible by thecavity magnetron. In working on theMicrowave Early Warning system (MEW), Alvarez invented alinear dipole array antenna that not only suppressed the unwantedside lobes of the radiation field but also could be electronically scanned without the need for mechanical scanning. This was the first microwave phased-array antenna, and Alvarez used it not only in MEW but in two additional radar systems. The antenna enabled the Eagleprecision bombing radar to support precision bombing in bad weather or through clouds. It was completed rather late in the war; although a number ofB-29s were equipped with Eagle and it worked well, it came too late to make much difference.[28]
The radar system for which Alvarez is best known and which has played a major role in aviation, most particularly in the post-warBerlin airlift, wasGround Controlled Approach (GCA). Using Alvarez's dipole antenna to achieve a very highangular resolution, GCA allows ground-based radar operators to watch 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.[29] Alvarez was awarded theNational Aeronautic Association'sCollier 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".[30][31]
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 youngArthur C. Clarke, who was an RAF radar technician. Clarke subsequently used his experiences at the radar research station as the basis for his novelGlide Path, which contains a thinly disguised version of Alvarez.[32] Clarke and Alvarez developed a long-term friendship.[33]
In the fall of 1943, Alvarez returned to the United States with an offer fromRobert Oppenheimer to work atLos Alamos on theManhattan Project. However, Oppenheimer suggested that he first spend a few months at theUniversity of Chicago working withEnrico Fermi before coming to Los Alamos. During these months, GeneralLeslie Groves asked Alvarez to think of a way that the US could find out if the Germans were operating anynuclear reactors, and, if so, where they were. Alvarez suggested that an airplane could carry a system to detect the radioactive gases that a reactor produces, particularlyxenon-133. The equipment did fly over Germany, but detected no radioactive xenon because the Germans had not built a reactor capable of a chain reaction. This was the first idea of monitoringfission products forintelligence gathering. It would become extremely important after the war.[34]
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 atype of gun, would not work with plutonium because the high level of backgroundspontaneous 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 ofplutonium and compress it quickly by explosives into a much smaller and densercore, a technical challenge at the time.[35]
To create the symmetricalimplosion required to compress the plutonium core to the required density, thirty-two explosive charges were to be simultaneously detonated around the spherical core. Using conventional explosive techniques withblasting caps, progress towards achieving simultaneity to within a small fraction of a microsecond was discouraging. Alvarez directed his graduate student,Lawrence H. Johnston, to use a largecapacitor to deliver ahigh voltage charge directly to eachexplosive lens, replacing blasting caps withexploding-bridgewire detonators. The exploding wire detonated the thirty-two charges to within a few tenths of a microsecond. The invention was critical to the success of theimplosion-type nuclear weapon. He also supervised theRaLa Experiments.[36] Alvarez later wrote that:
With modern weapons-grade uranium, the background neutron rate is so low that terrorists, if they had such material, would have a good chance of setting off a high-yield explosion simply by dropping one half of the material onto the other half. Most people seem unaware that if separatedU-235 is at hand, it's a trivial job to set off a nuclear explosion, whereas if only plutonium is available, making it explode is the most difficult technical job I know.[37]
Following the conclusion of theSecond World War in 1945 Alvarez would become a professor of physics at the school he had originally desired to attend, the University of California, Berkeley and in 1978 he would be granted the title of professor emeritus.[41]
Celebrating winning the Nobel Prize, October 30, 1968. The balloons are inscribed with the names of subatomic particles that his group discovered.
Returning to the University of California, Berkeley as afull professor, Alvarez had many ideas about how to use his wartime radar knowledge to improveparticle accelerators. Though some of these were to bear fruit, the "big idea" of this time would come fromEdwin McMillan with his concept ofphase stability which led to thesynchrocyclotron. Refining and extending this concept, the Lawrence team would build the world's then-largest proton accelerator, theBevatron, 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.[42]
Seizing upon a new development to visualize particle tracks, created byDonald Glaser and known as abubble chamber, Alvarez realized the device was just what was needed, if only it could be made to function withliquid hydrogen.Hydrogen nuclei, which areprotons, made the simplest and most desirable target for interactions with the particles produced by the Bevatron. He began a development program to build a series of small chambers, and championed the device to Ernest Lawrence.[43]
The Glaser device was a small glass cylinder (1 cm × 2 cm) filled withether. By suddenly reducing the pressure in the device, the liquid could be placed into a temporarysuperheated state, which would boil along the disturbed track of a particle passing through. Glaser was able to maintain the superheated state for a few seconds before spontaneous boiling took place. The Alvarez team built chambers of 1.5 in, 2.5 in, 4 in, 10 in, and 15 in using liquid hydrogen, and constructed of metal with glass windows, so that the tracks could be photographed. The chamber could be cycled in synchronization with the accelerator beam, a picture could be taken, and the chamber recompressed in time for the next beam cycle.[44]
This program built a liquid hydrogen bubble chamber almost 7 feet (2.1 meters) long, employed dozens of physicists and graduate students together with hundreds of engineers and technicians, took millions of photographs of particle interactions, developed computer systems to measure and analyze the interactions, and discovered families of new particles andresonance states. This work resulted in theNobel Prize in Physics for Alvarez in 1968,[45] "For his decisive contributions to elementary particle physics, in particular the discovery of a large number of resonant states, made possible through his development of the technique of using hydrogen bubble chambers and data analysis."[46]
X-Raying the Pyramids with EgyptologistAhmed Fakhry and Team Leader Jerry Anderson, Berkeley, 1967
In 1964, Alvarez proposed what became known as theHigh Altitude Particle Physics Experiment (HAPPE), originally conceived as a largesuperconducting magnet carried to high altitude by aballoon in order to study extremely high-energy particle interactions.[47] In time the focus of the experiment changed toward the study ofcosmology and the role of both particles and radiation in theearly universe. This work was a large effort, carrying detectors aloft withhigh-altitude balloon flights and high-flyingU-2 aircraft, and an early precursor of theCOBE satellite-born experiments on the cosmic background radiation (which resulted in the award of the 2006 Nobel Prize, shared byGeorge Smoot andJohn Mather[47]).
Alvarez proposedmuon tomography in 1965 to search theEgyptian pyramids for unknown chambers. Using naturally occurringcosmic rays, his plan was to placespark chambers, standard equipment in the high-energyparticle physics of this time, beneath thePyramid 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.[48]
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 1967Six-Day War. Restarted after the war, the effort continued, recording and analyzing the penetrating cosmic rays until 1969, when he reported to theAmerican Physical Society that no chambers had been found in the 19% of the pyramid surveyed.[49]
In November 1966,Life magazine published a series of photographs from the 1963 "Zapruder film", believed to be the most complete document of theassassination of John F. Kennedy. Alvarez, an expert in optics andphotoanalysis, became intrigued by the pictures and began to study what could be learned from the film. Alvarez demonstrated both in theory and experiment that the backward snap of the President's head was consistent with his being shot from behind being called the "jet-effect" theory. Alvarez's theory was later refined and corroborated by other researchers.[50][51] Alvarez also investigated the timing of the gunshots and the shockwave that disturbed the camera, and the speed of the camera, pointing out a number of details that 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 of the case.[52]
In 1980 Alvarez and his son, geologistWalter Alvarez, along with nuclear chemistsFrank Asaro andHelen Michel, "uncovered a calamity that literally shook the Earth and is one of the great discoveries about Earth's history".[2]
During the 1970s, Walter Alvarez was doing geologic research in central Italy. There he had located an outcrop on the walls of a gorge whoselimestone layers includedstrata both above and below theCretaceous–Paleogene boundary. Exactly at the boundary is a thin layer ofclay. Walter told his father that the layer marked where thedinosaurs and much else became extinct and that nobody knew why, or what the clay was about—it was a big mystery, and he intended to solve it.[2]
Alvarez had access to thenuclear chemists at theLawrence Berkeley Laboratory and was able to work withFrank Asaro andHelen Michel, who used the technique ofneutron activation analysis to study the clay. In 1980, Alvarez, Alvarez, Asaro, and Michel published a seminal paper proposing an extraterrestrial cause for the Cretaceous-Paleogene extinction (then called the Cretaceous-Tertiary extinction).[53] In the years following the publication of their article, the clay was also found to containsoot,glassy spherules,shocked quartz crystals, microscopicdiamonds, and rare minerals formed only under conditions of great temperature and pressure.[2]
Publication of the 1980 paper brought criticism from the geologic community, and an often acrimonious scientific debate ensued. Ten years later, after Alvarez's death, evidence was found of a largeimpact crater off the coast of the Yucatán peninsula in Mexico, providing support for the theory. Other researchers later found that theend-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. While alternative extinction theories have been proposed, including increasedvolcanism at theDeccan Traps, the impact crater theory remains dominant among relevant scholars.[54]
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 earninginstrument and multi-engine ratings. Over the next 50 years he accumulated over 1000 hours of flight time, most of it as pilot in command.[55] He said, "I found few activities as satisfying as being pilot in command with responsibility for my passengers' lives."[56]
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 radartransponder, for which he assigned rights to the U.S. government for $1.[55]
Later in his career Alvarez served on multiple high level advisory committees related to civilian and military aviation. These included aFederal Aviation Administration task group on futureair navigation andair traffic control systems, thePresident's Science Advisory Committee Military Aircraft Panel, and a committee studying how the scientific community could help improve the United States' capabilities for fighting a nonnuclear war.[57]
Alvarez's aviation responsibilities led to many adventures. For example, while working on GCA he became the first civilian to fly a low approach with his view outside the cockpit obstructed. He also flew many military aircraft from the co-pilot's seat, including aB-29 Superfortress[56] and aLockheed F-104 Starfighter.[58] In addition, he survived a crash during World War II as a passenger in aMiles Master.[59]
"Collisions" review: The Explosive Mind of Luis Alvarez" Banville highlighted the achievements and life of the Hispanic physical community throughout history.[65]
^Alvarez: adventures of a physicist. Basic Books. 1987. p. 279.ISBN9780465001156. "Physicists feel that the subject of religion is taboo. Almost all consider themselves agnostics. We talk about the big bang that started the present universe and wonder what caused it and what came before. To me the idea of a Supreme Being is attractive, but I'm sure that such a Being isn't the one described in any holy book. Since we learn about people by examining what they have done, I conclude that any Supreme Being must have been a great mathematician. The universe operates with precision according to mathematical laws of enormous complexity. I'm unable to identify its creator with the Jesus to whom my maternal grandparents, missionaries in China, devoted their lives."
^Alvarez, Luis W. (March 4, 1958). "Golf training device". U.S. Patent No. 2,825,569. Washington, DC: U.S. Patent and Trademark Office.
^Lawrence, E. O., McMillan, E. M., & Alvarez, L. W. (1960). Electronuclear Reactor (No. US 2933442).
^Alvarez, L. W. (January 24, 1967). "Optical range finder with variable angle exponential prism". U.S. Patent No. 3,299,768. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, Luis W. (February 21, 1967). "Two-element variable-power spherical lens". U.S. Patent 3,305,294. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, Luis W., and William E. Humphrey. (April 21, 1970). "Variable-power lens and system". U.S. Patent No. 3,507,565. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, Luis W., Stephen E. Derenzo, Richard A. Muller, Robert G. Smits, and Haim Zaklad. (April 25, 1972). "Subatomic particle detector with liquid electron multiplication medium". U.S. Patent No. 3,659,105. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, L. (June 19, 1973). "Method of making fresnelled optical element matrix". U.S. Patent No. 3,739,455. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, L. (August 6, 1974). "Optical element of reduced thickness". U.S. Patent No. 3,827,798. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, L. (August 13, 1974). "Method of forming an optical element of reduced thickness". U.S. Patent No. 3,829,536. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, Luis W.,(February 17, 1981). "Deuterium tagged articles such as explosives and method for detection thereof". U.S. Patent No. 4,251,726. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, Luis W., and Schwemin, Arnold J. (February 23, 1982). "Stabilized zoom binocular". U.S. Patent No. 4,316,649 . Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, Luis W. (February 23, 1982). "Stand alone collision avoidance system". U.S. Patent No. 4,317,119. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, Luis W., (August 16, 1983). "Television viewer". U.S. Patent No. 4,399,455. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, Luis W., and Schwemin, Arnold J. (November 29, 1983). "Stabilized zoom binocular". U.S. Patent No. 4,417,788. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, Luis W., and Schwemin, Arnold J. (October 7, 1986). "Optically stabilized camera lens system". U.S. Patent No. 4,615,590. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, Luis W. (July 12, 1988). "Nitrogen detection". U.S. Patent No. 4,756,866. Washington, DC: U.S. Patent and Trademark Office.
^Alvarez, Luis W., and Sporer, Stephen F. (March 27, 1990). "Inertial pendulum optical stabilizer". U.S. Patent No. 4,911,541. Washington, DC: U.S. Patent and Trademark Office.
Garwin, Richard L., 1992, "Memorial Tribute For Luis W. Alvarez" inMemorial Tributes, National Academy of Engineering, Vol. 5. Washington, D.C.: National Academy Press.
