Carl David Anderson

Physicist

• Born: September 3, 1905
• Birthplace: New York, New York
• Died: January 11, 1991
• Place of death: San Marino, California

American physicist

At the age of thirty-one, American physicist C. D. Anderson was the second youngest person ever awarded a Nobel Prize. He received the honor for his discovery of the positron, a particle that helped explain the nature of matter and antimatter. Anderson’s discovery was instrumental in founding the field of particle physics, which has unlocked many of the mysteries of the universe.

Born: September 3, 1905; New York, New York

Died: January 11, 1991; San Marino, California

Also known as: C. D. Anderson; Carl David Anderson Jr.

Primary field: Physics

Specialties: Atomic and molecular physics; quantum mechanics

Early Life

Carl David Anderson was born in September of 1905 in New York City, the only child of Swedish immigrants Emma Adolfina Ajaxson and Carl David Anderson. In 1912, the Andersons left New York for Los Angeles, settling near the still-developing Throop University. By the time Anderson was ready to enroll in college, Throop University had become the California Institute of Technology (Caltech), run by Nobel laureate Robert A. Millikan. Anderson began his studies at Caltech in 1923, first pursuing electrical engineering, but later becoming interested in physics because of the influence of Professor Ike Bowen.

Anderson was an impressive and ambitious student, displaying a particular interest in X-rays. In 1927, Anderson earned his bachelor’s degree in physics engineering (now called applied physics); he received a PhD in the same discipline three years later. Anderson’s doctoral paper, about electron distribution in X-ray-inundated gases, was published in the journal Physical Review in 1930.

Anderson hoped to continue his research with electrons and radiation by studying gamma rays. Millikan advised Anderson to apply for a National Research Council fellowship, which would have allowed him to conduct research at a number of prestigious schools. However, Millikan eventually decided that he wanted Anderson’s help with studying cosmic radiation (radiation emanating from space), which was still a mystery to scientists.

The arrangement with Millikan was expected to last for about a year, after which Anderson would move on to study and conduct research at other schools. It soon became clear, however, that the relationship was permanent. By 1939, Anderson had become a full professor at Caltech, and would remain there for the rest of his professional career.

Life’s Work

At his mentor’s request, Anderson stayed at Caltech in 1930 to assist Millikan with his observations of cosmic rays. Anderson was planning to observe secondary electrons, those generated by radiation. His observations, however, showed that some particles that appeared to be electrons had a positive charge, as opposed to the negative charge electrons carry. Anderson was able to isolate and study these mysterious particles. Their tracks in a particle detector called a cloud chamber indicated a mass approximately equal to that of electrons, which are much smaller than protons. It seemed to Anderson that he had discovered an entirely new particle. He published his findings as “Energies and Cosmic-Ray Particles” in the August 1932 issue of Physical Review.

English physicist Paul Dirac had proposed the existence of such a particle three years earlier, theorizing that electrons could absorb energy in cosmic radiation to become positively charged. Anderson was the first to see evidence of this strange phenomenon, however. The particle, which Anderson called a positron, was indeed a positively-charged electron. Anderson’s discovery of the positron was the first evidence indicating the existence of antiparticles, the components of antimatter.

Everything in the observable universe is matter, and all matter is made up of particles. But cosmic rays like those studied by Anderson often contain antiparticles. Modern physicists have now confirmed that every known particle has an antiparticle, identical in almost every way, but with an opposite charge. Antimatter can only exist in very small quantities and for very short periods of time and in very specific conditions, because contact between matter and antimatter causes both the particles and antiparticles to be destroyed and converted into other types of particles.

Though Anderson was familiar with Dirac’s theory, and understood that it described a methodology for discovering positrons, he maintained that the discovery was nothing more than a happy accident. Building on this idea, Anderson took his cloud chamber to as many places as he could to see what other types of particles existed. At great personal expense, he and his assistant, Seth Neddermeyer, drove a truck with a cloud chamber in the back to the top of Pike’s Peak in Colorado. During this excursion, he discovered a particle he initially called a mesotron, then a mu meson, before it was finally dubbed a muon. This particle, which had a negative charge and a mass in between that of an electron and a proton, appeared to be one that had been proposed years earlier by Japanese physicist Hideki Yukawa, but turned out to be produced when Yukawa’s proposed particle (later identified and dubbed a pi meson or pion) decayed.

The trip proved fruitful, and Anderson’s extraordinary accomplishments—in particular his discovery of the positron—earned him the Nobel Prize in Physics in 1936. After receiving the Nobel Prize, Anderson became a reluctant celebrity. He was elected to the National Academy of Sciences in 1938, where he later served chairman of the Physics Section. For Anderson, this attention was generally unwelcome, as he had little interest in becoming a public figure.

In 1935, Anderson received the Gold Medal of the American Institute of the City of New York, followed by the Elliott Cresson Medal of the Franklin Institute in 1937, the Presidential Certificate of Merit in 1945, and the John Ericsson Medal of the American Society of Swedish Engineers in 1960. In addition to these awards, Anderson also received honorary degrees from Colgate University, Temple University, and Gustavus Adolphus College.

Anderson was not particularly interested in politics or government, though he did contribute to the National Defense Research Committee and the Office of Scientific Research and Development during World War II. He also worked with other Caltech scientists on the Caltech artillery rocket project, which sought to increase the accuracy and effectiveness of naval rockets.

After the turmoil of the war and his work on time-consuming projects eased, Anderson married Lorraine Bergman in 1946. Shortly afterward, his relationship with the Navy aided his work with cosmic rays, when he was granted permission to install cloud chambers in two B-29 heavy bombers to study the decay of cosmic radiation. As the technology for studying cosmic rays improved, however, Anderson was left behind due to Caltech’s resistance to new, larger machinery. Other universities began building particle accelerators, allowing other scientists to surpass Anderson’s research capabilities.

In 1962, Anderson was invited along with other Nobel laureates to a formal White House dinner with President John F. Kennedy. It was during this dinner that Kennedy made his famous remark that so much talent had not been present at a White House dinner since Thomas Jefferson had dined alone.

Anderson retired from teaching in 1970, after having spent his entire career at Caltech. He was appointed to the Board of Trustees as professor emeritus in 1976, but spent much of his time pursuing his hobbies of ham radio, tennis, and mountain climbing. Anderson died on January 11, 1991, in San Marino, California.

Impact

The entire field of high-energy or particle physics may be considered to have started with Anderson’s discovery of the positron. His discovery gave physicists a clearer understanding of elementary particles. Furthermore, this branch of physics has led to the unveiling of a very complex set of particles and of new forces that operate in the subnuclear realm. Yukawa and Dirac, among others, had opened the door to the field with their postulation of the existence of new particles, and Anderson confirmed what they had theorized.

Bibliography

Anderson, Carl D. The Discovery of Anti-Matter: The Autobiography of Carl David Anderson, the Youngest Man to Win the Nobel Prize. Ed. Richard J. Weiss. London: World Scientific, 1999. Print. Includes chapters on the discovery of positrons, antimatter, muons, and Anderson’s winning the Nobel Prize.

---. The Production and Properties of Positrons. Stockholm: Impr. Royale, 1936. Print. Anderson’s Nobel lecture. Includes images of positron trails.

Carlson, Per. “A Century of Cosmic Rays.” Physics Today 65.2 (2012): 30. Print. Discusses cosmic ray research over the past hundred years, with coverage of Anderson and the 1936 Nobel Prize in Physics.