Hannes Alfvén

Swedish physicist

• Born: May 30, 1908
• Birthplace: Norrköping, Sweden
• Died: April 2, 1995
• Place of death: Djursholm, Sweden

Alfvén developed magnetohydrodynamics, a branch of physics that studies the propagation of currents and electromagnetic waves through fluids, and studied its applications to plasmas, leading to his description of the physics of the aurora, radiation belts around planets having magnetic fields, and other astrophysical phenomena.

Early Life

Hannes Alfvén (HAHN-nehs ahl-VAYN) was born in Norrköping, Sweden. His parents, Johannes Alfvén and Anna-Clara Romanus, were both medical doctors. His mother was one of the first female doctors in Sweden, and his father showed an interest in science beyond medicine. Hugo Alfvén, one of his uncles, was a well-known musical composer. Another uncle was an inventor, and a third uncle was interested in astronomy. As a child, Alfvén was given a book on astronomy, which sparked his lifelong interest. He was a member of the radio club in high school, and he built a radio receiver. However, his hometown had no radio station. Stockholm, which did have a radio station, was too far away from Norrköping for its signal to be heard. With much effort, Alfvén was able to hear a station located in Aberdeen, Scotland. With this success, he became interested in electrical engineering.

In 1926, Alfvén entered Uppsala University, where he studied electrical engineering and physics. He was awarded a doctorate in 1934 after submitting his doctoral thesis, “Investigations of the Ultra-short Electromagnetic Waves.” Alfvén later said that his doctoral research was a continuation of the activities he participated in with the radio club in high school.

Life’s Work

Alfvén was appointed a lecturer in physics at Uppsala University in 1934, where he combined his interests in electricity and astronomy. The high energies achieved by “cosmic rays,” ions that move through space at speeds close to that of light and that continuously hit the earth’s atmosphere, puzzled astrophysicists. Alfvén became interested in the physical mechanisms that could accelerate charged particles in space to such high energies. He was particularly critical of earlier work on this topic, believing that researchers presented ideas that were not constrained by the results of the most recent experiments.

Alfvén was convinced that the origin of the cosmic rays could be explained simply by applying “kinetic gas theory,” an approach that was successfully applied to explain the macroscopic properties of gases, such as pressure, temperature, or volume, by considering their microscopic properties of composition and motion, to the conditions that are found in space. Alfvén proposed a mechanism for the acceleration of cosmic rays based on the presence of electromagnetic fields in space. A version of that mechanism, expanded upon by Enrico Fermi and now known as the Fermi mechanism, remains the favored mechanism to explain cosmic ray acceleration.

In 1937, Alfvén was appointed a research physicist at the prestigious Nobel Institute for Physics in Stockholm. He devoted much of his career to making scientists aware of the importance of electric fields and electric currents in space. His work on cosmic ray acceleration led him to propose the existence of a galactic magnetic field. At that time, interstellar space was believed to be a vacuum, so the accepted view was that there could be no significant magnetic field in space because the magnetic fields of the stars were too weak to reach that far. Alfvén suggested that “plasma,” a gas of positively charged ions, could, in interstellar space, conduct electric currents strong enough to produce a significant magnetic field. This galactic magnetic field was finally discovered many years after Alfvén first proposed it.

In 1940, Alfvén was appointed professor in the theory of electricity at the Royal Institute of Technology, also in Stockholm. It was here that he did the research that brought him the most recognition. Electromagnetic waves were known not to penetrate more than a few wavelengths into solid conductors. However, in 1942, Alfvén published calculations showing that low-frequency electromagnetic waves, now called Alfvén waves, should propagate through the interior of fluids, such as plasmas.

Alfvén frequently set out to solve a particular problem but was able to generalize the results to be more broadly applicable. He was investigating the mechanism for the production of “sunspots,” magnetic disturbances on the sun that appear darker than the surrounding area, when he discovered what came to be called Alfvén waves. While trying to model magnetic disturbances of the sun, Alfvén recognized that electric currents in the solar plasma would result in wave motion. At that time electromagnetic theory and fluid motion theory were separate fields of physics, but Alfvén’s work combined them into a new field called “magnetohydrodynamics.” It was not until 1949 that Alfvén waves were first detected. Stig Lundquist, a physicist working in Alfvén’s laboratory, produced them in liquid mercury.

The importance of Alfvén’s work was not immediately recognized by the scientific community. It was difficult to test Alfvén’s theories because plasmas were thought to occur only rarely under natural conditions, typically in lightning strikes. With the development of nuclear weapons and efforts to develop nuclear fusion as an energy source, plasmas were routinely being generated by the 1950’s, and magnetohydrodynamics became an important field of study. In addition, Alfvén proposed that plasmas should occur in the atmosphere of the earth and in a variety of locations in space. He spent much of his professional career investigating the occurrence of plasmas in space, and discussing their significance. Alfvén was awarded the 1970 Nobel Prize in Physics for his work on magnetohydrodynamics.

Two decades before the Explorer I satellite discovered Earth’s Van Allen radiation belt, a ring of charged particles that surrounds the earth, Alfvén gave an intuitive explanation of how energetic charged particles can orbit around a magnetized planet. Before Alfvén developed his method of calculating the path a charged particle follows in a magnetic field, particle paths had to be calculated by a tedious and time-consuming numerical integration technique. Alfvén separated the motion into two components, one describing the gyration of the particle perpendicular to the local magnetic field and the second describing the drift of the center of motion. Using this technique, Alfvén noted that a ring of charged particles would be stable around a planet with a magnetic field. However, he failed to take the next step of recognizing that such a ring of charged particles could exist around the earth. That step was taken by Fred Singer, in 1956, after hearing a lecture by Alfvén.

Alfvén regarded himself as a generalist, who investigated a variety of phenomena that involved plasmas and their effects in a variety of contexts, while many other physicists concentrated their efforts on one field of research. Thus, he was sometimes regarded as an interloper, trying to explain a phenomenon that other researchers thought to be outside his area of expertise. When he developed his model of “aurora,” a luminous atmospheric phenomenon appearing as bands of light in the night sky, the model was initially rejected by the leading atmospheric physicists, and Alfvén could not publish his results in any of the leading scientific journals. Finally, he published his model, now the accepted explanation for aurora, in an obscure journal.

In 1950 Alfvén, working with Nicolai Herlofson, proposed the mechanism for emission of “synchrotron radiation” light emitted when high-speed electrons spiral through magnetic fields by astronomical objects. This radiation was discovered in 1956 by Geoffrey Burbidge.

As Alfvén’s research interests evolved, his title at the Royal Institute of Technology was changed to professor of electronics in 1945 and to professor of plasma physics in 1963. In 1967, Alfvén was appointed a professor of physics at the University of California, San Diego. He divided his time between California, where he worked from fall until spring, and Sweden, where he worked from spring until fall.

Later in life, Alfvén became interested in humankind’s ultimate fate, and he explored issues such as population growth, the environment, and disarmament. He and his wife, Kerstin, cowrote Living on the Third Planet (1972), which explored their views on these issues. Alfvén retired in 1991 and lived in Sweden until his death, at the age of eighty-six, in 1995.

Significance

Alfvén made significant contributions to understanding the physics of plasmas, including theories describing the behavior of aurora in Earth’s atmosphere, Van Allen radiation belts, the effect of solar magnetic storms on the earth’s magnetic field, the earth’s magnetosphere, and the dynamics of plasmas in the Milky Way galaxy. Many of Alfvén’s ideas were ahead of their time. He predicted phenomena well before they were discovered, leading, oftentimes, to his work being forgotten by the time the phenomenon he predicted was observed.

Later in his life, Alfvén used the prestige he gained from the Nobel Prize to influence national and international policy. He joined the Pugwash movement, a group of influential scholars who sought to reduce the danger of armed confrontation in the nuclear era. He also became concerned with the lack of planning for the disposal of radioactive waste from nuclear power reactors, and he was influential in the debate that resulted in restrictions on the use of nuclear power in Sweden.

Bibliography

Alfvén, Hannes. “Memoirs of a Dissident Scientist.” American Scientist, May-June 1988, 249-251. A first-hand account of Alfvén’s scientific achievements and his efforts to have his ideas accepted by the scientific community.

Dardo, Mauro. Nobel Laureates and Twentieth-Century Physics. New York: Cambridge University Press, 2004. Chronicles major developments in physics since 1901, the year the first Nobel Prize in Physics was awarded. Includes discussion of the work of prize winners.

Falthammar, Carl-Gunne, and Alexander J. Dessler. “Hannes Alfvén.” Proceedings of the American Philosophical Society 150, no. 4 (2006): 649-662. An extensive biography of Alfvén, explaining how he developed interests in physics and astronomy, describing his successes, failures, and his difficulty in getting his revolutionary ideas accepted by the scientific community.

‗‗‗‗‗‗‗. “The Life and Times of a Premier Space Physicist.” Earth in Space 9, no. 5 (January, 1996). An account of Alfvén’s scientific accomplishments, focusing on his achievements in atmospheric and space science.