Alfven, Hannes Olof Gosta (physicist)


(1908-1995) Swedish Plasma Physicist, Astrophysicist

Hannes Alfven was the founder of the modern field of plasma physics, the study of electrically conducting gases, and the father of the branch of plasma physics known as magnetohydrodynam-ics (MHD), the study of plasmas in magnetic fields. He was honored for this work with the 1970 Nobel Prize in physics.

Alfven was born on May 30, 1908, in Norrkoping, Sweden, to Anna-Clara Romanus and Johannes Alfven, both physicians. He attended the University of Uppsala and earned a Ph.D. in 1934 for a dissertation on ultrashort electromagnetic waves; in that year, he was appointed lecturer in physics at Uppsala. In 1935, he married Kerstin Maria Erikson, with whom he would share a 67-year marriage that would produce five children.

He became a research physicist, in 1937, at the Nobel Institute in Stockholm, where he began his groundbreaking work in plasma physics. Plasmas are highly ionized gases containing both free positive ions and free electrons. The dominant state of matter in the universe, they are rare on Earth, but abundant in stars, galaxies, and intergalactic space. Alfven studied plasma physics primarily within the context of astrophysics, beginning with an attempt to explain the phenomenon of sunspots by investigating the interaction of electrical and magnetic fields with plasmas. He formulated the frozen-influx theorem, which postulates that under certain conditions, a plasma is bound to the magnetic lines of flux passing through it. On the basis of this theorem he then postulated the existence of the galactic magnetic field, which now forms the basis for cosmic magnetism, using the idea to explain the origin of cosmic rays.

In the early 1930s, most physicists believed that cosmic rays were gamma rays that permeated the whole universe. But when cosmic rays were discovered to be charged particles, Alfven made a unique proposal: if the galaxy contained a large-scale magnetic field, then cosmic rays could move in spiral orbits within the galaxy, because of the forces exerted by the magnetic field. He argued that there could be a magnetic field pervading the entire galaxy if plasma were spread throughout the galaxy. This plasma could carry the electrical currents that would then create the galactic magnetic field. Whereas this intuitive hypothesis was first dismissed on the grounds that interstellar space was known to be a vacuum incapable of supporting electrical currents and particle beams, it was later accepted by physicists and became very fashionable in the 1980s and 1990s.

Alfven was the first to devise the guiding center approximation, a widely used technique that enables the complex spiral movement of a charged particle in a magnetic field to be calculated with relative ease. In 1939, using this technique, Alfven proposed a theory to explain auroras and magnetic storms that would exert a profound influence on future attempts by physicists to understand the Earth’s magnetosphere. At the time, the renowned space scientist Sydney Chapman argued that the currents involved were restricted to flow only in the ionosphere with no downflowing currents. Alfven challenged this widely accepted theory by championing the ideas of the Norwegian scientist Kristian Birkeland, who believed that electric currents flowing down along the Earth’s magnetic fields into the atmosphere were the cause of the aurora and polar magnetic disturbances. Alfven won the debate decades later, in 1974, when Earth satellites were able to measure and observe the downflowing currents for the first time. In a similar manner many of Alfven’s theories about the solar system were disputed for many years and only vindicated as late as the 1980s, through measurements of cometary and planetary magnetospheres by artificial satellites and space probes.

In 1940, Alfven joined the Royal Institute of Technology, Stockholm, and became professor of electronics at the Royal Institute in 1945. In 1942, he hypothesized that a form of electromagnetic plasma wave (now called the Alfven wave) could propagate through plasma, a phenomenon that was, in fact, later observed by other physicists in plasmas and in liquid metals. On purely physical grounds he concluded that an electromagnetic wave could propagate through a highly conducting medium such as the ionized gas of the Sun, or in plasmas anywhere. Since his hypothesis contradicted james clerk maxwell’s theory of electromagnetism, initially no one took it seriously. It was, after all, “well known” that electromagnetic waves could penetrate only a very short distance into a conductor and that as the resistance of a conductor became smaller and smaller, the depth of penetration of an electromagnetic wave would approach zero. Thus, with an ideal electrical conductor, there could be no penetration of electromagnetic radiation. Alfven’s proposal of a form of electromagnetic wave that could propagate in a perfect conductor with no attenuation or reflection was ignored. However, in 1948, when Alfven lectured on it at the University of Chicago, enrico fermi agreed with the conclusions of Alfven’s work and it became widely accepted.

Also in 1942 Alfven put forth a theory of the origin of the planets in the solar system, sometimes called the Alfven theory, which hypothesizes that planets were formed from the material captured by the Sun from an interstellar cloud of gas and dust. The theory envisages the following series of events: As atoms were drawn toward the Sun, they became ionized and influenced by the Sun’s magnetic field. Then, in the plane of the solar equator, the ions condensed into small particles, which, in turn, coalesced to form the planets. Although Alfven’s theory did not adequately explain the formation of the inner planets, it was important in suggesting the role of MHD in the origin of the solar system.

In 1950, together with his colleague N. Herlofson, Alfven was the first to identify non-thermal radiation from astronomical sources as synchrotron radiation, which is produced by fast-moving electrons in the presence of magnetic fields. The recognition that the synchrotron mechanism of radiation is important in celestial objects proved extremely productive in astrophysics, since nearly all the radiation recorded by radio telescopes derives from this mechanism.

It was in the 1960s that Alfven formulated his opposition to the big bang theory of cosmology. He wrote, “I have never thought that you could obtain the extremely clumpy, heterogeneous universe we have today, strongly affected by plasma processes, from the smooth, homogeneous one of the Big Bang, dominated by gravitation.”

Instead of the big bang theory, in which the universe is created out of nothing, in a fiery explosion, at a fixed moment in time, he postulated the plasma universe, an evolving universe without beginning or end. He believed that the appeal of the big bang was rooted in its mythological approach, in which a perfect principle is sought, on the basis of which “the gods” created the universe. He juxtaposed to this, what he called a scientific, empirical approach, reasoning that, since we never observe something emerging from nothing, there is no reason to assume that this occurred in the distant past. On the other hand, since we now see an evolving universe, plasma cosmology assumes that the universe has always existed and evolved and will continue to do so for an infinite time to come. Today big bang theory continues to be more persuasive to the great majority of physicists, in large part as a result of the observation of the cosmic background radiation that permeates the universe, believed to be a remnant of the initial explosion. However, Alfven’s theory continues to attract a small dissident minority.

Around this time, in addition to his scientific debates, Alfven became embroiled in political controversies. He was a writer of popular science books, sometimes with the collaboration of his wife, Kerstin Maria Erikson Alfven, and in 1966 he published, under the pseudonym Olaf Johannesson, The Great Computer, a pointed political-scientific satire in which the planet is taken over by computers. In Alfven’s hands, this popular science fiction theme became a vehicle for ridiculing the growing infatuation of government and business with computers, as well as for attacking a large part of the Swedish scientific establishment.By the following year, Alfven’s quarrel with the Swedish government, particularly his condemnation of Sweden’s nuclear research program for allocating insufficient funds for projects on peaceful uses of thermonuclear energy, became bitter enough for him to decide to leave Sweden. He was immediately offered two positions—one in the United States and the other in the Soviet Union. After two months in the Soviet Union, he became a professor at the University of California, San Diego. Eventually, he reconciled his differences with the Swedish scientific bureaucracy and divided his time between the Royal Institute and the University of California.

In 1970, he shared the Nobel Prize with Louis-Eugene-Felix Neel. He was president of the Pugwash Conference on Science and World Affairs and became a leading advocate of arms control.

In spite of such recognition, for much of his career his ideas were dismissed or treated with condescension, forcing him to publish in obscure journals.

Alfven’s contentious career was balanced by his private life—his happy marriage and large, accomplished family; his zest for travel; and his physical vitality. He died on April 2, 1995, in Stockholm, at the age of 86.

Alfven was a controversial figure, regarded by a few as “the Galileo of the late 20th century” and by many as a heretic for his rejection of the big bang theory. Yet his contributions to physics are many and undeniable and are today being applied in the development of particle beam accelerators, controlled thermonuclear fusion, rocket propulsion, and the braking of reentering space vehicles. Applications of his research in space science include explanations of the Van Allen radiation belt, the reduction of the Earth’s magnetic field during magnetic storms, the magnetosphere (a protective plasma envelope surrounding the Earth), the formation of comet tails, the formation of the solar system, the dynamics of plasmas in our galaxy, and the fundamental nature of the universe itself. His numerous contributions to this field are reflected in the concepts that bear his name, including the Alfven wave, Alfven speed, and Alfven limit.

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