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Obituary: Professor Hannes Alfvn

Hannes Olof Gsta Alfvn, theoretical physicist: born Norrkping Sweden 30 May 1908; Professor of Theory of Electricity, Royal Institute of Technology, Stockholm 1940-45, Professor of Electronics 1945-63, Professor of Plasma Physics 1963-73; Professor, University of California, San Diego (part- time) 1967-89; married 1935 Kerstin Erikson (five children); died Stockholm Sweden 2 April 1995.

Hannes Alfvn made his reputation as a physicist and earned his Nobel Prize in 1970 by establishing the overall importance of magnetic fields in space and in astrophysical phenomena. He is important also for his work for Sweden and for addressing wider international scientific issues. In later years he vigorously - but perhaps not wholly successfully - challenged the Big Bang theory of the universe.

Work on the aurora at the turn of the century by K. Birkeland, on terrestrial magnetic storms by Sidney Chapman, and the observation of magnetic fields in sun-spots by G.E. Hale constituted evidence of a role for magnetic fields in space physics. All this Alfvn re- interpreted in his research in the 1940s. He proposed that magnetic phenomena occurred not only in these circumstances but throughout all space and, because much interstellar matter is electrically conducting, the magnetic field, rather than gravity, would determine the motions of space gases.

His seminal book Cosmical Electrodynamics (1950) presented this worked- out hypothesis and offered explanations of a wide range of observed extra- terrestrial phenomena from the aurora to the generation of cosmic rays. While not all these have stood the test of modern space research, space physicists now accept the role of magnetic fields as central to their subject, and there is a large body of observations to support it.

Alfvn's best-known discovery was theoretical: he combined Clerk Maxwell's equations of electromagnetics with those of hydrodynamics and predicted a new class of natural waves - Alfvn waves - which are produced in conducting media embedded in magnetic fields. He published his results in Nature in 1942. Experimental support for his theory was obtained in his Stockholm laboratory by his students Stig Lundquist in 1949 and by Bo Lehnert using liquid metals in 1951, and later Alfvn waves in conducting gases were identified by nuclear fusion researchers in the UK and the US. In this way Alfvn founded the subject which goes by the somewhat cumbersome title ``magnetohydrodynamics'', the science of fluids in magnetic fields.

Alfvn was educated at Uppsala University, and trained at the Nobel Institute of Physics under Manne Siegbahn in Stockholm, at Cambridge under Ernest Rutherford, and under Otto Hahn and Lise Meitner (the researchers of fission) in Berlin. But the call of space physics was stronger than that of nuclear physics, and under his Professorship (1940-67) the Royal Institute of Technology, Stockholm, became a Mecca for the physics of space and of conducting gases.

Alfvn served on Sweden's Atomic Energy Board (1956-68) and as a scientific adviser to the Swedish government (1961-67). His arguments were among those which persuaded public opinion in Sweden that, despite the threatening armaments of the Soviet Union, Sweden's best prospect of independence and security lay in concentrating resources on conventional weapons. His increasingly strong objections to a particular Swedish design for proposed civil nuclear plants, together with the evident connection with nuclear weapons, led to his resignation from the Swedish Atomic Energy Board. Thereafter Alfvn divided his time between the University of California, San Diego and the Royal Institute of Technology of Stockholm. He retired to Sweden in 1989.

During these later years the problem of the formation of the solar system, of the structure of galaxies and the origin of the universe all attracted his attention. With Gustaf Arrhenius he wrote an important monograph on the evolution of the solar system. With the aid of an idea of Klein, namely that the universe was originally created out of nearly equal amounts of matter and anti-matter, he proposed his refreshing alternative to the Big Bang history of the universe.

Alfvn was an international figure: he was the first Western scientist to penetrate into the Soviet Union's atomic energy institutes; and he came to Harwell in the 1950s taking an intense interest in nuclear fusion research, where magnetic fields and conducting gases are the key ingredients. Indeed the UK's first attempt to find Alfvn waves was made in the Zeta nuclear fusion apparatus at Harwell.

He was a member, and then President (1970-75), of Pugwash International Conferences on Science and World Affairs (founded by Bertrand Russell among others). Under his presidency, Pugwash's interests expanded from the prevention of global thermonuclear war to wider issues of human conflict, such as population pressures and new, alternative energy sources to nuclear energy.