Physics 1978 PETER LEONIDOVITCH KAPITZA for his basic inventions and discoveries in the area of low-temperature physics ARNO A PENZIAS and ROBERT W WILSON for their discovery of cosmic microwave background radiation 417 THE NOBEL PRIZE FOR PHYSICS Speech by Professor LAMEK HULTHÉN of the Royal Academy of Sci- ences. Translation from the Swedish text Your Majesties, Your Royal Highnesses, Ladies and Gentlemen, This year’s prize is shared between Peter Leonidovitj Kapitza, Moscow, “for his basic inventions and discoveries in the area of low-temperature physics” and Arno A. Penzias and Robert W. Wilson, Holmdel, New Jersey, USA, “for their discovery of cosmic microwave background radi- ation”. By low temperatures we mean temperatures just above the absolute zero, -273”C, where all heat motion ceases and no gases can exist. It is handy to count degrees from this zero point: “degrees Kelvin” (after the British physicist Lord Kelvin) E.g. 3 K (K = Kelvin) means the same as -270°C. Seventy years ago the Dutch physicist Kamerlingh-Onnes succeeded in liquefying helium, starting a development that revealed many new and unexpected phenomena. In 19 11 he discovered superconductivity in mer- cury: the electric resistance disappeared completely at about 4 K. 1913 Kamerlingh-Onnes received the Nobel prize in physics for his discoveries, and his laboratory in Leiden ranked for many years as the Mekka of low temperature physics, to which also many Swedish scholars went on pilgrim- age. In the late twenties the Leiden workers got a worthy competitor in the young Russian Kapitza, then working with Rutherford in Cambridge, England. His achievements made such an impression that a special insti- tute was created for him: the Royal Society Mond Laboratory (named after the donor Mond), where he stayed until 1934. Foremost among his works from this period stands an ingenious device for liquefying helium in large quantities-a pre-requisite for the great progress made in low temperature physics during the last quarter-century. Back in his native country Kapitza had to build up a new institute from scratch. Nevertheless, in 1938 he surprised the physics community by the discovery of the superfluidity of helium, implying that the internal friction (viscosity) of the fluid disappears below 2.2 K (the so-called lambda-point of helium). The same discovery was made independently by Allen and Misener at the Mond Laboratory. Later Kapitza has pursued these investi- gations in a brilliant way, at the same time guiding and inspiring younger collaborators, among whom we remember the late Lev Landau, recipient of the physics prize 1962 “for his pioneering theories for condensed matter, especially liquid helium”. Among Kapitza’s accomplishments we should also mention the method he developed for producing very strong magnetic fields. Kapitza stands out as one of the greatest experimenters of our time, in his domain the uncontested pioneer, leader and master. We now move from the Institute of Physical Problems, Moscow, to Bell Telephone Laboratories, Holmdel, New Jersey, USA. Here Karl Jansky, in the beginning of the thirties, built a large movable aerial to investigate sources of radio noise and discovered that some of the noise was due to radio waves coming from the Milky Way. This was the beginning of radio astronomy that has taken such an astounding development after the sec- ond World War-as an illustration let me recall the discovery of the pulsars, honoured with the physics prize 1974. In the early 1960ies a station was set up in Holmdel to communicate with the satellites Echo and Telstar. The equipment, including a steerable horn antenna, made it a very sensitive receiver for microwaves, i.e. radio waves of a few cm wavelength. Later radio astronomers Arno Penzias and Robert Wilson got the chance to adapt the instrument for observing radio noise e.g. from the Milky Way. They chose a wave length c. 7 cm where the cosmic contribution was supposed to be insignificant. The task of eliminat- ing various sources of errors and noise turned out to be very difficult and time-consuming, but by and by it became clear that they had found a background radiation, equally strong in all directions, independent of time of the day and the year, so it could not come from the sun or our Galaxy. The strength of the radiation corresponded to what technicians call an antenna temperature of 3 K. Continued investigations have confirmed that this background radiation varies with wave length in the way prescribed by wellknown laws for a space, kept at the temperature 3 K. Our Italian colleagues call it “la luce fredda”-the cold light. But where does the cold light come from? A possible explanation was given by Princeton physicists Dicke, Peebles, Roll and Wilkinson and published together with the report of Penzias and Wilson. It leans on a cosmological theory, developed about 30 years ago by the Russian born physicist George Gamow and his collaborators Alpher and Herman. Start- ing from the fact that the universe is now expanding uniformly, they concluded that it must have been very compact about 15 billion years ago and ventured to assume that the universe was born in a huge explosion- the “Big Bang”. The temperature must then have been fabulous: 10 billion degrees, perhaps more. At such temperatures lighter chemical elements can be formed from existing elementary particles, and a tremendous amount of radiation of all wave lengths is released. In the ensuing expan- sion of the universe, the temperature of the radiation rapidly goes down. Alpher and Herman estimated that this radiation would still be left with a temperature around 5 K. At that time, however, it was considered out of the question, that such a radiation would ever be possible to observe. For this and other reasons the predictions were forgotten. Have Penzias and Wilson discovered “the cold light from the birth of the universe” ? It is possible-this much is certain that their exceptional perse- verance and skill in the experiments led them to a discovery, after which cosmology is a science, open to verification by experiment and observation. Piotr Kapitsa, Arno Penzias, Robert Wilson, In accordance with our tradition I have given a brief account in Swedish of the achievements, for which you share this year’s Nobel prize in Physics. It is my privilege and pleasure to congratulate you on behalf of the Royal Swedish Academy of Sciences and ask you to receive your prizes from the hands of His Majesty the King! 421 PJOTR LEONIDOVICH KAPITZA Pjotr Leonidovich Kapitza was born in Kronstadt, near Leningrad, on the 9th July 1894, son of Leonid Petrovich Kapitza, military engineer, and Olga Ieronimovna née Stebnitskaia, working in high education and folk- lore research. Kapitza began his scientific career in A.F. Ioffe’s section of the Electro- mechanics Department of the Petrograd Polytechnical Institute, complet- ing his studies in 1918. Here, jointly with N.N. Semenov, he proposed a method for determining the magnetic moment of an atom interacting with an inhomogeneous magnetic field. This method was later used in the celebrated Stern-Gerlach experiments. At the suggestion of A.F. Ioffe in 1921 Kapitza came to the Cavendish Laboratory to work with Rutherford. In 1923 he made the first experi- ment in which a cloud chamber was placed in a strong magnetic field, and observed the bending of alfa-particle paths. In 1924 he developed methods for obtaining very strong magnetic fields and produced fields up to 320 3 kilogauss in a volume of 2 cm . In 1928 he discovered the linear depen- dence of resistivity on magnetic field for various metals placed in very strong magnetic fields. In his last years in Cambridge Kapitza turned to low temperature research. He began with a critical analysis of the methods that existed at the time for obtaining low temperatures and developed a new and original apparatus for the liquefaction of helium based on the adiabatic principle ( 1934). Kapitza was a Clerk Maxwell Student of Cambridge University (1923- 1926), Assistant Director of Magnetic Research at Cavendish Laboratory (1924-1932), Messel Research Professor of the Royal Society (1930- 1934), Director of the Royal Society Mond Laboratory (1930-1934). With R.H. Fowler he was the founder editor of the International Series of Monographs on Physics (Oxford, Clarendon Press). In 1934 he returned to Moscow where he organized the Institute for Physical Problems at which he continued his research on strong magnetic fields, low temperature physics and cryogenics. In 1939 he developed a new method for liquefaction of air with a low- pressure cycle using a special high-efficiency expansion turbine. In low temperature physics, Kapitza began a series of experiments to study the properties of liquid helium that led to discovery of the superfluidity of helium in 1937 and in a series of papers investigated this new state of matter. During the World War II Kapitza was engaged in applied research on 422 Physics 1978 the production and use of oxygen that was produced using his low pres- sure expansion turbines, and organized and headed the Department of Oxygen Industry attached to the USSR Council of Ministers. Late in the 1940’s Kapitza turned his attention to a totally new range of physical problems. He invented high power microwave generators - planotron and nigotron (1950-1955) and discovered a new kind of con- tinuous high pressure plasma discharge with electron temperatures over a million K. Kapitza is director of the Institute for Physical Problems. Since 1957 he is a member of the Presidium of the USSR Academy of Sciences. He was one of the founders of the Moscow Physico-Technical Institute (MFTI), and is now head of the department of low temperature physics and cryogenics of MFTI and chairman of the Coordination Council of this teaching Institute.