Presentation Speech by Professor Lamek Hulthén of the Royal Academy of Sciences

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 radiation”.

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 1911 he discovered superconductivity in mercury: 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 pilgrimage.

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 institute 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 investigations 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 second 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 eliminating 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. Starting 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 explosionthe “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 expansion 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 perseverance 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!