Presentation Speech by Professor Bengt Nagel of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen,

This year’s Nobel prize in Physics is shared equally between Sheldon Glashow, Abdus Salam and Steven Weinberg “for their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles, including inter alia the prediction of the weak neutral current”.

Important advances in physics often consist in relating apparently unconnected phenomena to a common cause. A classical example is Newton’s introduction of the gravitational force to explain the fall of the apple and the motion of the moon around the earth. – In the 19th century it was found that electricity and magnetism are really two aspects of one and the same force, the electromagnetic interaction between charges. Electromagnetism, with the electron playing the leading part and the photon – the electromagnetic quantum of light – as the swift messenger, dominates technology and our everyday life: not only electrotechnics and electronics, but also atomic and molecular physics and hence chemical and biological processes are governed by this force.

When one began to study the atomic nucleus in the first decades of our century, two new forces were discovered: the strong and the weak nuclear forces. Unlike gravitation and electromagnetism these forces act only over distances of the order of nuclear diameters or less. The strong force keeps the nucleus together, whereas the weak force is responsible for the so called beta decays of the nucleus. Most radioactive substances used in medicine and technology are beta radioactive. The electron also participates in the weak interaction, but the principal part is played by the neutrino, a particle which is described as follows in a poem by the American writer John Updike:

“Cosmic Gall”

Neutrinos, they are very small.
They have no charge and have no mass
And do not interact at all.
The earth is just a silly ball
To them, through which they simply pass,
Like dustmaids down a drafty hall
Or photons through a sheet of glass.
– – –
At night, they enter at Nepal
And pierce the lover and his lass
From underneath the bed – you call
It wonderful; I call it crass.

The description is accurate, apart from the statement ‘they do not interact at all’; they do interact through the weak force. The neutrinos of the poem, entering the earth at night at Nepal and exiting in the U.S. in a sort of reversed China syndrome, come to us from the centre of the sun. Solar energy, necessary for life on earth, is created when hydrogen is burnt to helium in the interior of the sun in a chain of nuclear reactions – even the advocates of “Solsverige” must ultimately rely on nuclear energy although it must be said that the fusion reactor Sun is well encapsuled and sufficiently relocated away from populated areas. The first ignating and moderating link in this chain, burning hydrogen to deuterium, is based on the weak force, which could then be called the Sunignator and Suntamer.

The theory which is awarded this year’s prize, and which was developed in separate works by the prizewinners in the 60’s, has extended and deepened our understanding of the weak force by displaying a close relationship to the electromagnetic force: these two forces emerge as different aspects of a unified electroweak interaction. This means e.g. that the electron and the neutrino belong to the same family of particles; the neutrino is the electron’s little brother. Another consequence of the unified theory is that there should exist a new kind of weak interaction. It was formerly assumed that weak processes could occur only in connection with a change of identity of the electron to neutrino (or vice versa); such a process is said to proceed by a charged current, since the particle changes its charge. The theory implies that there should also be processes connected with a neutral current in which the neutrino – or else the electron – acts without changing identity. Experiments in the 70’s have fully confirmed these predictions of the theory.

The importance of the new theory is first of all intrascientific. The theory has set a pattern for the description also of the strong nuclear force and for efforts to integrate further the interactions between elementary particles.

Let me end by giving an example of the intricate links which exist between different branches of natural science.

Our body is to a large part constructed from “stardust”: the elements besides hydrogen which build our cells have been formed in the interior of stars in nuclear reactions, which form a continuation of the processes taking place in our sun. According to the astrophysicists, certain heavy elements appearing in life-important enzymes and hormones – iodine and selenium are examples of such elements – can probably only be created in connection with violent explosions of giant stars, so called supernova explosions, which occur in our Galaxy once every one or two hundred years. It is likely that neutrinos interacting via the neutral current play an important role in these explosions, in which a large part of the matter of the star is thrown out into space. Thus, for our functioning as biological beings we rely on elements formed milliards of years ago in supernova explosions, with the new kind of weak force predicted by the theory contributing in an important way; really a fascinating connection between biology, astrophysics and elementary particle physics.

Professors Sheldon Glashow, Abdus Salam, and Steven Weinberg,

In my talk I have tried to give a background to your great discoveries in the borderland between a strange but known country and the probably large unknown territory of the innermost structure of matter.

Our way of looking at this structure has changed radically in the last decade. The theory of electroweak interaction has been one of the most important forces to bring about this change of outlook.

It is a privilege and a pleasure for me to convey to you the warmest felicitations of the Royal Swedish Academy of Sciences and to invite you to receive your prizes from the hands of his Majesty the King.