When in 1931 Paul Dirac concluded from his equation for the electron that there should exist an antiparticle with opposite electric charge, he felt very embarrassed. Such a particle had not yet been discovered, and he really did not want to disturb the scientific community with such a revolutionary proposition. ‘Maybe this strange positively charged particle is simply the proton,’ he suggested. When shortly after that the real antiparticle of the electron (the positron) was identified, he was so surprised that he exclaimed: ‘My equation is smarter than its inventor!’

Nowadays, physicists no longer suffer from such modesty. High energy physicists are now accused of arrogance, and not fully without reason: when the new gauge theory for the weak force became popular, Weinberg and Salam had no trouble at all advertising it as a ‘unification’ of the weak force with the electromagnetic force; and to avoid any misunderstanding: ‘the most important unification since Sir James Clerk Maxwell unified electricity with magnetism’.

I have always maintained that the Weinberg-Salam model does not fully deserve such laudable comment. Did the new theory not start off with two different gauge fields, which we indicate by the mathematical terms ‘SU(2)’ and ‘U(l)’? That is not unification. On the other hand, however, you could emphasize that both force systems are based on exactly the same mathematical principles, and furthermore they are intimately mixed to produce the phenomena that are now explained. And, as in any meaningful theory, numerous new predictions emerged that could be vindicated by experiment. It was much less the case with the previous formalisms, so in this sense one could talk of unification.

Supersymmetry has beautiful mathematics, and so the professional literature is full of it. As we experienced earlier, for instance when the Yang–Mills theory was proposed, we have a brilliant mathematical scheme, which we do not yet know how to fit into the system of existing laws of Nature. It does not make sense, as yet, but we may hope that it will do some time in the future.

There is another scenario, actually much more appealing to our imagination. We have seen that atoms consist of smaller constituents, the protons, neutrons and electrons. And then we discovered that these constituents, in tum, have a further substructure: they are built from quarks and gluons. Why, as you might already have thought earlier, do not things go on like that? Perhaps these quarks and gluons, and also the electrons and all other particles still called ‘elementary’ in the Standard Model, are in tum built out of yet smaller grains of matter?

You would not be the first to have this idea. I have already reported how Jonathan Swift pictured the world of the small as a carbon copy of the world of larger things. Big fleas carry little fleas on their skins, and so on, ad infinitum. Well, just as biologists would try to explain to you that the kingdom of the fleas has to be looked upon somewhat differently, I must also state that the picture of an infinite repetition of building blocks cannot be correct as such.

Our journey to the very small has now brought us beyond the atoms, which are bulky and fragile objects compared with what we shall be occupied with next: the atomic nucleus and whatever is inside. The electrons, now seen ‘at a great distance’ circling around the nucleus, are themselves also small and extremely robust. I now invite you to have a look inside the nucleus, through the eyes of the scientists before 1970. I consider the years around 1970 as a crucial period, but I am now also choosing the year 1970 bcause this was the time I became acquainted with elementary particle physics myself, as a young graduate student at the State University of Utrecht in the Netherlands.

All the physics that I mentioned earlier (and of course a great deal more) was basic stuff for students of theoretical physics. Also, a lot was known about the structure of the atomic nucleus. The nucleus is built from two species of building blocks: protons and neutrons. The proton (Greek np{πρῶτoς = first) owes its name to the fact that the simplest atomic nucleus, that of hydrogen, consists of just one proton. It carries one positive unit of charge. The neutron resembles the proton as if it were its twin brother: its mass is practically the same, its spin is the same, but the electric charge is absent in a neutron; it is neutral.

And now I can report that implicating black holes in our considerations concerning the ultimate laws of physics means progress. I have now concentrated most of my own research towards this subject, asking myself this: suppose you have a tiny black hole and that you insist that it obey both the laws of quantum mechanics and those of gravity. Then how should one describe its behavior?

The shrewdness of this question is that I am assuming that an entire black hole should behave exactly as if it were an atom or molecule obeying the laws of quantum mechanics. Not everybody agrees with me here – not by any means. Some say that black holes are something altogether different. But what is so different about them? Black holes emit particles just like quite a few species of radioactive atoms do. Then why should they not do this by following the same rules? To put it more strongly, I happen to suspect that they absolutely have to obey such laws if you believe in any kind of ‘law and order’ at the Planck length.

One result of my calculations was a total surprise for me. I hit upon practically the same mathematical expressions as the ones in string theory! The formulae for capture and emission of particles by a black hole look exactly like Veneziano's formula. This is odd, since there is no question of strings.

So I liked the Higgs mechanism. But is it correct? Does it yield a healthy theory? What is and what is not allowed in describing elementary particles, and why?

Various universities in different countries organize courses at an international level, called ‘summer schools’, where in prestigious, yet quiet, recreational resorts experts and students convene to give lectures, and listen to them, and most of all to discuss their research subjects. The most prestigious summer school in my subject was in Les Houches, a winter sport resort near Chamonix, on the slopes of Mont Blanc. Presumably because I was too late in registering there, I was not admitted. But I was admitted at my second choice: Cargése. I went there in 1970.

The Institut des Sciences near Cargése on the island of Corsica was established by the French physicist Maurice Lévy. On a beautiful piece of land with a little beach, a small building had been placed where, from 1960 onwards, summer schools and conferences had been held. The 1970 summer school would be about the strong interactions. Together with Gell-Mann, Levy had constructed a model for the strong interaction. Although it was not expected to represent the complete truth, it had the nice feature that all symmetries of the strong interactions were reproduced in a very interesting way. But, because the forces are so strong, the particles will not even approximately move in straight lines, and that made the usual approximation scheme, called ‘perturbation expansion’, unreliable.

There was a way out! However, it originates in quite a different branch of theoretical physics, to wit the physics of metals at very low temperatures. At very low temperatures, ‘quantum phenomena’ can lead to quite remarkable effects. To describe these effects one uses quantized field theories, exactly the same as the ones employed in elementary particle physics. The physics of elementary particles has nothing to do with the physics of low temperatures, but the mathematics is very very similar!

The ‘field’ in some material that becomes important at low temperatures could be the field describing how atoms there oscillate about their equilibrium points, or else the field that describes electrons in this material. At very low temperatures we have to deal with the ‘quanta’ of these fields. For instance, the ‘phonon’ is the quantum of sound. Its behavior resembles that of the photon, the quantum of light, except that the numbers are very different: phonons travel with the speed of sound, hundreds or perhaps thousands of meters per second; the photon travels with light velocity, which is 300000kilometers/second, nearly one million times faster! The elementary particles we are interested in usually have velocities close to that of light.

One of the more spectacular ‘quantum phenomena’ that can take place in strongly cooled metals is called superconductivity, which is the fact that the resistance of such a material to electrical currents vanishes completely.

One of the triumphs of modern particle physics has been the extent to which Quantum Chromodynamics (QCD) has successfully accounted for the strong interaction processes observed at colliders, most notably the dramatic phenomena of hadronic jet and heavy quark production, and the short-distance parton structure of hadrons.

This book gives a comprehensive overview of the physics of high-energy colliders with special emphasis on the study of QCD. After a general description of the QCD Lagrangian, and the properties of asymptotic freedom and colour confinement which follow from it, the most important applications at high-energy colliders are described in detail. These include the production of jets, heavy quarks, electroweak gauge bosons and Higgs bosons. The various methods of measuring the strong coupling constant are summarized. Many important theoretical results are derived from first principles, and the book will be both a textbook and a valuable source of reference material for all particle physicists.

One of the triumphs of modern particle physics has been the extent to which Quantum Chromodynamics (QCD) has successfully accounted for the strong interaction processes observed at colliders, most notably the dramatic phenomena of hadronic jet and heavy quark production, and the short-distance parton structure of hadrons.

This book gives a comprehensive overview of the physics of high-energy colliders with special emphasis on the study of QCD. After a general description of the QCD Lagrangian, and the properties of asymptotic freedom and colour confinement which follow from it, the most important applications at high-energy colliders are described in detail. These include the production of jets, heavy quarks, electroweak gauge bosons and Higgs bosons. The various methods of measuring the strong coupling constant are summarized. Many important theoretical results are derived from first principles, and the book will be both a textbook and a valuable source of reference material for all particle physicists.

One of the triumphs of modern particle physics has been the extent to which Quantum Chromodynamics (QCD) has successfully accounted for the strong interaction processes observed at colliders, most notably the dramatic phenomena of hadronic jet and heavy quark production, and the short-distance parton structure of hadrons.

This book gives a comprehensive overview of the physics of high-energy colliders with special emphasis on the study of QCD. After a general description of the QCD Lagrangian, and the properties of asymptotic freedom and colour confinement which follow from it, the most important applications at high-energy colliders are described in detail. These include the production of jets, heavy quarks, electroweak gauge bosons and Higgs bosons. The various methods of measuring the strong coupling constant are summarized. Many important theoretical results are derived from first principles, and the book will be both a textbook and a valuable source of reference material for all particle physicists.

One of the triumphs of modern particle physics has been the extent to which Quantum Chromodynamics (QCD) has successfully accounted for the strong interaction processes observed at colliders, most notably the dramatic phenomena of hadronic jet and heavy quark production, and the short-distance parton structure of hadrons.

This book gives a comprehensive overview of the physics of high-energy colliders with special emphasis on the study of QCD. After a general description of the QCD Lagrangian, and the properties of asymptotic freedom and colour confinement which follow from it, the most important applications at high-energy colliders are described in detail. These include the production of jets, heavy quarks, electroweak gauge bosons and Higgs bosons. The various methods of measuring the strong coupling constant are summarized. Many important theoretical results are derived from first principles, and the book will be both a textbook and a valuable source of reference material for all particle physicists.

One of the triumphs of modern particle physics has been the extent to which Quantum Chromodynamics (QCD) has successfully accounted for the strong interaction processes observed at colliders, most notably the dramatic phenomena of hadronic jet and heavy quark production, and the short-distance parton structure of hadrons.

This book gives a comprehensive overview of the physics of high-energy colliders with special emphasis on the study of QCD. After a general description of the QCD Lagrangian, and the properties of asymptotic freedom and colour confinement which follow from it, the most important applications at high-energy colliders are described in detail. These include the production of jets, heavy quarks, electroweak gauge bosons and Higgs bosons. The various methods of measuring the strong coupling constant are summarized. Many important theoretical results are derived from first principles, and the book will be both a textbook and a valuable source of reference material for all particle physicists.

One of the triumphs of modern particle physics has been the extent to which Quantum Chromodynamics (QCD) has successfully accounted for the strong interaction processes observed at colliders, most notably the dramatic phenomena of hadronic jet and heavy quark production, and the short-distance parton structure of hadrons.

This book gives a comprehensive overview of the physics of high-energy colliders with special emphasis on the study of QCD. After a general description of the QCD Lagrangian, and the properties of asymptotic freedom and colour confinement which follow from it, the most important applications at high-energy colliders are described in detail. These include the production of jets, heavy quarks, electroweak gauge bosons and Higgs bosons. The various methods of measuring the strong coupling constant are summarized. Many important theoretical results are derived from first principles, and the book will be both a textbook and a valuable source of reference material for all particle physicists.