Presentation Speech by Professor Professor Lars Brink, Member of the Royal Swedish Academy of Sciences; Chairman of the Nobel Committee for Physics, 10 December 2013

Professor Lars Brink delivering the Presentation Speech for the 2013 Nobel Prize in Physics at the Stockholm Concert Hall. Copyright © Nobel Media AB 2013
Photo: Alex Ljungdahl

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen,

“The world is so big so big …
Bigger than you can ever imagine …”

Since Zacharias Topelius wrote those words almost 150 years ago, we have understood that the world is even bigger and more complex than people could imagine at that time. We can now explore space billions of light-years away, and with the biggest microscopes, particle accelerators, we can study physics at incredibly small distances. Is it then not presumptuous of us to try to understand all the physics that the world holds, to try to find laws that cover a multitude, perhaps all of those phenomena. No! Albert Einstein once wrote that the most fantastic about Nature is that it is possible to comprehend.

Edith Södergran once wrote: “Can you catch in your hands a star that is rising towards the zenith, can you measure its flight?”

Yes we can measure its flight. Isaac Newton explained to us that the law we should use for the movement of a star is the same as the one that governs an apple falling on Earth. A law of physics describes many phenomena that seem to have completely different origin. What do the stars and the apple have in common? Well, they have a mass and the force of gravity is determined by the masses of the objects, nothing else. Nature is rational.

When the new quantum physics was developed a hundred years ago, we also understood that Nature is quantised. Matter can be divided into its smallest constituents. Exactly one hundred years ago Niels Bohr explained that the hydrogen atom consists of a small nucleus, a single proton, with an electron circling around it. We could then understand that the unified theory for the world must be sought for in the Microcosm.

The large particle accelerators developed since the 1950s are the tools we use to survey the Microcosm.  The complexity of these modern constructions corresponds to that of the large cathedrals built one thousand years ago. We have found not only a multitude of new particles but also two forces that are only apparent in the Microcosm; the Strong Nuclear Force that binds the nuclei and the Weak Force responsible for radioactive decay. How can we describe such forces that only act over very small distances? The rules of the game are very restrictive.

The prototype of a successful theory was quantum electrodynamics, which describes a force with long range. Just think of two charged balls. If we simply change the force from long range to short range the result is inconsistent because important symmetries of the theory are destroyed.  However, it turns out that there is a way to make the force short range and still keep such symmetries in the equations of the theory by choosing a ground state that breaks the symmetry.

Could that be used? It required the existence of a new massless particle together with a massive one. The massless particle would lead to a new type of radiation that has never been seen. Could one get rid of this by modifying the theory or were scientists on the wrong path?

The solution came almost fifty years ago in two papers, one by François Englert and Robert Brout and the other by Peter Higgs – two short papers roughly a page long, that changed the world. They simply combined a theory like electromagnetism with the two fields which lead to the two particles just mentioned, and showed that the unwanted massless particle, which would lead to unobserved radiation, combined with the electromagnetic field to produce a short range force. However the new massive particle still appeared in the theory. We now had a theory analogous to electromagnetism, but with short range forces and massive particles.   We had unified the Electromagnetic and the Weak forces. What did particle physicists do now? They ignored the new theory! Could it really be consistent? Brout, Englert and Higgs believed so, but it was not until seven years later that a young Dutch student, Gerhard ‘t Hooft indeed could show that the theory works, in a work of immense complexity leading to the Nobel Prize in 1999.

Now the physics world understood, and very quickly developed a unified theory of the forces that act in Microcosm (the strong, electromagnetic and weak forces).  This is called “the Standard Model of Particle Physics”, a theory that in practice governs the world as long as the force of gravity can be ignored. It demanded new particles, quarks and leptons and force particles, which were speedily discovered. But the new particle that Brout, Englert and Higgs had predicted, which was now understood to give masses to all massive fundamental particles was not found. Thirty years ago we had essentially found everything except this particle.  Was it really there?

It was understood that the discovery of such a particle would require a very large accelerator, one that could produce collisions with an energy comparable to that arising in the very early universe. It took some thirty years of preparation and then construction at CERN in Geneva before scientists could search for the wanted particle. In 2010 6,000 scientists began two large experiments, and on July 4, 2012 they spread the news that they had indeed found the particle. The Standard Model was complete and it had been found that Nature follows precisely that law that Brout, Englert and Higgs had created. A fantastic triumph for Science.

Professeur Englert, vous avez, avec votre collègue le Professeur Brout tristement décédé et avec le Professeur Higgs, trouvé la clé pour comprendre la masse des particules élémentaires, découverte pour laquelle le Prix Nobel vous est décerné. Au nom de l’Académie Royale des Sciences de Suède, j’ai le privilège de vous transmettre mes plus chaleureuses félicitations pour votre travail exceptionnel. Je vous demande maintenant de bien vouloir vous avancer pour recevoir votre prix Nobel des mains de Sa Majesté le Roi.

Professor Higgs you have together with Professors Englert and Brout found the key to understanding the masses of elementary particles for which you have been awarded the Nobel Prize. On behalf of the Royal Swedish Academy of Sciences it is my privilege to convey to you my warmest congratulations for your outstanding work. I now ask you to step forward to receive your Nobel Prize from the hands of His Majesty the King.