Interview with François Englert on 6 December 2013, during the Nobel Week in Stockholm, Sweden.

Could you describe your Nobel Prize awarded work for young students?

François Englert: First I will tell them or remind them if they know a little bit that all the matter that we have around us is composed of atoms. The atoms are kind of mini solar system, not quite, but nevertheless it’s an image, and in the middle there is an nucleus which is round. And for a long time this was supposed, the whole the atom, to be not … that it was not possible to cut it and to separate it, but now we know that it is. Inside the atom there are particles which are called quarks and other particles of all kind which of the constituent fundamental of matter which are what called elementary particles and there are also other elementary particles which are constituent of things which are transmitted from one object to another like photons which are constituents of light and there are other ones. Some of these particles have no mass and some have mass. Photons have no mass and the characteristic of mass is normally when you push it, it’s very difficult, if it’s a high mass it’s very difficult to push it.

But the more detailed meaning of what it means is that those particles which have no mass travel, whatever you do, with the same velocity which is the velocity of light. Particles which have mass never reach the velocity of light, so that’s the big distinction between the two. The problem was that one did not succeed to make a theory which could predict what one could do with this elementary particle. In particular we know what we can do of them, everything that is around us, whether it’s that glass, whether it’s the door, whether it’s this television apparatus whatever. We can do all of that, but the recipe for doing that was not really well known and one particular difficulty is that one could imagine constructing a recipe which would work if all particles which have no mass. If all particles which have no mass, then one could indeed form a formula which would predict everything but that would result in predicting nothing because after all that is not the world that we live in.

So we were obliged to invent how particles which have no mass can acquire mass, some of them at least, and some not. For this we imagined at that moment some particles, bosons, scale bosons, whatever the name is on it and that condense to give kind of a sea, but a sea that exists all over the universe so that every particle has to go through it, including ourselves. So the elementary particle that goes through them can acquire a mass if they are sensitive to this, that is more complicated to understand, but the theory predicts which are the particle which will get a mass and those which will not get a mass. That essentially permitted to construct the recipe for doing the thing and the important thing of course is that from this condensation it is possible to extract one particle and test if the theory is correct and that is what has been done at CERN. I don’t know if a 13-14 years old will get something, but I hope they will at least get a little bit interested.

Why did you go into science?

François Englert: When I was in secondary school I was actually interested very much in literature but I was also very much interested in mathematics. My teacher in mathematics, I liked him very much, I think it’s about the only one I liked when I was in the secondary school. I had a very good relation with him. I was not a bad student, so he pushed me to enter the polytechnic school for engineering. This was also partly because engineering in Belgium requires an entrance examination which is very hard, actually in three places if you wish the diploma of secondary school. You don’t have to do secondary school if you succeed that exam. He prepared me for that exam, so I was an engineer. Being an engineer, I realized that I don’t want to be an engineer, but I was an engineer so that gave me … I realized by being an engineer that what interested me is not so much the application of things but the way they really function. That is why I got interested in physics and research and fundamental physics. After having been engineer I got sufficient money because I had a job at the university, and I studied physics afterwards. Then I had my PhD and then I went to the United States and met Robert Brout with whom I collaborated a lot and that’s in a short hand the story.

Who is your role model, and why?

François Englert: There is one person which I consider as an extraordinary physicist at that time I knew him. He is a man of extraordinary humanity, that is Nambu, in fact who got the Nobel Prize by the way. And he was the one who introduced the essential notion which was essential for doing the model which was taken from the theory of phase transition in solid … statistical theory of solid objects and to field theory, which I liked. I was interested by many people who did it, but I think I generally wanted … and Robert Brout was famous like me, we wanted to work things by ourselves. But Nambu played an important role, that is for sure.

At what point did you realize your work was a breakthrough?

François Englert: I think we realized it nearly immediately, I can tell you something about that. To be clear our work was kind of a general theory, we were not sure to what it would apply. Actually, we thought first it would apply to the strong forces which was a mistake, but we then realized it applied to electroweak forces. But we didn’t make the theory, that was won by Weinberg, Salam and Glashow who had the Nobel Prize for that and there have been a lot of Nobel Prize connected to this theory. First the Nobel Prize for the electroweak theory, the Nobel Prize for the fact – which was very important and which we were completely aware of from the beginning – which is the fact that it’s valid quantum mechanically which was proven in a beautiful way by Dr. Veltman, they got the Nobel Prize. There was a discovery by particles at CERN the W and the Z boson which transmute … which have mass and transmit the weak interaction and that was also a Nobel Prize.

All of these were essentially the base to particles to what we have constructed as a theory but of course there is a lot of things to be added to get all of that and it took time. The point is that after let’s say -83, 1983 when world discovered the W and the Z we were totally convinced that the theory was two, but there was still an alternative. Either it was mediated by a condensate of objects, the sea, which was not the boson, or it was the bosons, which were condensate. We in our original paper put both hypotheses and didn’t know which was the right one and at that moment in- 83 it was still untrue, which was the right one and it is the discovery at CERN that would select the right one which is one of the two hypotheses we put in -64.

So I have a bit deviated from your question which is when did we realize, of course we didn’t realize all of that, that’s obvious, but we realized that I think it was a break-through, because we saw that it was the first time there is a way to understand how interaction, fundamental interaction which acts between objects which are very close to them and are not felt at large distances – that is called short-range interaction – that that could work, and so I remember with Robert Brout, who was my friend, and we worked together after that also for years, that we went to a café that I still see very well and we ordered a bottle of champagne and we said … and that was I think a few months after having had the article, so that we had the impression. We were a little bit sad that people didn’t seem to realize that or to pay attention, let’s say. There were good reason not to pay attention at that time, because there were lots of things. But I think we had the right. We were convinced by the way we did it, we didn’t have a proof at that time that it was consistent quantum mechanically, but the way we constructed it – which is very peculiar at that time – it’s based on what’s called field theory and we had the impression that that at the end would work and so we celebrated, we might have celebrated wrongly, but at least we got the champagne and that was fine.

Could you explain the standard model?

François Englert: The standard model is precisely what classifies all these particles from which we can construct the whole world. Actually, the standard model contains essentially all these quarks, these electrons that constitute the atoms, all the other elementary particles that one can construct out of them, or then out of collisions, and it contains … describes the force which are /---/ them and that is essentially the recipe because the forces are also transmitted by some elementary particles some which have mass, some which don’t have mass, photons have no mass, those which give the so-called weak interaction give mass. Essentially there are three kinds of interaction which are included in the standard model: the electromagnetic interaction, the weak interaction, which are responsible in particular for the disintegration, radioactive decay, and these two were united in a theory that make a very deep use of our theory which was then in a quite general frame. And the standard model contains in addition strong interaction which also are interaction between objects which are inside the nucleus, but which are responsible for essentially the cohesion of these nuclei. These are the strong interactions which are not explained by our theory but by something different, which actually is essentially related to our theory by something which is called, let’s say it’s the opposite. The opposite of something is not necessarily very distinct, that it is.

These are the three types of interaction which form these particles that we know today that are hold together and getting a mass with this boson that was discovered or rather by the sea of them which gives this sea which permeates the universe and there is another interaction which we feel every day, which is gravitation  which is what … we let an object fall and it falls and why the planets turn around the earth,and why everything like that works and that is also a theory, but for the moment it is not included in the standard model. It is something apart, we know it very well, it is the first thing that was known, it was redeveloped by Einstein and generalized by Einstein, it’s called – a bad name, but it is called general relativity. That was in the beginning of the 20th century and, so, that is very well known, but it has its difficulties and not, I don’t know if you want to enter into that, that’s more complicated.

What were you doing when you got the message of being awarded the Nobel Prize?

François Englert: First it took some time to hear it because there was some delay. When I was there, three of my daughters were with me and my wife, because after all it was quite possible, it was not totally unexpected that I would get it, let’s say, the Nobel Prize. So we were waiting and then we had decided that for some reason either they did not give it for the theory this year or whatever, my daughter were not quite nice with what they said about the Nobel Committee at that time because they thought that we don’t get it, but then the call came and so I was of course extremely happy and so were my daughters and my wife.

Watch the interview

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