Gerardus 't Hooft


Interview, December 1999

Interview with Professor Gerardus ‘t Hooft in December 1999. The interviewers are Professor Per Carlson, KTH Royal Institute of Technology, and Jasmina Cirgic, student.

Professor ‘t Hooft talks about his views on the need for unification in physics, about his hobbies and interest in music (5:02), how he works on mathematical equations (6:50), why he developed his interest in physics (8:23), what can be done to increase the number of physics students (10:39), developments in his field (14:42), his interest in subjects other than physics (21:04), the difference between electrons and black holes (22:23), and how the electronic revolution is changing our world (24:18).

Interview transcript

Professor ‘t Hooft, a key word in physics today, or one of the key words, is unification. There is a lot to talk about unification of forces, according to your mind is unification necessary?

Gerardus ‘t Hooft: Usually there is a danger that one overemphasises the need for unification; it’s rather the other way around. The need in physics is understanding how things work and every now and then we have different regions of physics or different kind of forces or whatever, which give a problem when you try to combine them. We’re meeting problems and we understand that the situation as it exists is then not satisfactory because their forces cannot be combined in a proper way. We need in the overlap region a better theory that takes account of both sets of features of physics, say quantum mechanics and productivity or the weak force and the electromagnetic force or any such sort of different regions of physics where we have different forces or different phenomena which have to be combined. Then we won’t understand how it works and finally in practice the situation is very often this way that once we understood how to combine these different features in physics that you discover much to your surprise, that the utter theory contains more unification, it unifies.

But there’s a danger. People sometimes want to unify just for sake of unifying and then it doesn’t work. I’ve seen various examples of attempts to unify things which don’t need to be unified. There are examples of forces in nature which work perfectly well together without any further unification so then it is not necessary to unify. Then the attempt to unify may be misleading, we see this fairly often, say in the old days, when the elements were being discussed. The big question was how many elements do we have? Three elements, four elements? Water, fire, earth – how many? The correct answer turned to be 92 and more elements. There’s no unification, these were the elements and that was the correct answer. The attempt to unify was given more emphasis than it turned out to be correct at that stage of physics. Later we would discover how all the elements actually consist of the same kinds of matter but that had to be postponed until a different region of physics was being opened up.

The December issue of Scientific American has a theme what science will be known in 2050 and Steven Weinberg there says that to unify the forces we need revolutionary new ideas in theoretical physics. Do you agree with that?

Gerardus ‘t Hooft: Not necessarily, I think in this case he is correct but again, I will not put the emphasis on unification, I would put the emphasis on combined understanding. Right now we have a very deep problem in physics which is that on the one hand we have a theory of general relativity which describes the gravitational force in a remarkably accurate and beautiful way, so everybody believes general relativity is basically correct, a correct description of the gravitational force. On the other hand we also have quantum mechanics, quantum mechanics is an equally beautiful theory. The strange thing is that general relativity and quantum mechanics don’t seem to go together. There’s something very strange in physics. We have different sets of laws of physics, both are right, but they don’t go together. The point being that the domain of physics for quantum mechanics is relevant and the domain of physics where general relatively is valid in the ordinary experiences are very, very far separated. In ordinary experiments we never see the domain of physics where these two come together. But we can always fantasise, we can do Gedanken experiments and we can try to think what happens if both theories have to be applied together, then what? Very likely the resolution of this very deep problem will imply a kind of new unification but I think it’s dangerous to first try to unify and then try to understand. Its better first try to understand what’s going on and then we will see that the new theory will be more unified than before.

Do you have any hobbies? Something you like to do in your free time?

Gerardus ‘t Hooft: Oh yes, that’s quite a different question. I play some piano, I used to paint a lot to make pictures, drawings, for some time I haven’t done that anymore. Then I also collect shells which is a hobby of mine because every now and then I come to strange places for conferences, very often there is a beach so I like to go across that beach and pick up shells. It’s a very nice, you are alone with the sea and the sand and nothing else and I let my mind wander away. In the meantime I try to pick up beautiful shells. So that’s a hobby.

I know that you practice music, often even together with your wife. What does music mean to your physics research?

Gerardus ‘t Hooft: For me it’s just a way to relax. I never went into music in the same deep way as I went into physics. I realised that those composers whose music I like to play, like Beethoven, Mozart, Chopin, Debussy, that they are so far ahead in their expertise than I am that I can never improve on what they wrote down so I just play what they wrote. Because of this I realise that I’ll never be a very good musician because very good musicians they understand, they won’t play what somebody else has composed, they want to play their own pieces. I realised that I am playing music as an amateur but I like to do it just to relax.

In your work you have a lot of rather complicated mathematical equations and I wonder when you think about them can you think about them or do you have to write them down or can you think about them while you walk in the wood or something?

Gerardus ‘t Hooft: Both. What happens is that very often I think very deeply, I write down equations, try to work them out and run into problems because very often the equations are too complicated to solve or some other obstacle is found on my way and I don’t understand how to get beyond that obstacle. Then I sometimes have to relax and I’ll just sleep or something else and while just sleeping I try to simplify the problem as much as possible. I realise there here is this obstacle, what was the cause of this obstacle? Why couldn’t I solve it? There’s some very deep problem here, the equations were too complicated so now I do everything in my mind and then I’m forced to simplify. I simplify and I simplify and simplify and then the obstacle stands out very, very clearly and when you simplify things so much you often find a way around the obstacle. Next morning I go to my work and I work on the equations and I find the answer. That’s the way I very often work.

How did you develop your interest in physics and research?

Gerardus ‘t Hooft: From a very early age on I was interested in the laws of matter, of the abstract things in contrast to human beings who I thought they are far too complicated ever to understand. I didn’t understand, as a kid you, the human relations very well or what happened there just too complicated to me but on the contrary the laws of physics seemed to be honest, there’s no way to cheat on the laws of physics. Understanding those I thought would be much easier and much more interesting. From a very early age on I wanted to understand the laws of physics and I set myself as a goal to make new discoveries. I was thinking of making inventions but then later that became discoveries, I wanted to understand the laws, and that is as far as I remember. In the aeroplane to Stockholm here my mother gave me a picture taken of me when I was two years old and in the picture you see that I am studying a wheel and I’m really studying it, I want to understand what is a wheel, what makes it so special? Later, I don’t remember of course when I was two years old and I was studying a wheel, but I do remember that later I happened to see two wheels touching each other, of children’ bicycles or something like that, and you rotate one wheel and the other wheel starts to rotate as well, the transmission, and I was really intrigued by that. Those were laws of physics and I remember that I wanted to understand laws of physics. I remember that I always was very intrigued by what this world was made of and why. Then besides there were stories in my family and of course the heroes like Einstein and Planck and Schrödinger and so on who made all their beautiful discoveries and I wanted to be like them.

In many countries the number of students interested in science seems to be decreasing. What is the situation in your country and what do you think can be done about it?

Gerardus ‘t Hooft: The situation in my country is the same. The interest in science is decreasing at a rather alarming rate and we try to understand why that is so. I’m afraid I do understand why it is so, our field of physics and physics in general, it doesn’t have the glamour it use to have. Shortly after World War there was nuclear physics, there were the semi-conductors, the super-conductors, all these beautiful, marvellous, revolutionary inventions which were portrayed enormous big in the media and caught everybody’s imagination. The more recent achievements of physics do not compare with those. We still find very many interesting things in physics, but they don’t catch the same imagination and interest by the people because it gets to abstract, people don’t understand any more what science is. When the glamour is taken away they now see all the negative sides of science, they see the negative sides of nuclear physics, they see the negative side of too much television. Science is put in a much more negative light than it used to be and I think as a consequence people are turning away from science. On top of that what irritates me rather a bit is that on very many popular movies and scenes on television, television is a very important medium, so very often on television you see a movie and the big hero is never a scientist, the big hero is a lawyer. The kids are inspired by that, they want to be a lawyer just like the hero they see on television. I can’t blame them, I think it’s understandable what’s happening but of course we don’t like it.

A somewhat related question is a question of women in science. If we look back to the Nobel Prizes during the 20th century, they’re almost all or a majority are men. Do you think the same will be true for the 21st century or will there be a change?

Gerardus ‘t Hooft: I’ve no idea. I don’t see why women should be any worse scientists than men so that’s for certain. But indeed, as you say, in practice it is men who make the big discoveries, at least percentage wise much more of them than women. I’m sure it doesn’t have to be like this. What the cause of this is I do not understand, I don’t know. I can guess but my guess won’t be any better than your guess what the cause of that is.

Are there any special moves in that direction in Holland, to interest girls in science in the early ages?

Gerardus ‘t Hooft: Of course you always try to get girls interested in science. Unfortunately in my field it seems as if theoretical physics is an absolute minimum. There’s practically no branch of science with fewer girls or women in that branch of science than theoretical physics, even in mathematics or experimental physics or other branches of science you see more women but not in theoretical physics. I think it’s very unfortunate. I wish it were different.

What do you think is different between being a student today and when you were a student?

Gerardus ‘t Hooft: Our field is evolving very rapidly. In my field, but now I’m only talking about my field, these 30 years since we made our discoveries enormously much has happened. It’s very unfortunate but there are developments in our field that nobody could foresee and nobody can change but it seems to be that the most ardent questions in our field are those which we mentioned earlier in this interview. We mentioned about Weinberg, unification of gravitation and practical physics but it is very unlikely that one will be able to do direct experiments in such a field. That is a big change, when we did our work experimental physics and theoretical physics were going hand in hand and they are together solving the problems of our world. Now the experimentalists have a very hard time in getting deeper into the structure of matter because they have to be extremely clever, they make very, very large machines and they get effect of 10 improvement in resolving the structure of matter and its always very important, then perhaps another factor of 10 very important. But in our field, in theoretical physics, you’re not talking about factors of 10 but about 10 factors of 10 so factors of 10 billion or even 100’s of millions of billions. Such factors where the unification of gravity with matter becomes important. Unfortunately we cannot make a machine that is 10 billion times as powerful as the machines we have at present, those would have to be 10 billion times as big and that we cannot make. Experiments cannot be done at that stage. That means that these are very esoteric regions of physics, very abstract and very vague and mysterious and it worries me a lot that this may perhaps not be physics at all. The striking thing is that nevertheless in spite of the absence of direct experiments progress is being made very, very slowly and I don’t know how things will continue in the future but that is very a big difference with what our field was thirty years ago.

There is a lot of talk about the elusive Higgs particle and how important it would be. What would be the consequences according to you if it is not found?

Gerardus ‘t Hooft: The present theory does predict the Higgs. If it is not found then the theory would not really work properly. In fact the situation would become very confusing at those energy scales where we would have expected the Higgs. If the Higgs is not found there then something else must happen. In practice some kind of particle must exist in place of all of the Higgs. One thing is that the Higgs doesn’t have to be an elementary particle, it could be a composite object. That is not so strange, that has been thought of many times before and it could be a possibility. But if that is so then we have to understand all those new forces at work which create composite particles at that energy range and it would definitely mean that there is very, very much new physics taking place. The way theory is now, a theory with no Higgs is not very different to a theory where the Higgs is very, very heavy. Having no Higgs is in some formal sense the limit where the Higgs mass goes to infinity. That limit is ill-defined, the theory is ill-defined you have to have something else going on then.

If they find no Higgs at all that will make our world much more interesting than if they find a Higgs exactly in the region where most people expect it, because then we don’t need new physics just around the corner. If there’s no Higgs we need no physics and that means that the future machines which will increase their power by a factor of 10 or a factor of 100, those new machines will produce many, many new objects which we have no idea about at present. Quite generally speaking it would make life very interesting if they don’t find the Higgs where it is expected to be. But I think they will find the Higgs and I think it will be found where it is expected to be and then the problem is of course what then, because then the standard model again shows that it survives another factor of 10 and no /- – -/ need for further particles is there although the standard model as it is it cannot be the ultimate truth. Now it’s not obvious that new machines will find anything new even if they get a factor 100 or so beyond the present energy. We simply will be in a more difficult situation if they do find a Higgs. In any case, whatever they will find, no Higgs or Higgs it will always be interesting because we have no good clue as to why the Higgs has the mass it has. No matter what, the Higgs could be 100 gv it could be a 1,000 gv or anything in between or when its 2,000 that’s practically synonymous to having no Higgs and that would make the world very, very interesting. In all these cases you have to ask the next question: Why this particular Higgs mass?

I wonder is there some subject except physics that you’re interested in?

Gerardus ‘t Hooft: I like to read the science pages of the newspapers, in particular astronomy, so I very much like to see the features defined in other planets. I like the recent discoveries in the recent field of biology, I’ve read this book by Dawkins, The selfish gene and this was a revelation to me that finally biology is becoming scientific as far as I am concerned. I didn’t understand biology before because my teachers used to say that birds have wings otherwise they can’t fly but that wasn’t a satisfactory explanation to me, other creatures have no wings and they don’t need to fly. Why are there birds with wings and why are there birds without wings and so on. There may need to be other answers and those new developments answer that question in a much more satisfactory way than I’ve seen before. I like those branches of science.

One of the questions coming in to the Nobel site from students is the following, it’s about the electron and the question is the following: Now the electron is known to be or assumed to be point like particle, still it has a mask. It is therefore considered to be a tiny black hole?

Gerardus ‘t Hooft: You might if you want call the electron a tiny black hole but it doesn’t make sense. The reason is that the electron is too light. If you were to compute the size of that black hole you would get a size much, much smaller than was believed to be the smallest existing size in nature. When you try to describe it as black hole you are pushing things too far. However, there’s another thing we might consider which is the point like particles such as electrons, neurons and heavier particles, they form whole families and it is not obvious whether they are the most heaviest point particles, it’s not clear where it will stop, so there could be heavier and heavier and heavier particles. Eventually those particles might blend with the black holes but only if they are billions and billions times as heavy as the electron. Then it becomes sensible to describe such particles as black holes but not particles as light as the electron. It could be that there’s a gradual change from black holes to particles and that the exact boundary, this is a particle, this is a black hole, the exact boundary may be not impossible to indicate or be irrelevant. But to call the electron a black hole wouldn’t make much sense.

The last few decades has seen a very rapid development of electronic communication and electronic publishing. What does it mean for collaboration between scientists, do you think?

Gerardus ‘t Hooft: It changes our world. Nowadays scientists are using internet all the time and we send all our papers to the net and it seems as if the net is replacing already the scientific journals much to the regret of the publishers. In practice we find that those journals are hardly needed any more because we have all those papers which are on the internet so whenever someone wants a paper one just clicks into the internet site and finds the paper and we don’t have to look up the journal anymore, its quicker. In practice the electronic revolution – and I think it is a revolution – is changing our field dramatically. I don’t know what will be coming next, I’m looking forward to the time in the distant future when it will be unnecessary to use paper anymore, that we only work from screens. Right now the situation is still such that although we use the screen to write our papers and to devise our texts in practice whenever we want to study the paper we make a printout and we make all this waste of paper. Since the electronic revolution more paper is being used than before because we all make these printouts. I’m wondering when that will end, that we will no longer feel the need to make a printout because the screen is so versatile and so flexible that it’s easier to work with the screen and it’s no longer necessary or sensible to make a printout. But that will be the distant future.

The electronic age, would that change in any way the competition between individuals or groups working?

Gerardus ‘t Hooft: I think it makes the competition a bit more honest at least for those people who have access to the internet. Everybody with access to the internet and nowadays it is nearly everybody even developing countries have access to internet at least many of them and they can now participate in the process. They don’t have to subscribe to expensive journals because they can link onto any of the papers that any other groups could also reach. You can find everything on the net. As soon as you have access to the net you can participate fully with the whole process of science, at least in my field because the theoretical physics as you know basically requires just pure thought and you are processing the experimental data which can also be found on the net and in theory that’s all you really need, at least in my field. In former days it was more difficult to get hold of information particularly if you were living in either a developing country or in the old days in the Cold War when you were behind the iron curtain it was very hard to get information in time. People were often half a year or so behind developments because they couldn’t get the information. That has not changed. On the other hand of course if there are countries which are so poor that they don’t have the access to the computers, access to the net and then you have a problem, those really can’t participate.

Thank you very much for this interview, Professor Hooft. Thank you very much.

Gerardus ‘t Hooft: Thank you.

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