What is Quantum Mechanics, really? | Interview with Dr. Gerard ’t Hooft

0:00:12.9Getting into Physics

Jed Macosko: Hi, this is Dr. Jed Macosko at Wake Forest University and AcademicInfluence. Today we have visiting us from Europe, Gerard ’t Hooft, which is a little tricky for us Americans to say, but he’s from the University of Utrecht, and he is a theoretical physicist. And so, one of the things that I think our visitors to our website would like to know is

how does one get started as a theoretical physicist. What led you into this field?

Gerard ’t Hooft: Well, yes, for me, this was an easy thing to do. I had some scientists in my family, and when I was very young my grand-uncle, I think it was 1956, received the Nobel Prize for Physics. And of course, in the family, this was a very important event, and so I learned about physics and about being able to do the kind of work in physics that earn you a Nobel Prize.

But most importantly, physics was an upcoming... A new... No notion in the world. You have to remember, I was born shortly after the Second World War. And the World War had been ended by atomic bombs on Japan and nuclear energy was on everybody’s mind about changing the future, except that physicists didn’t really understand what was happening inside the nucleus of an atom. They understood more or less how the electrons allowed the atom behave, but not how the nuclei behave. So there are very many mysteries.

Also, as a little kid I saw the first television emerging, it was black and white, and it was very difficult to handle, but those were the first televisions. People were talking about computers. So physics was a very exciting field and very imaginative for me to realize that I wanted to become a physicist.

Even when I was an even smaller kid, I was plagued by difficulties in understanding how humans behave, when are you being punished for something and when not, and what is right and what is wrong. I found these things very difficult to understand. But if you hold a ball in your hand and you drop it, it always falls down, and that is very easy to understand. So I thought that natural phenomena were much easier to understand than cultural phenomena. And so I wanted to become a physicist. I wanted to research the world of science and I wanted to be good at it. So I also learned that mathematics is very important, to combine that with your understanding of the physical world, so I was also very much interested in mathematics.

And I’m also fortunate to have another theoretical physicist in my family, my uncle, Professor van Kampen, who became professor of theoretical physics at Utrecht. I grew up in the Hague, not so very far from Utrecht. But another university town, Leiden, would have been closer to me, but I went to Utrecht just because I wanted to follow the lecture courses of my uncle. Because very often when I asked him questions about physics, he would say that’s too complicated to explain to you. Come to the university, make sure you get out of that school as quickly as you can and go to university, follow lectures there, and I’ll tell you exactly what the answers to your questions are.

0:04:10.3Phase-contrast microscopy

Jed: Do you feel like you’ve learned enough to, let’s say, understand what your great-uncle got his Nobel Prize for? What was that?

Gerard ’t: At the time it was a difficult topic. He had gained the prize for inventing a new way to do microscopy to use as an essential source of information, not so much the intensity of light, but the wavelength, the phases of the wavelength of light. And that was a new discovery that made microscopes much, much more useful, particular in living organisms. So he could, for the first time, make a video of a cell which is dividing in two. And you could see the chromosomes of the cell, of a living cell, you didn’t have to put dyes in the cell to make the cell visible, but you could have living cells in the amnio microscope. So that was an important discovery at the time.

Jed: And we use that type of microscopy to this day? It...

Gerard ’t: Yes, although today there are many other competing methods to make...

Jed: But this is phase-contrast microscopy?

Gerard ’t: This is a phase-contrast microscopy.

Jed: That is a real first line of attack for cells when you’re looking at them in the incubator to see if they have properly grown, everyone uses phase-contrast microscopy.

Gerard ’t: But you have to understand this are the 1950s, and so there were not yet many competing ways to do microscopy. Nowadays you can also look at the polarization of light and translate that into colors and well, you probably know that there’s also electron microscopes, which have a much, much larger capacity of magnification than optical microscopes. But in those days this was an important new development.

0:06:09.7Choosing theoretical physics

Jed: Well, it’s definitely important. Certainly worth a Nobel Prize. So it sounds like your great-uncle did things that were more practical for physics, whereas your uncle did more theoretical physics. Obviously you had a choice between the two different kinds of physics.

How did you choose theoretical physics over more developing techniques type of physics?

Gerard ’t: Well, indeed, my grand-uncle was considered by some to be one of the last scientists who were both very good in doing experiments and good in theorizing about the experiments. He knew how to do the theoretical calculation and how to set up the experiments, so he actually made a phase-contrast microscope with his own hands. He first went to the Zeiss company to ask them to make a lens of a particular kind and the letter he got in response from the Zeiss company was that if this is anything important, they would have made it themselves, so there’s no use to do anything for you. So he decided to make his own lens and to polish his own lens and to... According to his own specifications, and it worked, so he could make his telescope. And he has other things, he also had a galvanometer which was more sensitive than existing galvanometers of those days.

Jed: What a true scientist! So was it because there was not as much opportunity for being both a theoretical scientist and an experimental scientist in our day, now that we’ve moved to more specialization, is that why you decided to have to choose between the two?

Gerard ’t: Yeah. In the early days, the divide between experimental physics and theoretical physics was not so great as it is now. So nowadays, you really have to choose. Even when I was a student at Utrecht, they demanded, it was a demand for theoretical physics students to also spend half a year in an experimental facility to assist in experiments and it was part of your curriculum. And for me, it was very important, I was... They put me as an experiment in solid-state physics and I had to put crystals in liquid air and put them in a microwave installation that investigated those crystals with microwaves and figure out what do you see there, well, how do you determine the electro-dynamical properties of crystals of different kinds of metals. So that was very useful to me at that time to get some feeling about what experimental physics is.

You carry around dewars with liquid air everywhere. That’s experimental physics for me. My teacher Veltman was even more of that kind, that he was very much interested in how to understand, how experimentals detect particles. What can you do? What can you see if you want to understand the particles under which an atomic nucleus is made? How do you make them visible and how can you study those? And he thought these questions are very important also for a theoretician to know.

But eventually you have to choose where are your strengths, and I didn’t like the organizational part of an experiment. Experiments, you always have to do with very many scientists all having their own jobs, so I have to be very good in social skills to have a whole team working on a big experiment, and my social skills are not so good, so I’ll never be able to organize things properly. I want to do the calculations myself and I still work that way. I’m sort of an exception, most of my colleagues, even in theoretical physics, they work together with small teams, but I’m not so very good at that, so I work mostly alone.

0:10:16.1Contributions

Jed: You’ve obviously been successful with your way of doing things. We recently interviewed Misha Shifman at the University of Minnesota, and he was telling us about some of the revolutions in the understanding of what is inside of an atom that happened during the 1970s.

So that is right around the time you were learning theoretical physics, and what kinds of contributions have you made in that area or in other areas?

Gerard ’t: Well, that’s a difficult question to answer completely. I’m biased because we had the feeling before 1970 that the field was sort of in a slight impasse, we didn’t really understand how to build up theories which were as solid as existing theories, the other existing theories. So we knew one of the three or maybe four forces that act on elementary particles. Only one of these forces was understood really in some detail, and this was the electromagnetism. So we knew how particles can get the electric charges, how the electric charges generate magnetic fields and charges, and what the equations for this theory are, and how it all hangs together. And these theories could be checked to amazing accuracy. So one could measure the magnetic moment of the electron and calculate it, and both operations could be done very, very precisely so it would very precisely match the theoretical results against the experimental observations and see that they agree.

So the electromagnetic force was understood but not the other forces, or not at all, really. So my advisor at that time, Tini Veltman, who just very recently, a month ago, deceased, but now he was very much aware of the fact that this situation could be improved, and he investigated of those interactions, in particular, the weak interaction.

In those days, you didn’t talk about electro weak, that’s a later invention, because it was only later discovered how intimately the weak forces are linked to, related to the electric and magnetic forces. It’s basically one grand scheme. So you could call it a unified theory, but that’s a little bit, too much all... unified. It’s not completely unified, but the similarities between the forces are very significant and they mix, so when you have one force, you always have the other force as well.

And in the early days, it was not understood how to make this theory any way close to be as accurate as electromagnetism. You could only make very rough first order calculations, but when you wanted to make corrections, because you knew you were neglecting certain effects that you should take into account, you could do that, but the results would be meaningless expressions usually containing infinity as an answer, but nothing is infinite in the physical world.

So that was clearly wrong and how to do corrections turned out to be very difficult. And my advisor had gotten a long way in doing that, but not yet completely. So together already we could... We could find the answers of the question how to do accurate calculations here and how to get ahead of all those infinite meaningless answers, and also how to check theories against experiments, so right after that we could publish our results, realized mechanic models, a model is just a set of equations that altogether should be self-consistent and should give description to some accuracy of the behaviour of particles or anything else that you want to describe.

So people suddenly had learned how to make models because models had to obey certain... Essentially certain constraints. And that put our whole field in a new kind of acceleration. And the 1970s turned out to be a splendid time for our field because lots of new discoveries were made in short succession. We were having a breakthrough of various kinds, and I was involved in several of these, but the first act of finding the exact answers to the questions for the weak force was really the first breakthrough, and perhaps for that reason, also the most important ones, because... Of course, other scientists will disagree what they find as the most important development, because at the same time, people made lots of progress understanding the strong force. There are strong force and weak force in electromagnetism, and people started to think about gravitation. But gravitation is another quite a different topic, very difficult to do any experiments with, certainly when it is considered for elementary particles inside an atom.

But we started to see for the first time that the different forces that act on elementary particles can all come together into one grand scheme. And many people thought that we are very close to understanding the entire scheme of all the forces on particles. That didn’t materialize quite as easily as people hoped for. But this last big avalanche in the 1970s was just a great moment to enter into a new field.

0:16:17.3Thoughts on supersymmetry

Jed: Yes, it’s been amazing. And in talking with Misha Shifman, it seems that he is still holding out for supersymmetry. And that even though the LHC did not show that, he thinks that a larger collider might be able to show that.

What are your feelings about what Misha has been championing for many years about supersymmetry, other people, which it didn’t seem like it really panned out as well as some people had hoped. What are your thoughts about that?

Gerard ’t: Well, I never put my cards really in supersymmetry. It is a lovely mathematical scheme, and I think that is what all people agree about and certainly Misha Shifman, who I know very well, has done marvelous jobs in exploiting as much as you can the mathematics of supersymmetry, so how does supersymmetry help you to do complicated calculations? If you assume some system of forces can be supersymmetric, many calculations simplify so much that you can say, many, many other things about these forces which otherwise would be impossible to understand. So mathematically, theoretically supersymmetry is a great concept.

I’ve not worked so much on it because I thought supersymmetry was not the answer to my questions about theoretical physics itself, about where do the forces come from in nature. So many people think indeed supersymmetry is sort of the beginning of an answer, but I’ve never seen the need for supersymmetry in as such an elementary way as many people in my field do think, like Misha Shifman is one of them, but there’s quite a few others, who also suspect that supersymmetry must be a very important ingredient in a fundamental theory.

Jed: And it must...

Gerard ’t: I don’t quite agree with that. So it’s not really a must.

Jed: Yeah.

Gerard ’t: It’s probably just a mathematical curiosity, which is very good to exploit and to learn, to understand how things hang together, but eventually, nature itself doesn’t care so much of supersymmetry; in fact nature itself doesn’t care much even about quantum mechanics, or about all your sacred notions that they have today, just because I still believe that the real fundamental equations for an all-embracing theory are something that they haven’t even come close to. Supersymmetry may or may not be part of that. I don’t care in which direction it goes, I want to understand more deeper coherence between all the physical phenomena and particular forces among particles.

Jed: Fascinating. So you just are wanting to know what’s happening, and a lot of people like Misha see supersymmetry as a beautiful theorem, mathematically beautiful, so beautiful that he said that it must be true, [chuckle] but you’re not so convinced.

Gerard ’t: That sometimes helps, but it only helps in the other direction. If a theory is correct, it always turns out to be beautiful, but if a theory is beautiful, it doesn’t always turn out to be correct, and we have many examples of...

[overlapping conversation]

0:19:37.6Quantum mechanics

Jed: That’s a good piece of advice. Well, it’s interesting that you said that quantum mechanics might also be something that nature doesn’t care about.

Have you seen problems with the sort of formulation that we humans have given to quantum mechanics and that there’s problems?

Gerard ’t: No, quite the contrary. Many people see problems with quantum mechanics as a pure theory because it seems as if quantum mechanics is not describing a reality, it looks as if quantum mechanics is doing away with notions that we thought were central in our existence, like there’s a reality around us, the world really exists around us, there’s one universe and things happen or do not happen, but if we say things happen perhaps or with a certain probability, then that’s because we are unable to do the calculations exactly, so...

Jed: So do you think...

Gerard ’t: The weather, for instance, so we can only say probably it’s going to rain or there’s going to be some snow or it’s going to be sunny, and we can calculate probabilities. So no theoretical physicist should be ashamed of the fact that physics only calculates probabilities.

But in quantum mechanics, we are doing something else. We are suggesting that the very nature of the phenomena in physics are uncertain and that there is one blurry universe of blurry certainties or uncertainties, and there are other blurry universes surrounding that. I think that’s basically wrong, I think all these... The situation that we are presently in is just a consequence of our ignorance. Yes, we are only primates in physics, we are just having enough intelligence to investigate laws of nature. Only a few thousand years ago, nothing of this was even approximately true. And we have still millions of years to go as a civilization to totally transform our science and everything else, and the fact that only after a few centuries of intensive investigation science that those first few centuries brought us a theory with uncertainties in it, is quite understandable.

There’s nothing nothing wrong with that. It just means that we haven’t even come close to the tools yet. But for me it’s not enough to conclude from that that you shouldn’t work with certainties, I think one should, and I can see the mathematical links between the quantum mechanical equations and perfectly classical equations, perhaps so much more sharper than some other people, and so I see the mathematics of quantum mechanics has all the ingredients to change it into a completely deterministic theory. People who say otherwise haven’t really come to the bottom of it yet.

Jed: So, would you say that the problem with quantum mechanics was sort of that the physics community went with the Copenhagen interpretation of quantum mechanics, and were there other early interpretations that may have not given rise to this blurry universe with other blurry universes around it? Would that have been a possibility if things had been different in history?

Gerard ’t: Well, I maybe repeat the question for a moment. It’s quite the opposite. And the Copenhagen, what’s now called the Copenhagen interpretation, is actually an agreement, like a treaty, let’s not fight so much about the interpretation of quantum mechanics, let’s just look at what the equations say. And the equations say that we have a completely fantastically coherent scheme to understand the mechanical features of particles and fields. Everything is very small, and antiparticles, molecules, photons of lights, just the small and light things of the equations that we call quantum equations.

And the outcome of the Copenhagen discussion was that these equations work so well, we just add a few axioms about how to interpret those crazy wave functions that we talk about, and all is fine, and don’t worry too much about the interpretation.

And actually, that was a very good thing to happen in those days because people couldn’t understand the interpretation of quantum mechanics at all. So when they start to talk about it, you get all these fights and disagreements and uncertainties, mysteries that you’re all immersed in. Whereas if you just stay away from those questions, quantum mechanics is perfect. And there’s nothing, absolutely nothing wrong with it. So even up to this day, people are trying to modify the theory just to make it a little bit more logically coherent. To me, that’s completely the wrong way to go. You shouldn’t modify a theory at all.

You should look at what it says and interpret that literally in terms of something happening at another other scale of science, that where the smallest particles are entities which no longer behave as particles but rather like a fantastic number of gears and levers in a very complicated looking machinery, that machinery is our universe. And only when in those gears and levers in that machinery, some wave-like pattern emerges, we call that a particle. The reason why these particles behave so erratically and so in-deterministically is because you haven’t really understood what the particle is, it’s not that the nature itself should carry uncertainties in its very existence, in its very definition, not at all.

So I have all these ideas about how to do quantum mechanics just in that way, but I find it difficult to explain even to my colleagues exactly how to do this right and I must convince myself. I’m also doing things not yet quite right, there are still mysteries that I want to understand better, but the fact that there are still mysteries that you want to understand better, doesn’t mean that you’re on the wrong track, it just means that there’s some very beautiful coherent scheme, and it’s our job as theoretical physicists to phrase our questions sufficiently precisely to dictate exactly how one should think of things, how to formulate the equations, and that formula is a much more complicated thing than what we are used to. We are used to thinking about particles like planets in the universe, planets that go in their elliptical orbits around the Sun.

We know how to calculate those orbits very precisely and so easy, whereas elementary particles in an atom or electrons or photons behave according to laws which are much more complicated than the laws of planets around stars and suns. But it doesn’t mean that it’s fundamentally different. I think the bottom line is that the equations for elementary particles are just like the equations for planets going around suns, but there’s so much more going on and if you want to formulate a precise theory, you have to be under control of everything. And everything, that’s a bit much to study just as a single person.

So we’re not there yet, and it may take a very long time for us to really understand what’s going on, but I’m completely confident that sooner or later we’ll find the right language, and that’s the basic problem today, to find the right language.

0:28:06.9Your perception

Jed: And I think that finding the right language helps when different scientists have different ways of thinking about it. So for example, you said a lot of people think of quantum mechanics as being this fuzzy universe with other fuzzy universes around it, blurry, and it sounds like you don’t think of the universe like that when you think of... You were mentioning dials and levers that are there, and only when they form a particular wave pattern do we call them particles, is that kind of the way you think of the universe as opposed to thinking of it as this blurry, both states, the cat is dead and it’s alive at the same time. Is that a little bit how you think of it compared to some of your colleagues?

Gerard ’t: Yes, I have... I have written this down. It’s a little book, which I made freely available on the net, and it’s called The Cellular Automaton Interpretation of Quantum Mechanics. The cellular automaton is just a device that can be used as a model for everything in the world that you like to understand.

For instance, the pattern of the weather and the clouds on planet Earth. So think of, you put a big grid across the globe and at every point on the grid, you register the temperature, the wind velocity, the moisture and air pressure, all these data I put on the grid, and then you make sure that you have the equations that link grid points to neighboring grid points and tell you that if the wind velocity is such and the moisture of the air is so, then the moisture of the air in the neighboring grid will be affected by this. And same thing for pressure and all the other properties of weather systems and altogether, you can now just press the button and ask, how does the weather develop.

This is called a cellular automaton, and I think that ultimately, when you look at the world itself that you live in, it is like a cellular automaton, or at least it looks as if it can be modeled by a cellular automaton, except that we don’t really have that grid. We don’t really know how to put a grid on the universe. And one thing we’ve learned from Einstein, we have learned many things from Einstein, and one of them is that a completely angular grid won’t work because there’s the gravitation force, and then there’s tricks on that and it tells you that different observers will use different grids. And to write all these grids, whatever you choose, to write down laws that can be put in a cellular automaton, which you can feed a computer and it can calculate everything is going to be very difficult. But these I find side issues, these are difficulties, and they’ll be part of our elementary language on the long run, so you have to understand how to do this, it’s very difficult.

But it compares a little bit with what computer scientists do. You know today, if you make a picture with your computer, the picture is stored as an array of pixels. Now, horizontally and vertically you have black and white or colored pixels, and if you look at it at a sufficient distance, it looks like a picture and you don’t see the individual pixels anymore. But now what to do is something very clever, if you want to rotate your picture it’s very easy. So you just say rotate for 17.5 degrees, and you get the picture 17.5 degrees rotated, you can blow it up, you can shrink it, and in spite of the fact that we had a rectangular grid, nothing is rectangular anymore in operations that you can apply to these pictures, you always get a good picture.

So I’m quite impressed by what computer scientists can do in this area, and it’s now become so normal that you don’t even think of it, so in other words, if something at the very tiny scale, can we describe it in terms of grid of pixels, then at larger scales, it looks like being a continuous world, and that step has to be understood much, much better than we understand it to apply it in computers, but it’s... Has to be applied to nature itself. And I’m convinced that something like that is possible, but it will be very difficult. So we’ll need much more mathematics to understand exactly how this goes.

Jed: Well, thank you so much. Maybe this interview will inspire the next generation of theoretical physicists.

Gerard ’t: I hope so.

Jed: Who might happen to come to our website and watch it and be encouraged that there are so much more left to be done, so many more discoveries and theories to be worked out. So thank you so much for taking the time today.

Gerard ’t: Yeah, I just want to add to what I said, that’s a sort of standard model, the elementary particles, and I think that came out of many investigations in particle physics, and it tells you what the most basic ingredients are that we understand today. It doesn’t mean that this is a grid, and it doesn’t mean that you know now how to derive a cellular automaton, but I think it’s a very good beginning, and the data that we get from the particle investigations are extremely important to make a beginning of trying to understand nature’s cellular automaton.

0:33:51.6Sign off

Jed: That’s great. Well, these are things that I’m sure will be very encouraging to the younger people out there. And thank you for taking the time to spend with us today. It has been so informative and helpful. Thank you.

Gerard ’t: Thank you.