CERN Accelerating science

Collecting the pieces of the Infinity Puzzle - An Interview with Frank Close

by Panos Charitos

So what is the Infinity Puzzle about?

When quantum electrodynamics was used beyond the simplest approximations it gave nonsense: infinity came as the answer for quantities that have sensible measured values.  This problem was solved in 1947, when a way was found to get rid of infinity and reveal the true values. One of the key factors that contributed to the solution of this puzzle was that the photon, the carrier of the electromagnetic forces, has no mass. Trying to make a theory of the weak force, free of infinity, was however a problem because the carrier of the weak force, the W boson, is a massive particle.  Veltman and 't Hooft  managed to solve the infinity puzzle in 1971 and set the way for the next 40 years of successful physics that led to the LHC and last year’s great discovery of the Higgs boson. By the way, this should not be called the "Higgs-like boson" but rather we should use the lawyer’s term that it is “beyond any reasonable doubt” the Higgs boson.

The main theme/ subject/ topic of the book is the discovery of the mass mechanism, the so-called Higgs-mechanism. This name is actually unfair as there were six people who independently came up with this idea ; namely: Robert Brout and Francois Englert; Peter Higgs; and Gerald Guralnik, C. R. Hagen, and Tom Kibble. However, only one of them; Peter Higgs drew attention to the fact that this mechanism contains a massive boson whose properties can be used for testing the validity of the theory. So I argue that the Higgs boson is fairly named.

The work of these six theorists led to the  discovery of how mass could appear in the old equations without destroying the solution to the infinity puzzle. The second part of the story was the discovery of the connection between weak and electromagnetic interactions, namely the Weinberg-Salam model, whose basic SU2XU1 features were actually discovered by Sheldon Glashow, John Ward and Abdus Salam. Thus, four people were involved in the coupling of the two forces, only three of whom shared the Nobel Prize.

Glashow was the first to discover the so-called SU(2)xU(1) mechanism for bringing these two forces together mathematically.  Three years later, Salam and Ward also came up with this idea. it was not before 1967.. that Salam, independently of Ward, and Weinberg used the so called Higgs mass mechanism to show that if this mass mechanism was included in the underlying SU2xU1 structure a viable theory emerged. This was  finally proved by 't Hooft and Veltman.

This is the story of this adventure. It took a long time for the ideas to gain acceptance; when the first papers were produced in the late ‘60s very few people noticed them. It wasn’t until 1971 when 't Hooft and Veltman proved that this was a viable theory that an explosion of interest took place. The missing ingredient was to test if the theory really showed how nature works and to do that you had to find this boson and because it was so massive it took as half a century before it was possible to do experiments that were able to produce it and identify it and this is where we are now.

 

Is there a lesson for the theorists’ community to be learnt from this adventure?

I think that the story of the infinity puzzle provides a remarkable example of how one can find the right equations that describe nature.

As I often say in my lectures (to quote myself), it is easier to be Beethoven or Shakespeare than a theoretical physicist. If a few notes are changed in a Beethoven symphony or a few words in a Shakespeare play it is still a wonderful piece of art but if a couple of symbols are changed in a mass mechanism then it simply does not work. You can write beautiful theory but if it is not confirmed by the experimental data, then it means that this is not how nature works. It took 49 years to prove that this is how nature works. CERN issued the announcement of the Higgs boson discovery on 4th July That was the moment that the idea became reality.  The human intellect has the amazing ability to conceive theories, articulate them mathematically and then conduct experiments in order to prove them. Sometimes physicists are so near to it that we don’t realize the full importance of what we are doing.

When you decided to write your book were you afraid that you might hit a ground that was saturated by many other books and texts? What was the different perspective that you tried to adopt?

I wrote this book partly to educate myself, to learn in detail what exactly happened and how. I have spent my entire career working on quarks, gluons and strong interactions. Thus, writing books or popular science articles is a way for me to teach myself and explaining a subject to the public Helps me fully understand it

At the same time, I felt that there was this large movement from building the LHC, to discovering the Higgs boson and I wasn’t aware of any serious popularization to explain what this really is. There were many nice examples given by analogy (politician moving through a crowd of party workers and so on) but I was wanted a serious pedagogic exposition of the whole idea.

Perhaps, it should be mentioned that about ten years ago I wrote a book called “Lucifer’s Legacy” which was about Symmetry and Asymmetry. It explored how Symmetry can change from one form to another because that is the idea that was used by the Gang of Six. At that time I thought that I should not start discussing the Higgs boson. It was more important to talk about things that people are more familiar with. Thus, that book answered questions like: “What is symmetry and asymmetry?” “Why there are more right-handed people than left-handed?” “Why is our DNA folding one way or the other?” why when water freezes and turns to a snowflake a new pattern emerges although the basic laws of water molecules don’t care about direction when it freezes you can a six-fold symmetry so the underlying rotational symmetry has been hidden. There are many examples pointing to an underlying symmetry that cannot be seen n the big structures.

I went through that saga and ended up with some ideas about the Higgs boson. ”infinity puzzle” was my first attempt to discuss the Higgs. I talked with many people who were involved in the discovery and sometimes their memories of important events proved to be quite controversial. Hence, written records were very important. In the beginning of the book I use a quotation from Shakespeare's Henry V: “Old men forget. . . . But he’ll remember with advantages the deeds he does today” and he meant that many years after a great event you will see yourself as the centre of an action and talking to historians. Basically, the message was that diaries or written records are much more important than memories. For instance, I remember that when the J/ψ was discovered in 1974 I was here at CERN and I was recording interviews with various people, asking them about the importance of the discovery as it was clear that it was very important. However after a few years I lost the tape and I found it twenty years later as I was moving house in the UK. When I played the tape I was astonished because what I said on the tape was not at all my memory of events. It was as if someone has changed what was on the tape. The discovery of J/ψ was a tremendously important event for physicists and one would think that his memory of events would never change but it did. So at the end of the book I refer to this particular experience because I know that there will be people who will genuinely insist that what I have written is not what happened. However, if people discover further documentation that either clarifies certain issues or shows that the stories I present are not correct then I would be happy to make changes in a newest edition.

Are you feeling more fascinated by history?

Yes, probably because I am getting older. I have been lucky to have my professional physics career during a period that has been very exciting.When I started my career in physics there was a notion that the big discoveries had been made and it would not be possible to continue research on particle physics because of the enormous cost of the accelerators. But in my generation the discoveries of the charm, the W and Z, the top quark, the Standard Model, even the quarks themselves were made and I was lucky to be around and experience these events. Imagine that younger generations in forty years’ time will teach the next generation students’ things that might be discovered next year and we do not know yet what they are. Being part of it and see things moving from hypothesis to experimental tests and then to textbooks and becoming knowledge is very exciting and I wanted to share this experience.

Your book on Neutrinos has recently been published and I know that you are currently working on a second book on Bruno Pontecorvo. How did you decide to write the story of neutrinos?

In some ways this book was a slight accident. In 2005 I was asked to write an obituary for Ray Davis who won the Nobel Prize for his work on Neutrinos. His life and career, spending 40 years trying to set up an experiment that was considered impossible, was a fascinating story. Surprisingly, this obituary was awarded the prize for the Best Scientific article in a non-scientific context in Britain. That was very flattering and then I thought that since Ray’s story was so fascinating to try develop that into a small book that is how the book “Neutrino” came out.

In the course of researching I discovered what many writers find out; you start writing thinking that you know what to do but along the way you discover things that you weren’t aware of and your direction changes slightly. So although the central story line is about Ray Davisthere is also the question why John Bahcall didn’t share the Nobel prize with Ray Davis since he had been working with him for more than forty years. However, the unexpected thing was the role of Bruno Pontecorvo, the person behind the theoretical ideas. He went to the Soviet Union in 1950, in the height of the Cold War, for reasons that were never fully explained, as there has been a lot of controversy on this matter. Undoubtedly, his moving there played a role on him not getting a Nobel Prize. He thought up the idea that there are two varieties of neutrinos and he also designed the experiments that could test and prove this but he had to come somewhere like CERN to conduct that experiment and he was refused permission to leave the Soviet Union:  that was the nature of the game in those days. He wrote an article in Russian and it was published in a Russian journal but we did not  read Russian journals at that time. Unfortunately, by the time the English translations appeared, a few years later, the same idea has been developed in the U.S and it led to the experiment that was done by Steinberger, Lederman and Schwartz who shared the Nobel Prize for that. Pontecorvo started his life as an experimentalist although theorists know him for his contribution in theory. I became fascinated by him and he was one of the unexpected heroes of my book Thus, I decided that I wanted to write a biography on Bruno Pontecorvo on which I am working over the last couple of years. It is now 50% done and my goal is to complete it by the end of this year. It has been a fascinating adventure in which I met many interesting people, school-friends of his son who was twelve at the time when they left the UK – and then they disappeared for 5 years. I actually live in the same town that he lived and there are still people who remember him. It is a fascinating human story. The book is called: ”A life of two halves”. It is about Bruno as a scientist but also Bruno as a person who influenced many people; it is also about the people who knew him and how they reacted to his departure. Trying to find the reason for his sudden departure I used the Freedom of Information Act in the U.K to access some papers that still existed but had not been released. Then, I was told that some papers related to my request had been found. I have read these documents and now I know why they took the decision to move from the West to the Soviet Union so suddenly.

 Do the recent results from the LHC add more questions rather than giving answers to our fundamental questions?

I think the answer is yes. I think is reasonable to assume that we have discovered the way the fundamental particles gain their masses which gives rise to structure. However, the question why is the neutron is heavier the proton is not answered yet. If we examine the pattern of quark masses there are quarks with charges 2/3 like the top quark which is heavier than the -1/3 bottom quark and the charm quark is heavier than the strange quark yet for the -1/3 down is heavier than the 2/3 up - so they are the other way round. This means that the proton is lighter than the neutron, a fact that enables us to have hydrogen and other chemical elements. If the neutron was lightest then we would not be here. The fact that the electron's mass is conveniently capable of allowing it to be produced in radio-active decays and transmutations is again critical. It is important that we understand how they are getting their masses as we do not yet know why they have the specific masses that are observed. This raises another level of questions such as: “are the masses of these particles fundamental numbers that can be explained by a theory or are they accidental?” If we go back a few hundred years the distance of each planet from the sun was thought to be fundamental. Today we know that they are not fundamental but they have these distances by "accident" because of very complicated processes. The planetary orbits are accidental and they could be in totally different orbits. In that case probably we would not be here. Is that also the case for particle masses? Those who believe in the multiverse would probably argue that particle masses are accidental and they may have different values elsewhere while we just happened to be where their values are convenient. I don’t know whether these questions are philosophical or scientific. To qualify as science they have to be testable, at least in principle.Testing ideas about universes other than our own sounds to me a contradiction. If you can measure something, by definition it is in our universe. If it’s in some other universe, then its beyond our reach.