"Art is not merely an imitation of nature. Art is about creation. Art is creating the world. For the Arts, Nature is a nebula and the true challenge is to create its stars." 

G.Seferis, 1926

Earlier this autumn, George Zweig, father of Aces, visited CERN to give a Colloquium titled "Concrete Quarks; the Beginning of the End". An enigmatic title, like Aces, of which there are four in a deck of cards, but only three in the CERN Reports Zweig introduced early in 1964, while working as a visitor in the Theory Group at CERN. More on this below.

Following his work in the field of high energy particle physics, work that eventually led to the quark-parton model, Zweig moved to a totally different field, neurobiology, first doing experiments to understand how sound is represented in the auditory cortex of cat, and then retreating to the more manageable problem of characterizing cochlear mechanics He wanted to work in a field where ``how to think was not understood". George Zweig seems to represent the ideal of the Renaissance Man; after all he grew up in a culturally stimulating environment, confronting, while still very young, the big questions that were raised following the structural transformations and scientific discoveries that marked the second half of the 20th century. Discussions with George can easily move from new particle physics to the fresco's of a 15th century chapel in Sienna or open questions in theology. George Zweig has many interesting stories to tell, from the years in Caltech up to his recent work in the financial sector, while you will notice his excitement at learning new things, as he kept asking questions about the facilities here at CERN and how modern experiments are organized, the technologies developed and the physics questions at hand. What impressed me the most about George is his ability to be a good listener; carefully listening to the speaker and giving some time for thought before coming back with his response. I feel that George is a poet with the original meaning of the word, an artist who took the challenge and was lucky to see how a star is born out of a nebula.

I would like to thank him for this interview and the warm encounter. Moreover, I would like to thank Sonia Cabana, Despina Hatzifotiadou and Antonis Papanestis as well as the ALICE and LHCb secretariats for arranging our visit to the two experiments.

You can read George Zweig's talk "Concrete Quarks: The Beginning of the End" by clicking here 

PC: Tell us about your background.

GZ: I was born in Moscow in 1937. My parents moved to the USSR from Germany early in 1933, after Hitler’s inauguration as chancellor. My father was a structural engineer. It was the middle of the Great Depression, but he managed to get a five-year contract with the Russian government to help them prepare for a war with Germany, that he saw as inevitable. When his contract expired we moved to Vienna hoping to convince my father’s parents to leave Europe for America. Shortly after the Anschluss, when Hitler marched into Vienna in March of 1938, my father, mother, and I immigrated to the United States, settling in Detroit. We were able to enter the US only after the personal intervention of the two senators from the state of Michigan, Vandenberg and Brown. Despite their efforts, the US State Department would not admit my father’s parents, and they were shipped to Riga Latvia on January 26, 1942, with prisoner numbers 869 and 870, where they were murdered by the Nazis.

PC: I’m very sorry. …. Was your first degree in physics?

GZ: No, it was in mathematics, but as an undergraduate I also took many physics courses.

PC: Why didn’t you think of becoming an engineer?  Wouldn't this have been a safer career step?

GZ: No, the concept of a “safer career step” simply didn’t exist in my family. If you want safety, don’t get born. My mother’s family, who had lived in Poland, lost everything twice, once in the 1^st World War when they fled west, and once in the 2^nd World War when they fled east. I learned that everything you have of value is in your head, and you should use it to live a principled life. Survival yes, but worrying about a ``safer career step?’’ That wasn’t the way to think.

My father grew up in Vienna, and as a child witnessed the destruction of the Austrian-Hungarian Empire. After World War I only bureaucrats remained, with nothing left to govern. His generation wanted to create a new society to replace the one that had just collapsed. He joined a group of idealists that planned to leave anti-Semitic Europe for Palestine. He wanted to become a doctor, but since his friends thought there would be enough doctors, he was asked to become an engineer.

Let me tell you a little story that provides insight into his character and abilities. One afternoon as I was helping him organize papers in his desk, I found his graduation diploma in Structural Engineering from the Technische Universität Wien. Going further, I found a second diploma with essentially the same graduation date, but in Art History from Universität Wien. He had worked his way simultaneously through two colleges and never told me about it. When I asked him why he majored in these two different subjects in two different schools, at the same time, he said that others chose his profession for him, but he was interested in Art History.

He designed many factories for the war effort both in the USSR and the US, including one for the B-24 bomber whose assembly line was over one mile long and produced one B-24 per hour.

I eventually did became an electrical engineer, at least for a while, developing algorithms in the early 1970s for stimulating multi-electrode cochlear implants, and in the early 1980s for hunting submarines. Both algorithms were informed by a better understanding of how the cochlea processes sound, the problem that interested me most at the time.

PC: Did you feel comfortable in both the fields of physics and mathematics?

GZ: I felt more comfortable with physics. Mathematics in the US was taught in a very formal manner. I learned algebra from a wonderful algebraist, Jack McLaughlin, but the textbook we used was Jacobson’s two-volume set, “Lectures in Abstract Algebra,” and abstract it was! It seemed like there were as many definitions as results, and it was impossible to see how Mr Jacobson actually thought. The process was hidden, only polished proofs were presented. Later in graduate school I discovered some of what the Russian mathematicians were up to, and I felt at home with their style. For example Vilenkin’s “Special Functions and the Theory of Group Representations” was a real gem, fun to read, and helpful while applying Lie algebras to particle classification.  Books by Gelfand and Kolmogorov were also intelligible and interesting.

There was something about mathematics that I found enlightening, but also disappointing. As an undergraduate I took a course on the foundations of mathematics that discussed the problem of establishing the consistency of a set of axioms. In other words:  “If you have an axiomatic system, how do you know that all the axioms but one, can’t be used to prove that the other axiom is false?’’ My professor’s solution was to find a physical system where the undefined objects of the axiomatic system could be put into a one-to-one correspondence with objects in the physical system. If the axioms thus translated were true statements about the physical system, then since the physical system exists, the axiomatic system must be consistent.

What? Beautiful mathematics at the mercy of our grubby physical world! Of course more deeply, mathematics is a creation of the mind, and understanding its foundations must be connected with properties of the mind, and properties of the physical world, but to a naïve undergraduate it was a bit like finding out that Santa Claus does not exist. This revelation didn’t affect my decision to leave mathematics, but it made it apparent that in some respects physics comes first. If mathematics was more beautiful, physics was more interesting. It dealt with what was, or could be, fundamentally understandable.

Whether mathematics or physics, what I wanted in a primal sense was a way to understand the world to protect myself.  I had learned that Jews in Europe who did not see early on that the world was against them, or at best indifferent, perished. My mother’s father was an example of someone who saw reality; at the turn of the twentieth century, he founded the kibbutz Ramat Yishai in Palestine, and those that followed him survived.  Learning this, the rational route for me would have been to become an historian or political scientist, but I practiced a form of displacement, trying instead to understand what I found intelligible.

PC: How did you decide to work in the field of High Energy Physics?

GZ: I wanted to be a theoretical physicist, but didn’t know if I was smart enough. After all, smart people surrounded me, I mean really smart people like Richard Feynman and Murray Gell-Mann. These were heavy hitters. My peers, the theory graduate students, included Hung Cheng, Sidney Coleman, Roger Dashen, Jim Hartle, and Ken Wilson, to name a few. They were all remarkable in different ways. Why should I be able to cut it? I was of two minds. I didn’t think I could do it, but when I tried I felt a great sense of peace and satisfaction, much like a child lost to his toys. If I found something that was new to me, there was great excitement. It’s still that way now, but I have a lot less anxiety. I’m not as hard on myself.

PC: Weren’t you afraid to go into theory?

GZ: I could always fall back on experimental physics if I couldn’t make it as a theorist.  As a child I loved working with my hands. I built Tesla coils, bombs, and rockets, discovering by trial and error a rocket fuel of zinc dust mixed with sulphur. In grade school I was enrolled in the “industrial arts program”, not the “college preparatory program.” I disliked school, was absent a lot, and initially received poor grades.  When my grades improved and I was asked at the start of the 7^th grade if I wanted to switch to the college preparatory program, I asked what the difference would be, and was told that I would be able to take civics rather than shop. Lathes and milling machines seemed more interesting than civics lessons so I didn’t switch. I even chose to learn how to set type rather than learning how to type, a choice I eventually regretted. In college I ran the Millikan oil-drop experiment, but also found a way to use Brownian motion to accurately measure Avogadro’s number, since the charge on the electron was better known.

In graduate school my practical knowledge of tools was tested in an exam I had to take for the draft in downtown Los Angeles. I was shown a picture of a situation that required a tool, and then a second picture of several tools. I had to pick the most appropriate tool. For example, the first picture might be of a wet mess on a linoleum floor, and the second a picture of different types of mops, brushes, and brooms. There were many pairs of pictures. I have two recollections from that afternoon, first, standing naked in an enormous room with several hundred others waiting for a physical exam, and second, receiving the news, from a very surprised examiner, that I had a perfect test score (I didn’t have perfect SAT scores, unlike both my cousins. I guess schooling matters). Since I was registered with the draft in a poor Detroit neighbourhood where many less fortunate draftees were available, a letter from Carl Anderson, chairman of the Physics Department at Caltech, asking that my draft be deferred was easily granted.

I didn’t know what branch of theoretical physics to pursue. After my first year at Caltech, searching for summer work, I asked H.P. Robertson, the grand old man of general relativity, what I might work on. He said that general relativity was dead, but if I insisted, I could read Synge’s new book and then come back to talk to him about it.

Then I went to see Bob Christy, my quantum mechanics teacher, to ask for a problem. Disdainfully he replied: “You know nothing. Why don’t you go to the Synchrotron and learn experimental physics. If you do become a theorist you will find it useful. You won’t have time to learn it later on [1]’’.

PC: What did you do?

GZ: I went to the Synchrotron where Alvin Tollestrup was testing his fast electronics, which would be used to study non- leptonic K-decay at the Bevatron in Berkeley. I thought I could use the same beam for a different purpose, and proposed looking for a violation of time-reversal symmetry in leptonic K-decay, piggybacking on Alvin's experiment. If the μ in K_μ3 decay (K⁺ -> μ ⁺ + π⁰ + v) is polarised out of the plane of decay, the symmetry is violated.

Parity violation had been discovered only four years earlier and nobody had looked for a violation of time-reversal symmetry. I was hoping for a big effect, the same size as that found in parity violation. A measurement of the polarization of the μ was to be my thesis. The idea of users from other schools running experiments at the Bevatron was new, and we only had 21 successive half-days of machine time. After two years designing the beam, building the equipment, and running the experiment, a preliminary scan of spark chamber photos showed no effect.

PC: Did this result influence your decision to work in theory?

GZ: Absolutely! What to do? Spend two more tedious years determining errors and getting bounds, or pick a theory problem, and try to solve it. Exhausted and uncertain, I fled to Chichen Itza, in those days an isolated deserted Mayan ruin on the Yucatan peninsula. On returning I switched to theory.

However, the training I received working on the experiment with Ricardo Gomez building Caltech’s first spark chambers, and designing the K beam with Alvin, was invaluable. I ran computer programs tracking the phase space of particles in the K-beam; Alvin traced rays and floated wires. I watched these two think, and act under the most trying circumstances. Alvin was a remarkable experimentalist who never got the recognition he deserved. He designed the first superconducting magnets at Fermilab, and they worked! The design at Brookhaven failed catastrophically. Running an experiment also enabled me to judge the veracity of other experiments, an absolute necessity for the problem I was about to tackle.

Fortunately it only took me two years to learn these lessons. In the “good old days” the time would have been even shorter. Carl Anderson told me what life was like after he got his Ph.D. under Millikan in 1930. Dirac had proposed the existence of a partner to the electron, its antiparticle, and Carl wanted to find it by converting γ-rays found in the debris of cosmic rays into what we now call electron-positron pairs. He needs to get a big magnet, and build a cloud chamber with a lead plate and camera. When he asks Millikan for money, Millikan reaches into his pocket and gives him some. Carl goes to a couple of junk shops for supplies and gets to work. When the magnet, cloud chamber, and camera are finished, Carl puts them, together with food and a sleeping bag, into his old Model T Ford, and drives up the unpaved Mount Wilson Observatory road into the San Gabriel Mountains behind Pasadena. Carl is on his way to discovering the positron.

PC: What did it feel like when the experiment was over?

GZ: Terrible and disorienting. After having spent two frantic years building and testing equipment, one morning, unexpectedly, an overhead crane comes rumbling by, tearing everything apart. Time for the next experiment! I took it personally. Others only wanted answers to abstract questions, but the spark chambers, scintillators, counters, cables, and the concrete blocks that shielded us were embedded in my being, and now were being torn apart.

PC: Was there an atmosphere of disappointment that we would be lost forever in the zoo of particles?

GZ: Not at all! It was very exciting. I remember waiting with great anticipation for each issue of the Physical Review Letters. On the other hand, Willis Lamb, in the first paragraph of his 1955 Nobel Prize Lecture, joked that he had ``heard it said that `the finder of a new elementary particle used to be rewarded by a Nobel Prize, but such a discovery now ought to be punished by a $10,000 fine.' " That was the older generation talking.

PC:   How did you finally start your PhD in theoretical physics?

GZ:  I needed a thesis advisor and there weren’t many choices. Fred Zachariasen didn’t like students. Steve Frautschi was approachable, but worked on the bootstrap. Feynman wasn’t taking students. In fact, I found out later that Feynman insisted on two conditions before coming to Caltech from Cornell, that he be allowed to take a sabbatical in Rio since he was due a sabbatical from Cornell, and that he not be required to supervise graduate students writing theses.

However, Murray Gell-Mann had many students, and his students graduated quickly, so Murray was the natural choice. Alvin had suggested that I talk to Murray about Alvin’s experiment, and I had seen Murray on several occasions to discuss K decay. So after returning from Mexico I asked Murray if he would be my thesis advisor. He said ``No!’’ He was leaving on sabbatical, but said that he ``would talk to Dick.” Dick was Richard Feynman. I had just started sitting in on Feynman’s gravity course, so he might have known my face, but nothing more.

About a week later I very sheepishly asked Feynman if he would be my thesis advisor. He responded: “Murray says you're OK, so you must be OK.” Every Thursday we discussed physics from 1:30 in the afternoon till tea time at 4:15. I prepared frantically for each meeting. We never talked about a topic twice. One afternoon I told him that I wanted to tell him about my thesis, which was finally finished.  Enthusiastically but formally he said “Very good, very good.” When the afternoon was over I had his approval. But when he read the written version, he was very unhappy.  The thesis was essentially two papers, in two very different areas, stapled together. Feynman said that a thesis was not a paper or papers to be published, but a document for others at your school to read. It should state in simple terms what problem was solved, why it is important, and how the solution was obtained. So I wrote a nontechnical preface indicating the interest and significance of the problems, and that seemed to satisfy him.

PC: How did you come up with the idea of quarks as concrete objects out of which hadrons are made?

GZ: There was a remarkable problem that required a solution, although the existence of this problem was not widely recognized. The φ meson wasn’t decaying into ρ+π, which should have been its dominant mode of decay. Instead it was decaying into the kinematically unfavored K+ K̄ mode. This suppression of ρ+π, by two orders of magnitude, had to be dynamical, since a symmetry for suppression was not available. I was transfixed by this problem, and discussed it with Feynman in the spring of 1963, and two or three times thereafter.

Viewing mesons as composite objects, that I called aces, provided a solution, if mesons contained aces with the proper quantum numbers, and if the aces in a decaying meson were conserved, that is, became constituents of the decay products. Since aces in the φ where not present in the ρ or π, the reaction φ -> ρ + π was forbidden. But crucially, the composite assignments necessary to forbid the decay also gave rise to two mass formulae for the four vector mesons that were satisfied with remarkable accuracy, so I was killing ``three birds with one stone,’’ making the argument more believable.

PC: What was Feynman’s reaction?

He thought the experiment must be wrong because it was not consistent with unitarity, a cornerstone of hadronic physics. Unitarity mixed all states with the same quantum numbers, so it didn’t make sense to distinguish K+ K̄ from ρ+π, since their quantum numbers are identical. I didn’t listen to him and kept exploring this idea in the spring of 1963.

Feynman was sure the rule for decay involving aces was fatally flawed for the same reason. He viewed it as a bizarre solution to a problem that didn’t exist, and both the experimental observation and its interpretation were inconsistent with unitarity. This view was perfectly sensible. He understood that if φ -> ρ + π was forbidden, something would be terribly wrong with our understanding of the strong interactions. He was right; something was terribly wrong.

PC: Was it hard going against the Master?

GZ: It was, especially because I had ignored his advice before, and that turned out to be a big mistake. It was the fall of 1962. Gell-Mann and Ne’eman had proposed that the strongly interacting particles be classified in representations of SU(3). On one of our first Thursday afternoons I suggested that the weak currents of the strongly interacting particles also be classified in representations of SU(3), and that both the 8 and 27 dimensional representations be used. The 27 representation was necessary because the decay Σ⁺ -> n + μ⁺ + v had just been observed in emulsion by Barkas and his collaborators (the change in strangeness in this decay had the opposite sign of the change in charge, i.e., ΔS/ΔQ= -1  an unprecedented occurrence that required the 27). Although there was only one example, called the ``Barkas event,” the event was exceptionally clean. Barkas was a very good experimentalist working with strong team using a well-understood technique (Powell had used emulsions to discover the pion 15 years earlier). The alternative possibility was that the dominant mode of decay, Σ⁺ -> n + π⁺  was followed very quickly by π⁺ -> μ⁺ + ν. However, the probability that this chain of decays would be confused with the direct reaction Σ⁺ -> n + μ⁺ + v , was 10^-7, and only about 100 Σ decays had been observed.

Feynman liked the idea of applying SU(3) to hadronic weak leptonic decay, but kept saying ``Throw away the 27!’’ When I insisted that the Barkas event couldn’t be ignored, he got angry and said the experiment must be wrong. I was paralysed, and rather than doing what he said, I set the idea aside. I didn’t want to blindly follow his advice, and I didn’t have the confidence in my abilities to let taste trump experiment, like Feynman did when he proposed the V-A theory of leptonic decay. Several months later I picked up the Physical Review Letters and read Nicola Cabibbo’s beautiful paper where he finessed the issue by only considering the 8-dimensional representation. Almost 40 years later I bumped into Nicola while he was visiting Los Alamos National Laboratory. I asked him if he hadn’t been worried about the Barkas event. He said: ``Yes, but I had an advantage over you because I was at CERN where they had observed another ten thousand Σ⁺ decays, and not one of them was Σ⁺ -> n + μ⁺ + v so I decided to publish.’’

PC: Why three aces if there are four aces in a deck of cards?

GZ: I didn’t know how many aces there were. Aces were represented graphically as regular polygons of increasing size, corresponding to increasing mass. Aces were fundamental point particles like leptons, and like leptons they had fields that entered into the electromagnetic and weak currents. Therefore I guessed that the number of aces would equal the number of leptons. Since four leptons were known at the time, I called them aces. I should have called them dice.

PC: Were aces the same as constituent quarks?

GZ: No, concrete quarks were chimeric, a combination of constituent and current quarks. When used to construct the electromagnetic and weak currents, they were fields in a field theory, like current quarks. When used to compute masses and strong coupling constants, they were constituent quarks, objects whose precise definition still eludes us. They were never quarks in the sense of the naïve quark model, because no assumptions were made about their interactions. I only assumed the absence of three-body forces.

PC: Did you think that aces were real objects that could be experimentally observed?

GZ: I didn’t know, but aces had dynamics, so it was hard to believe that they weren’t real. They had mass, binding energy, spin, angular momentum, and L dot S couplings. In addition, aces in a hadron were conserved in decays. None of this would make any sense if aces weren’t real particles inside of hadrons.

PC: Did you try to publish a paper when you came up with this theory?

GZ: I wanted to send a paper to the Physical Review, but the head of the Theory Division, Leon Van Hove, wouldn’t allow it. He told me that all reports from CERN had to be published in European journals, even though American institutions paid my salary, overhead, and publication costs. When I asked the theory secretary, Madame Fabergé, to retype the paper for publication, she politely refused, saying that Van Hove had instructed her not to type any of my papers. This was a real problem because I didn’t know how to type, and didn’t have a typewriter (remember, I was trained as a typesetter, not a typist).

I was scheduled to give a theory seminar at CERN titled ``Dealer’s choice: Aces are Wild”. Van Hove cancelled the seminar, and I was not allowed to reschedule it. When Van Hove and Kokedee published a book four years later reprinting articles on the quark model they did not include either of the CERN reports. Van Hove deliberately and systematically tried to keep my work from public view.

PC: When did you first hear that quarks were confined?

GZ: I don’t remember. I do remember, when first thinking about mesons as ace-antiace pairs, wondering about the nature of the potential between them, wondering if the potential was infinitely deep, wondering if aces were bound. The pictures of hadrons in the two CERN reports always have aces connected to other aces by lines. Aces never stand alone.  That’s no accident. I was just representing what I knew to be true. Recently I was reminded of a question Feynman asked when I gave my first colloquium at Caltech after returning from CERN. ``What are those squiggly lines [between aces]?” he asked. ``Springs!’’  I answered. How strong were those springs? I had no idea. (The lines are squiggly in mesons and straight in baryons because it was too tedious to draw three squiggly lines for each baryon). I certainly hoped aces were free, and that we would find them. The first thing I did when returning to Caltech was recruit Ricardo and others to look for them in cosmic rays using the spark chambers left over from the K-decay experiment (PRL 18, 1002 (1967)).

After first hearing about confinement I remember telling my 10-year old son Geoffrey that free quarks cannot exist, at least according to current theory. Then I told him that ``In the beginning there was the quark-gluon plasma, and as the Universe expanded and cooled, clusters of three quarks condensed from the plasma to form protons and neutrons.’’ He immediately asked ``How do we know that the number of quarks in the Universe was divisible by three?’’ (laughs). I am afraid I still don’t know how to address that question.

PC: How do you see the development of High Energy Physics since your days in graduate school?

GZ: Locally exciting, but globally disappointing. I started graduate school in 1959, 50 years after the Geiger-Marsden alpha-particle scattering experiment that would eventually lead to the discovery of the nucleus. The advances in fundamental physics, and their applications, in those 50 years were phenomenal. Now it’s the 50^th anniversary of the discovery of aces, and comparatively little of excitement has happened since then, because of the paucity of experimental information, and the absence of applications. Although unlikely, incredible applications may still lie ahead. For example, if free fractionally charged particles exist, it should be possible to catalyse fusion at room temperature. (There is no known connection between color, which appears to be confined, and fractional charge.)

On a fundamental level, there is also disappointment. Newton’s laws are beautiful, Maxwell’s equations are fine, especially when written in terms of the vector potential, and quantum mechanics is wonderful. But the Standard Model is a mess. The first sign of trouble was Cabibbo’s angle, some small random number that appeared in June of 1963. It’s ugly as sin (actually Feynman thought of it first in the late 1950s, but never published). I fought hard to avoid using it, trying to find a dynamical explanation for the suppression of strangeness changing weak decays. The first part of my thesis addressed this problem. The CERN report a few months later attributed the weak decay of baryons to the weak decay of their aces, and showed that the observed strangeness-changing baryon leptonic-decay rates were still consistent with a weak current made from aces without the Cabibbo angle. Then came CP violation one year later with an even smaller number. We still haven’t recovered. On the other hand, there is a wonderful problem to solve. It’s so hard to compute these small parameters that any theory, which does, will surely be correct, or at least largely correct (Bohr computed the seemingly arbitrary Rydberg constant, but didn’t have all of quantum mechanics). For this we probably will need hints from new experiments.

PC: What are your thoughts about the future of High Energy Physics?

GZ: Since I haven’t worked in the field for over 40 years, my answer will have both the advantages and disadvantages of distance.

We don’t know enough to make real progress, and acquiring information is becoming increasingly expensive. In 1965 on a visit to Washington, D.C., I bumped into Peter Franken, a physics professor from the University of Michigan where I had been an undergraduate. He asked what field I had gone into, and when I told him he exclaimed “What, High Energy Physics? High Energy Physics is dead! It’s a line item in the budget.” Well, not quite. The death was not sudden, but it was a death nevertheless. Thank goodness for Europe.

There are encouraging signs for the future. Dark matter and dark energy exist, and have no explanation. The Standard Model, which does a lot of explaining, looks like an ugly kludge, and so needs fixing. In addition to the large number of free parameters, there are concerns that these parameters must have very special values for our Universe to exist, the so-called “naturalness problem.”

String theory suggests a solution, the existence of an enormous number of universes, each with different laws of physics, and ``explains” ours as one that can be observed because it has laws that enable our existence. An ``anthropic principle” is responsible for the special parameter values in the Standard Model.

Really? The solution to the naturalness problem is probably not so sensational. Perhaps our theoretical limitations are being elevated to a grand principle. Invoking the anthropic principle may be a symptom of limited progress in a very difficult field. The anthropic principle should be invoked only after all other avenues have been explored. This line of thinking inhibits investigation, and is therefore suspect. Our inability to go beyond the Standard Model may be directly related to limited experimental information. Current theory may be correct, but it is essential to experimentally explore much higher energies than are currently available. Who knows what will be found?

Rather than trying to understand new natural phenomena, theorists are reduced to asking whether they are happy with the theories they already have for the strong, electromagnetic, weak, and gravitational forces. These theories are consistent with all measurements ever made that have any bearing on these forces! It’s just that for them these theories are not pretty enough. The ``naturalness problem’’ and the ``hierarchy problem’’ may be self-inflicted wounds. It's fine to ask if your current theory looks like older theories, and is ``beautiful,’’ but it’s dangerous to substitute aesthetics for observation[2]. It’s human nature to work with what you’ve got, and theorists haven’t gotten what they need, information. If spectacular discoveries are not made at the LHC, High Energy Physics may end "Not with a bang, but a whimper." Novel, cheaper methods of particle acceleration are needed.

We have benefited from miracles. We do mathematics without having explicitly evolved that ability. The laws of classical and quantum mechanics have simple mathematical expression. Electricity and magnetism, and general relativity, have elegant mathematical formulations. But miracles might cease. Although we currently are limited by experiment, eventually we may become limited by our very nature in understanding the Universe. Why should we, with our machines, have evolved to fully understand it?  But in the meantime, let’s keep trying.

PC: Thank you.

GZ: You’re welcome.