Particle Physics


My Enchanted Evening

From A BEAUTIFUL QUESTION: Finding Nature’s Deep Design by Frank Wilczek. Reprinted by arrangement of Penguin Press, part of the Penguin Random House company. Copyright (c) 2015 by Frank Wilczek. Publication date July 14, 2015

Up until 10 PM or so, the day that would turn out to be the most productive in my scientific career seemed anything but promising. My very young daughter Amity had an ear infection, and all day long she was feverish, cranky, and needy. Betsy and I, inexperienced in parenting, newly arrived and on our own in Fermilab’s impromptu village, coped as best we could. As the dark midwestern night set in, Amity at last fell into exhausted sleep, and then Betsy too. They looked like angels of peace.

The alertness and energy that coping with a stream of little crises had called forth was still with me, after the crises themselves had passed. Seeking an outlet, I decided, as I often do, to take a walk. The night was brilliantly clear, the sky radiant, the horizon sharp and distant, and even the ground, moonlit, seemed ethereal. With images of earthly angels lingering within me, and celestial spectacle surrounding me, I felt an unlikely elation. It was a time for big thoughts.

Flickr user Michael Kötter, adapted under a Creative Commons license.

Over the preceding few years, theories of the strong, weak, and electromagnetic interactions based on local symmetry had matured from bold adventure to conventional wisdom. As I reviewed this situation, in my mind, it occurred to me that while the various quarks, leptons, gluons, and weakons—not to mention photons—had received a lot of attention, and were the focus of well thought-out experimental programs, the symmetry breaking was relatively unexplored.

A little story will set the stage:

On a water-covered planet in a galaxy far far away, fish have evolved to become intelligent—so intelligent, that some of them become physicists, and to study the ways things move. At first the fish-physicists would derive very complicated laws of motion, because (as we know) the motion of bodies through water is complicated. But one day a fish genius—Fish Newton—proposes that the basic laws of motion are much simpler and more beautiful: in fact, they are Newton’s Laws of Motion. She proposes that the observed motions look complicated due to the influence of a material—call it “water”—that fills the world. After a lot of work, the fish manage to confirm Fish Newton’s theory by isolating molecules of water.

According to the Higgs mechanism, we are like those fish. We are immersed in a cosmic ocean, which complicates the observed laws of physics.

Physicists had been invoking the Higgs mechanism for many years, and with its use have gone from success to success. Many aspects of the interactions of W and Z bosons, besides their masses, were predicted accurately by using the beautiful equations of massless particles and gauge symmetry, with their consequences suitably modified by a space-filling material. In this way, we built up a convincing case for the existence of our cosmic ocean. But ultimately that case rested on circumstantial evidence. There was no clear answer to an obvious question: What’s it made from?

No known substance could provide the cosmic ocean. No combination of the known quarks, leptons, gluons, or other particles has the right properties to make it. Something new was required.

But there wasn’t even a credible proposal to test the very simplest, “minimal” model, featuring a single Higgs particle. The basic problem is simple: the Higgs particle, in that model, likes to couple to heavy particles, but the particles of stable matter, that we can study directly or put into our accelerators, are very light. The color gluons have zero mass, as do photons, while the u and d quarks, and electrons, have negligible mass.

But recently (as of 1976) there had been a lot of interest in heavier quarks. The charmed quark c was a fairly recent discovery, and there were excellent reasons to suspect that two additional, still heavier kinds would also exist. (And they do. The bottom quark b was discovered not much later, in 1977, while the top quark t took until 1995. They had been named, and their properties—with the sole exception of their masses—had been calculated, even before their experimental observation.) So it was natural to consider whether new, heavier quarks could open a portal through which we’d get to the Higgs particle. I realized right away that they might. You can use the same tricks that people had used for charmed quarks, to produce produce mesons based on bb or tt. Those heavier quarks would couple vigorously to Higgs particles. If things broke right—basically, if the heavy quarks had more than half the mass of the Higgs particle—then Higgs particles would be produced in the decays of those mesons. That was my first important realization of the night.

Now it was important to consider how the Higgs particle decays, since its products might be indistinguishable from background, making the whole thing academic. One of the most important possibilities to consider is decay into color gluons. I couldn’t do an accurate calculation in my head, though it seemed OK, from rough estimates. (It is.) More importantly, this got me thinking: if the heavy quarks can couple to Higgs particles and to gluons, then they provide a way to connect gluons to Higgs particles! And at that moment, my brain had hatched the basic process you see in the bottom half of the figure below. Again, accurate calculation would be a chore, but I did some crude estimates in my head, and found the results encouraging. In particular, I realized that even if the missing quarks were very heavy, they’d still contribute—and that if there were even more, heavier quarks, they’d contribute too. It was clear to me, right away, that this was the dominant way Higgs particles would couple to stable matter, and a promising window into the unknown. That was my second important realization of the night.

At that point I’d reached the lab site, and I decided to turn back. I’d had good luck thinking about the minimal Higgs model, so I wanted to consider how the new ideas would apply to more complicated versions. The changes are easy to work out, for any given version, so I started considering what would be the most interesting complications to consider. An especially interesting possibility, is to have some extra symmetry, that gets broken spontaneously. This can lead to the existence of new massless particles—a spectacular possibility! That was my third important realization of the night.

This sketch depicts the process through which the Higgs particle was discovered experimentally. It is a tour de force, that puts many aspects of the Core, and deep principles of quantum theory, to work simultaneously. For a full explanation, see the text.

Back in Princeton, where I’d been teaching during the year, there’d been enormous excitement about something called instantons—which I won’t even try to explain here. Instantons break symmetry in particularly interesting ways, and I thought it would be fun to bring those in, so I’d have something to talk about, that my colleagues would be interested in hearing. I dimly perceived that the particle that would otherwise have been massless, according to my third realization, would instead get a tiny mass, and would have other interesting properties. That was my fourth important realization of the night, and brought me home.

Those four insights have had different fates. The first was a victim of bad luck. The b quark is not heavy enough, compared to the Higgs particle, while the t quark is so heavy and unstable that its mesons are useless.

The second is one of my proudest achievements. More than thirty years later, it was central to the actual discovery of the Higgs particle.

The third hasn’t borne fruit yet, but remains interesting. I eventually called the massless particles “familons,” and people continue to look for them.

The fourth turned out to be the most interesting, and possibly the most important. When I got back to the lab the next day, and consulted the literature on these things, I discovered a very interesting paper by Roberto Peccei and Helen Quinn. They’d looked at the kind of model I’d been playing with, and pointed out that it could solve a very important problem, the so-called θ problem. It would require a long digression to explain that problem here. The essence of it is, that there’s a number—θ—that the Core says could be anything between -π and π, but which is observed to be very very small. That’s either a coincidence, or an indication that the Core is incomplete. In Peccei and Quinn’s model, the “coincidence” got explained as the residue of a new (spontaneously broken) symmetry. Peccei and Quinn didn’t notice, however, that their model had a light particle in it! And so I got to name the thing. I had noticed, several years before, that there was a detergent, Axion, whose name sounded like a particle. I resolved that if got the chance, I’d make it so. Now the θ problem, along the way, involves an axial current. That gave me an opening, to sneak the name past the watchful, conservative editors of Physical Review Letters, which I did. (Steven Weinberg also noticed this new particle, independently. He’d been calling it the “higglet.” We agreed, deo gratias, to use axion.)

The axion has had a long, winding, and still unresolved history. It is a subject I’ve returned to many times, developing the theory of its production in the early universe, and suggesting the possible existence of an axion background, analogous to the famous microwave background. According to this work, the axion background will be difficult, but not impossible, to observe. A hardy band of brilliant experimentalists are actively searching. Some day soon, the axion may deserve a book of its own, for it has become a leading contender to provide the dark matter of the universe. Or it may not exist at all. Time will tell.

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Frank Wilczek

    Frank Wilczek has received many prizes for his work in physics, including the Nobel Prize of 2004 for work he did as a graduate student at Princeton University, when he was only 21 years old. He is known, among other things, for the discovery of asymptotic freedom, the development of quantum chromodynamics, the invention of axions, and the exploration of new kinds of quantum statistics. Frank is currently the Herman Feshbach professor of physics at MIT. His latest book is A BEAUTIFUL QUESTION: Finding Nature’s Deep Design.

    • I am inspired to research more into subatomics and this axion work, and am appreciative of your thoughtful reflection and imagination into the nature of reality. Science is and will continue to be the biggest driving force of the current age. I am excited to learn what else you may find!

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      If you test for a conveyance of light… you would test if there is one, correct?

      Michelson-Morley did NOT do that, they tested if the Earth was rushing through an Ether (medium), that is an erroneous constraint and a big mistake.

      Then everyone completely loses all sensibility and accepts the experiment as valid.

      That means (they think) light does not have a particle field it travels in and since it cannot be just a pure vibration or energy (since there are no such things) they have to invent a mass-less particle. That is compounding the mistake and it is 2 levels deep at the moment.

      But everyone knows matter does have mass.

      But this supposed massless particle does not. So, to explain it they come up with an Higgs field that is completely filling space (in the same way an ether would) and that is what is giving mass only to certain particles. Now the mistake is 3 levels deep.

      NOTE: The Higgs field would actually be a particle field. They think they found the Higgs by smashing protons together and getting the mass-energy?
      That is guess work. I have something the weighs 2 grams, what is it?

      The funny thing is they think photons are massless particles.
      Think about how many there would be.
      Space would be almost solid with massless particles all zipping around in every possible direction at the speed of light. That would mean space is actually filled with particles. And space is also filled with the Higgs particles.

      So, what happened is they thought they eliminated the one particle field that explained how light travels (the ether, medium) and now to explain light they need at least 2 particle fields.

      Einstein knew there was an ether but he went along with them because he knew they were all imbeciles, it’s actually really easy to see that.


      THINK ABOUT IT AGAIN: If there are massless particle photons, space is actually filled solid with them and they are zipping around at the speed of light.

      NOTE: A field actually has to be something, i.e. a particle field. It is NOT pure magic or nothing like a mainstream definition. “Filled solid” does not mean literally solid. Everyone knows nothing is actually solid, atoms are mostly empty space

      • Paul

        All fine except that you really haven’t worked out any of this with a real mathematical theory just like most armchair philosophers?

        • When idiots make a mistake, others compound on it and someone explains the whole thing… you think you can covert that into math?

          The world is loaded with imbeciles and you are part of the problem.

    • If you were going to test if there is a medium for the conveyance of light, would you…

      a) Test if the Earth is rushing through the medium.
      b) Test if there is a medium.

      Michelson-Morley “confirmed” there is no medium with their experiment.
      Here is your chance to agree with those great men and pick “a”, everything you think you know is based on that.

      NOTE FOR IMBECILES: The correct answer is of course “b” but modern physics is based on MM experiment and they picked “a”, Good luck with that!

      • David Eddy

        I would think there is a medium for conveyance of light that exists in space that
        makes it possible for far away stars to be seen from earth.

        I think I remember reading a paper that claimed that there is a medium that exist in the entire universe but that it has not been able to be quantified. I would think in order to have propulsion for space ships, it would be necessary to have a medium to push against in order to get forward thrust.

    • Jeanne Marie Bentsen

      What sky is he watching?…..The Military Industrial Complex and HAARP are controlling the jet stream and the weather. They are spraying us with aluminum, barium and strontium, lead and mercury. Chemical trails sprayed from planes. Look Up. The spraying is interfering with the normal activity of the sun. Trees and animal species are dying. Forests are burning up. Asthma, Alzheimers, and ADHD are on the rise. The elite (Illuminati…Agenda 21) have underground bunkers built, while we will have to face the ongoing global warming which they are making worse with their geo-engineering, as they say it is to cool the planet. They are making it worse. They want to reduce the population.The ice is melting to almost nothing in the Arctic as we speak. Methane gas is releasing into the atmosphere. They now want to rape the Arctic as they have with the rest of the planet. Let’s join in the fight. For more reliable info go to: