Gerald Guralnik

Gerald Guralnik

Name: Gerald Guralnik

Title: Chancellor’s Professor of Physics

Current institution: Brown University

Home state: Iowa

Alma mater: MIT, Harvard University

Reason for studying physics: I didn't always plan on becoming a physicist. When I went to MIT, I thought perhaps I would be a chemist. I ended up as a physicist. When I went to Harvard, I thought I was going to be an experimentalist. Somehow, I ended up as a theorist. I found the theory lectures mesmerizing, and I got hooked.

Paper published related to the theory of mass-giving mechanism: Global Conservation Laws and Massless Particles (Physical Review Letters, published November 1964, co-authored with Carl Hagen and Tom Kibble)

Contribution to theory: Carl Hagen and I have been good friends since our undergraduate years. After graduate school, I won a National Science Foundation fellowship and went to the Imperial College London, where I met Kibble. It was a natural combination for all of us to talk over the problem I first tackled for my graduate thesis (the problem of symmetry breaking and zero mass). The Goldstone theorem says that a field demonstrating spontaneously broken symmetry will cause the vacuum (the space in which it exists) to vary. That requires a new particle, which must be massless, to appear. This is a problem if this method is to be used to explain physical particles because the only observed massless particle is the photon.

In my Ph.D thesis, I showed that it is possible to have a theory where the photon is massless because of symmetry breaking. This was very interesting because in the usual theory it had been claimed that there is no reason for the photon to massless except the special case of small coupling. After my success with the new theory I tried to find a way to apply the Goldstone theorem to prove that claim was incorrect and that the photon was massless for any strength coupling. While I initially got it wrong, it turned out that the original claim is correct and that the Goldstone theorem does not require physical zero mass states in standard gauge theories—this was very important. My first Physical Review letter had most of this correct but made a subtle error which stopped me from reaching the correct overall conclusion.

Working with a modified version of the results of this first paper, Hagen, Kibble and I were then able to prove that the theorem was irrelevant for gauge theories (now known as the Higgs mechanism and not proven in any other of the relevant papers) and provided an explicit example of symmetry breaking without Goldstone bosons. The example necessitated a physical excitation of the field. This is what is now called the Higgs boson. Our paper was the only one to address the unwanted massless particle.

What were some obstacles you faced developing your theory? Spontaneous symmetry breaking in field theory was not widely accepted, even as a possibility, in the physics community at that point. I also made two mistakes in two separate papers published before the paper with Hagen and Kibble. That ended up being a good thing, though, since it was understanding those errors that finally led us to the discovery of this mechanism and boson.

How was the paper received in the scientific community? I gave talks in Britain and Europe, but the general reaction was marginally polite. I was told to stop working on the problems if I wanted to continue my career as a physicist. So, I did. I didn’t give a talk on this paper at all until the very late 1990s, maybe even early 2000.

What did you think about the July 4, 2012, announcement made at CERN about a newly discovered particle that looked a lot like the Higgs boson? I thought it might be coming—people had pretty strong suspicions. I had no intention of going to CERN for this announcement because I doubted that the data was very strong at the time, but the experimentalists working at Brown said I should go. I said no, but they told me I was going, and I have found that I should not argue with experimentalists.

I was surprised, pleasantly so, by how good and sharp the signals were for both CMS and ATLAS. I really didn’t think it was going to happen so soon and still had a fear that it might not happen at all.

What are you up to now? Mostly, I’m talking about the Higgs! I can’t believe how long it’s been since we published our paper. Who’d think I would start getting calls about this problem that’s 50 years old? I stopped thinking about the Higgs in the late 1960s, shifting my attention to other problems. I went more mainstream. Now, I’m very interested in chaos theory as it relates to particle physics, and I’ve developed a hobby of sorts with neuroscience. I’m working with people at Brown on cognitive science, because the brain is an interesting nonlinear system. Those two areas take up most of my time. Being able to work as a theoretical physicist at my age is a great privilege.