John Schwarz recalls the long history of string theory

John Schwarz was just a young PhD fresh out of UC Berkeley, back in the days of draft-card burning and sad send-offs to Vietnam, when string theory began as a field. When the particle physics fervor over string theory as a way to describe protons and neutrons abated, Schwarz and small crew who remained saw the possibility of describing quantum gravity using strings and stuck with the subject, weathering career slowdowns and barbed comments along the way. Today he is the Harold Brown Professor of Theoretical Physics at Caltech.

You started working on string theory many years ago, when it was treated with scepticism (at best) by most of your peers and role models in physics. Were you ever tempted to give up and go work on more conventionally accepted and supported theoretical physics?
I was never tempted to work on something else because I was convinced that what I was doing was the right thing to be doing. So I kept at it. I obviously would have preferred had there been more widespread acceptance of what I was doing earlier but the fact that there wasn't didn't influence me to consider doing something else.

After the anomaly cancellation calculation in 1984, your whole life changed. String theory became a mainstream research topic, you were made a tenured professor, and the string community began to thrive. Why did things change so rapidly after that one calculation?
That came as quite a surprise to me because for several years prior to that, I had, we had made various discoveries that we thought would convince people that what we were doing was worthwhile, we being me and Michael Green, there was very little reaction to our previous results, so with that experience behind me, when we did the anomaly cancellation calculation, by that time I didn't really expect a dramatic response anymore. The thing that was different this time, though, was that very early on, Witten got wind of what we were up to and phoned me up asking for an early copy of our paper which I Fedexed to him. This was before the days of electronic communication and so I'm told that the next day everybody in Princeton university and the Institute for Advanced Study was studying this paper. After that things went very fast with the heterotic string and other things being done by people.

How much has string theory grown since it began in terms of the number of papers being written and the number of people working in the field?
String theory has had various ebbs and flows through time. In the early years, being the late 1960's, early 1970's, it was a quite active area of research - a couple hundred people working on it, each producing a few papers per year, but then it went very much into decline and there were just a few people working on it for a long period of time, and then, following this anomaly cancellation that we were just discussing a large number of people started working on the subject, several hundred, it's hard to be very precise and after that there have been somewhere between fifty and a hundred papers per month I would say. In the last few years things have been moving along really well and its probably as active now as it's ever been. One piece of evidence for the popularity of the subject is the attendance of various conferences. Each year there's a string theory conference and so for example, "Strings `95" at USC, there were perhaps 150 participants where as "Strings `97" in Amsterdam this past summer there were over 300.

What is currently the best hope on the horizon for finding some experimental support for the predictions of string theory?
Well, it's difficult to think of the experiments that could be easily performed that would test the ideas that we're proposing. Well, one very nice possibility is supersymmetry. This is a symmetry in the theory that predicts for every particle there should be a partner particle, and none of the supersymmetry partner particles has yet been discovered, but if our ideas are roughly right then we should be getting very close to discovering some of these and there seems to be a reasonable chance that one or more of them might turn up at the currently operating accelerators either in CERN in Switzerland or at Fermilab lab outside of Chicago, but if these accelerators fail to find supersymmetry particles then there's a very good chance they'll be found at the next large collider to be built, which is one that will be completed in CERN in the year 2005.