IPMU Interview with David J. Gross Interviewer: Hirosi Ooguri Elementary particle physics interested in science in general, was a goldmine in the 1960’s in particular in such an esoteric but theorists were powerless subject as elementary particle Ooguri: You have established physics. When did you decide the current paradigm of you want to be a physicist? elementary particle physics Gross: Long before I knew by discovering asymptotic what it really meant. I decided freedom, for which you were I wanted to be a theoretical awarded the Nobel Prize, physicist roughly at the age of and you have also made 13 or 14. great contributions to more Ooguri: That is pretty early. Not prospective areas of particle many people at that age know physics such as string theory. such a subject even exists. In addition to your scientic Gross: I did not really know achievements, over the past what it meant to be a 10 years or so as the Director theoretical physicist, but I was of KITP, you have transformed inspired mostly by reading this place into the center of popular science books, such as theoretical physics in the world. the ones by George Gamov. So, we have many things to What excited me was that you learn from you, especially as could gure out how the real we try to establish this new world works and solve the institute in Japan. It is an honor puzzles of the universe just to talk to you today. using your mind. That seemed I would like to start out by so exciting that I decided to asking when you became become a theorist and try to calculate the properties of the David J. Gross is Frederick W. Gluck world. I was very lucky since so Professor of Theoretical Physics many people are unsure exactly and Director of Kavli Institute for Theoretical Physics (KITP) at the what they want to do until University of California, Santa later in life. Barbara. He was awarded the 2004 Nobel Prize in Physics with David Ooguri: Then, you went to Politzer and Frank Wilczek for“ the Berkeley as a graduate student, discovery of asymptotic freedom in the theory of the strong interaction.” which at that time was“ the Among many other distinguished place” in particle physics. awards, he received the Dirac Medal in 1988 and France’s highest Gross: There were some great scientic honor, the Grande Médaille theorists in Berkeley at that D'Or from the French Academy of Sciences in 2004. time, and it was certainly the 16 IPMU News No. 8 January 2010 IPMU Interview center of the experimental fashioned way of teaching. We particle physics. At that time, teach our students the same with David J. Gross elementary particle physics was way a master artist will teach a true goldmine, a host of new an apprentice by bringing Interviewer: Hirosi Ooguri particles were being him into his workshop and discovered every month and having him participate in his it was not hard to discover creation of works of art. Not new particles and new all students are able to engage phenomena. It was a very in research immediately, but exciting time experimentally, the best students from a and experimentalists were place like Princeton or other the masters of the eld. The great research universities are theorists were pretty powerless. certainly able to start doing Ooguri: But your enthusiasm science from an early stage. towards theoretical physics was Ooguri: When you moved from not diminished. Berkeley to the East Gross: No, because there were Coast, you also so many problems. It was clear changed the that almost everything was not direction of understood, and the little your research. understanding one had seemed Gross: Berkeley ad hoc and paradoxical. It was was dominated by my exciting that constantly new advisor, Geoffrey Chew, things were discovered that who had this idea of the changed the way people looked bootstrap – a theory without at elementary particle physics. a theory. This was a very Ooguri: After graduating from anti-“eld theory” approach, Berkeley, you went to Harvard which said that elds cannot and then to Princeton, where be measured, are unphysical, you had great success with and one should not construct graduate students also. a dynamical theory in terms Gross: Well, it is easy to have of unobservable elds. Rather great success with graduate one should only postulate the students when you are at a general principles that constrain place which has many great the S-matrix, which was students. Frank Wilczek (Nobel observable. The hypothesis was Prize winner) was my rst that there was only one unique graduate student, and I think S-Matrix consistent with these Ed Witten (Fields medalist) must general principles. I got quite have been my third or fourth. I tired of this approach even Interview thought that was the norm. before I left Berkeley because One of the interesting things you could not do very much about science and mathematics with it. Moving to the East is that we still have a very old- coast was good because there eld theory was still tolerated. Hirosi Ooguri is a principal investigator of IPMU. He is also Ooguri: But, even in the East, Fred Kavli Professor of Theoretical eld theory was not yet the Physics at the California Institute of Technology. mainstream. there was no quantum eld Gross: In 1968 when string Planned to prove field theory I was ready when the useless, but discovered a theory that would describe theory was born, that was superstring revolution theory that works asymptotic scaling. a period where I was just happened in 1984 Gross: It was certainly not Ooguri: So, you set out to beginning to think about Gross: Well, to some extent, the mainstream, largely prove that eld theory was strong interactions and short but not totally. Remember because of its impotence. It useless and then instead you distances and deep inelastic that during those years there is essential for physicists to discovered a theory that works. scattering. At that time I was was a lot of development be able to calculate, to probe Gross: There were really three convinced that what one of supersymmetric theory, the limits of their theories parts of the program. The rst really needed for to describe which came out of string and to make predictions that was to show that you needed the strong interaction was theory originally. Everyone could falsify or conrm their asymptotic freedom to get the something totally revolutionary. in the eld was interested in ideas. Field theory at that time observed scaling. The next thing String theory was directly along supersymmetric theories by that was quite insufcient for the was to prove that there were that line of thought. time. At Princeton, Ed Witten strong interactions, since only no asymptotically free eld I got involved in string theory and I always had a continued perturbative techniques theories, which with Coleman quite early, but I also realized interest in string theory. John – Feynman diagrams – were I did, with the exception of that this was not going to Schwartz used to visit Princeton available for calculation. non-Abelian gauge theories. explain hadrons. I was focused once or twice a year because Ooguri: Then you discovered The last part of the program, on trying to understand what his mother lived there, and he asymptotic freedom and which I did with Frank Wilczek, was going on in short distances would always come and tell us changed the people’s was to look at non-Abelian inside the proton. One of the what was happening or give a perception about the gauge theories, which much nicest features of string theory seminar. usefulness of quantum eld to my surprise turned out to was the soft interactions, but So I was ready when theory as the language of be asymptotically free. It was those gave rise to very strong the superstring revolution elementary particle physics. almost one, two, three, QCD. falloff at large momentum, happened a year later, when Gross: The phenomenon of There was no choice. If you which was very different the Green-Schwarz anomaly asymptotic freedom was the wanted to explain the scaling, than what was seen in the cancellation was discovered. answer to the search for a you had to have a non-Abelian experiment – exponential as Suddenly, a lot of interest was theory that could explain why gauge theory. opposed to power falloff. So, generated. the strong interactions seemed Ooguri: After that, most of the string theory was not a good Ooguri: That led to your to behave as if they were free community moved to quantum place to try to understand the construction of the heterotic at short distances. It led to QCD, eld theory. simple scaling behavior at short string theory. the theory of the strong force. Gross: Well, because you could distances, and I stopped doing Gross: Well, it was the But more generally, having a calculate and furthermore, string theory at that point. But unexpected answer to an theory that was totally well even better, the calculations I continued to follow it even obvious question – how to behaved and under control in worked. And then there were through its darkest days. It was realize E8 x E8. And the answer the ultraviolet gave enormous some spectacular experimental always fascinating. was not so hard, once one calculation ability and resolved conrmations over the years. In 1983, I went off for a realizes that one could treat a lot of the lingering doubts But for me the major problem sabbatical to Paris and decided right and left moving waves about quantum eld due to its was not so much continuing that this was a good time to on the string differently.