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#### Jim Gates, a supersymmetrist from superspace

Jim Gates came into particle physics at just the right time for his brave choice of a thesis project to assure him a place in the early development of supersymmetry, supergravity and superspace. He's been working to explore and understand superspace since the seventies. Gates received his B.A. and Ph.D. at MIT, and is currently the John S. Toll Professor in Physics at the University of Maryland.

When and how did you first become interested in physics and mathematics?
Well the answer to the question has, unfortunately, a number of parts. The first part is when I was about eight years old. My father brought home a book one day and it was about space travel. And in this book I learned that the stars in the sky were not just lights but places to go. And suddenly my universe got very much larger and I knew that science was the way, science and technology, the way to get to such places. So that was part one.
Then a little bit later we had a set of Encyclopedia Britannica and I was probably in the third grade, and I was bored one day, just thumbing through one of the volumes. And I came across Schrodingers Equation, and I was amazed. I knew it was mathematics because I saw an equal to sign. Then I saw a bunch of symbols, Greek letters and partial derivatives, which I had absolutely no idea of what it meant. It had some sort of strange attraction to me, because it was like looking at notes on bars for music, but not knowing how to read the music. So I felt some affinity and said, gee Id like one day to know what that thing means.
And then finally, the third part of it is that when I was a junior in high school, I actually took a course in physics, I was the only junior in the class. And a really good physics teacher. And at the beginning of the course he made the simple demonstration that if you let an object roll down an inclined plane and measure the time that it takes for it to roll down, you find the distance traveled is proportional to the square of the time.
Now for most people that doesnt mean anything, but for me this was actually an amazing demonstration, because I had always known that mathematics was essentially a game that we play inside our heads, and that you could make up the rules for mathematics just like you could make up the rules for anything else. And so by the time I was a junior, I was quite used to thinking of mathematics as something imaginary, not having anything to do with the world around us. And yet suddenly here was this teacher showing me that this crazy game that I knew how to play inside my head could describe the way things move in the world around me.
I never got over that experience. I immediately said thats what I want to do, because I know how to make up stuff real well, so if Im going to make up these mathematical games and some of them are actually going to be real, then what could be more fun?

What led you to decide to work as a theoretical physicist, doing supersymmetry and supergravity of all things?
Well, theoretical physicist, that part is simple. When I was a child, there were only two things that I could imagine doing that would be interesting when I grew up. One of them was to be an astronaut and I didnt quite make that one, but a very close friend of mine did. And the other option was to be a physicist. So by the time I got my Ph.D. it was clear that the latter of these two goals was actually something I could do in life. Theoretical because, for example, as an undergraduate I actually double-majored in both mathematics and physics, and math was sort of fun, but physics was actually just intensely interesting. So I always knew it would be some sort of career combining mathematics with physics that would be the goal that I would pursue.
Now supersymmetry and supergravity, well, that parts got a little bit of a story to it. When I was a graduate student looking around for a topic on which to do my Ph.D. thesis, I started by working on a problem in whats called weak interaction physics, and I had an advisor who taught me some various mathematical techniques and techniques of analysis and what have you. It was pretty quickly clear to me that these things could be mastered and that I had done so. But it was also pretty clear to me that if I was going to be successful in my career, I had to find a way to distinguish myself from all the other hundreds of young people I imagined also learning these same things.
So what I did was to make a survey of all of the literature in particle physics, this was probably around 1976, looking and classifying what were the major trends that I saw occurring in the field. And during this survey I came across one or two papers which contained some of the strangest mathematics I had ever seen used to describe physics. There were examples of symbols that were being used in ways that hadnt been used in any class. And as I read this material, it was an introduction to the notion of superspace and supersymmetry, and I immediately recognized that: a. It was new, nobody essentially knew anything about it, and b. It was the kind of mathematical physics where having insight into geometry and understanding some physics might actually get you a pretty far piece in making some progress.
So I decided then to change the direction of my research from weak interaction phenomenology, and I had a very understanding advisor who basically said go right ahead, Ill help you if I can when you get stuck trying to learn the material, but youre responsible for your own career. That was just fine with me.
So during, I guess it was my seventh and eighth year as a graduate student at MIT, I was the only person in the department that had any interest whatsoever in supersymmetry or supergravity. But by the time I had graduated I had essentially gotten to the forefront of the field, being that it was such a young and new area, and so I was able to actually make contributions in the field that had never actually occurred before. Which meant, as some friends observed, that I had become a worlds expert, which was pretty funny to me at the time.

How would you sell the idea of supersymmetry to the general public?
Well, first of all, I dont think you actually sell an idea like supersymmetry to the general public. The first thing I think thats truly important is to try to get the public to understand what it is that were proposing. Im one of those scientists that sort of feels that as scientists, we owe our public open reports on what it is that we do in their name. Because after all, the scientist in some ways is a luxury that society need not support.
So, the first thing is to explain supersymmetry. And Ive got a couple of stories that I use to do that for the general public. I often have occasion to give lectures on the topic and what have you. One of the things I tell them is well, gee, you know, if you look at our world, it looks like its composed of basically two major parts. One of those parts is stuff like us. Were made of, like, electrons, and protons, and neutrons. And all of these objects have a property which is kind of interesting, something that everybody knows, namely that you cant put your hand through a wall without busting it. Now that may seem like its not very physical, but ultimately that statement can be translated to something called the Exclusion Principle. Since were principally fermions, no two fermions can occupy the same space at the same time. And thats close enough for a general lay discussion of what the Exclusion Principle is.
On the other hand, if you take something like light, you find its very different, so lets go through some thought experiments. Lets take two flashlights, aim the two beams of the flashlights at each other and turn them on. What happens? Well, the two beams pass right through each other, nothing at all happens. Now take two water hoses and do the same thing. Now of course you see that the water starts splattering. And although that scattering is mostly electrical, even if you could turn off the electrical charges, then youd find that the Exclusion Principle would drive the scattering.
So our worlds composed of these two major pieces. And the thing thats really weird about our world is, like I said, stuff like us seems mostly to be fermions. The other half - energy, light, gravity, what we physicists like to call gauge fields, are all bosons. So why does our universe have this strange dichotomy, where stuff cannot pass through each other, but light and energy can? In fact, wouldnt the world be sort of more balanced, more symmetrical, or even supersymmetrical, if there were some forms of energy that would scatter each other just the way that stuff, matter, does, and if there were some forms of matter that could pass right through each other just the way energy does?
Well thats the basic idea of supersymmetry -- to say that matter can either be fermion or boson, and that energy can either be fermion or boson. So the idea of supersymmetry actually breaks an interesting stereotype. And let me argue by analogy here. All Republicans are supposed to be conservatives, and all Democrats are supposed to be liberals. At least thats the stereotype. But, in fact, some Democrats are conservative. And some Republicans, are, well, moderate.
So, you can break the stereotype also in the world of particles, and thats the idea of supersymmetry. Its purely hypothetical, but we sure hope its there, because it will be very interesting for the next millennium.

In order to learn supersymmetry and supergravity, one has to churn through a lot of excruciating calculations. Why should we believe this is a beautiful idea?
Because its first of all not a beautiful idea. I think the bottom line on the difficulty in learning something like supersymmetry or supergravity has to do with the following statement: I dont know if its possible to construct a starship, but Im pretty sure that the first person who figures out whether we can construct starships will probably be working on superstrings, supersymmetry, M-theory, something in that class of very difficult mathematical constructions. So the idea is not that its painless for us to get there, but the possible benefits for our species are so enormous that it is worth some of our time to make the investment to go through all these terrible things like worrying about minus signs and factors of twos and pis and all the things that graduate students will recognize in doing their homework.
For someone who carries out a life in research, in some sense that part of life never changes. Its like you always have a homework assignment thats due the next day, and you keep on churning and churning through it. So its the benefit, its not the actual pain. I guess its a bit like having babies. I hear thats painful, too. As the father of two children, I can tell you that the results of that are just marvelous.

What do you think are the prospects for observing direct evidence of supersymmetry in future high energy physics experiments?
Well, first of all, Im extremely hopeful. Im someone who spent their entire career, starting around 1970, and here we are in the year 2000, thinking about the possibility that our world has supersymmetry in it. Our best chance for observing direct evidence for supersymmetry will occur sometime after the year 2007. Hopefully at that point in time, the Large Hadron Collider in Geneva, Switzerland, will turn on, and we may have our first chance at forming these new forms of matter and energy, sometimes called superpartners, which are breaking the stereotypes that I described to you earlier.
Im hopeful, a number of us are hopeful, and if we are successful in discovering these forms of matter and energy, it will set an agenda for high technology for well into the next millennium. Its sort of like if we could go back in time to the 1870s, the 1860s, when people were first thinking about electricity. At that point there was a physicist named J.G. Stoney, who one day had a crazy idea and said, I could understand a certain result in the experiment, if there was this thing, which he later named the electron. We all know how that story worked out, because our beepers, our computers, all of our high technology depends on the fact that that crazy dream of Stoneys was in fact reality.
And thats where we will be once again. Well be setting up a signpost to the new high technology. So its very exciting for those of us whove been here for a very long time.

Jim Gates points to his book on supersymmetry.

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