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
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 Schrodingers 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 Id 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 doesnt 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 thats what I want
to do, because I know how to make up stuff real well, so if Im 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
didnt 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 parts 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 whats 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 hadnt
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, Ill help you if I can when you get stuck trying
to learn the material, but youre 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 worlds 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 dont think you actually sell an idea like supersymmetry
to the general public. The first thing I think thats truly important
is to try to get the public to understand what it is that were proposing.
Im 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 Ive 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 its composed of basically two major parts. One of those
parts is stuff like us. Were 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 cant
put your hand through a wall without busting it. Now that may seem like
its not very physical, but ultimately that statement can be translated
to something called the Exclusion Principle. Since were principally
fermions, no two fermions can occupy the same space at the same time.
And thats close enough for a general lay discussion of what the Exclusion
On the other hand, if you take something like light, you find its very
different, so lets go through some thought experiments. Lets 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 youd find that the Exclusion
Principle would drive the scattering.
So our worlds composed of these two major pieces. And the thing thats
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, wouldnt 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 thats 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
thats 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
thats the idea of supersymmetry. Its purely hypothetical, but we sure
hope its 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 its 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 dont know if its possible
to construct a starship, but Im 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 its
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 twos and pis 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. Its like you always have a homework assignment
thats due the next day, and you keep on churning and churning through
it. So its the benefit, its not the actual pain. I guess its a bit
like having babies. I hear thats 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
Well, first of all, Im extremely hopeful. Im 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.
Im 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. Its sort of
like if we could go back in time to the 1870s, the 1860s, 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 Stoneys was in fact reality.
And thats where we will be once again. Well be setting up a signpost
to the new high technology. So its very exciting for those of us whove
been here for a very long time.