- Some of the fascinating work you've done is in the space of supersymmetry, symmetry in general. Can you describe first of all what is supersymmetry? - Ah yes, so you remember the two buckets I told you about, perhaps earlier, so there are two buckets in our universe. So now I want you to think about drawing a pie that has four quadrants, so I want you to cut the piece of pie in fourths.

So in one quadrant I'm gonna put all the buckets that we talked about that are like the electron and the quarks, in a different quadrant I am going to put all the force carriers. The other two quadrants are empty. Now if you, I showed you a picture of that, you'd see a circle, there would be a bunch of stuff in one upper quadrant and stuff in others, and then I would ask you a question.

Does that look symmetrical to you? - No. - No, and that's exactly right because we humans actually have a very deeply programmed sense of symmetry. It's something that is part of that mystery of the universe. So how would you make it symmetrical? One way you could is by saying those two empty quadrants had things in them also, and if you do that, that's supersymmetry.

So that's what I understood when I was a graduate student here at MIT in 1975, when the mathematics of this was first being born. Supersymmetry was actually born in the Ukraine in the late '60s, but we had this thing called the Iron Curtain, so we Westerners didn't know about it.

But by the early '70s, independently, there were scientists in the West who had rediscovered supersymmetry, Bruno Zemino and Julius Vest were their names. So this was around '71 or '72 when this happened. I started graduate school in '73, so around '74, '75, I was trying to figure out how to write a thesis so that I could become a physicist the rest of my life.

I had a great advisor, Professor James Young, who had taught me a number of things about electrons and weak forces and those sorts of things. But I decided that if I was going to have a really, an opportunity to maximize my chances of being successful, I should strike it out in a direction that other people were not studying.

And so as a consequence, I surveyed ideas that were being developed, and I came across the idea of supersymmetry. And it was so, the mathematics was so remarkable that I just, it bowled me over. I actually have two undergraduate degrees. My first undergraduate degree is actually mathematics, and my second is physics, even though I always wanted to be a physicist.

Plan A, which involved getting good grades, was mathematics. I was a mathematics major thinking about graduate school, but my heart was in physics. - If we could take a small digression, what's to you the most beautiful idea in mathematics that you've encountered in this interplay between math and physics?

- It's the idea of symmetry. The fact that our innate sense of symmetry winds up aligning with just incredible mathematics, to me, is the most beautiful thing. It's very strange but true that if symmetries were perfect, we would not exist. And so even though we have these very powerful ideas about balance in the universe in some sense, it's only when you break those balances that you get creatures like humans and objects like planets and stars.

So although they are a scaffold for reality, they cannot be the entirety of reality. So I'm kind of naturally attracted to parts of physics and attracted to parts of science and technology where symmetry plays a dominant role. - And not just, I guess, symmetry as you said, but the magic happens when you break the symmetry.

- The magic happens when you break the symmetry. - Okay, so diving right back in, you mentioned four quadrants. - Yes. - Two are filled with stuff, two buckets. And then there's crazy mathematical thing, ideas for filling the other two. What are those things? - So earlier, the way I described these two buckets is I gave you a story that started out by putting us in a dusty room with two flashlights.

And I said, "Turn on your flashlight, I'll turn on mine. "The beams will go through each other." And the beams are composed of force carriers called photons. They carry the electromagnetic force. And they pass right through each other. So imagine looking at the mathematics of such an object, which you don't have to imagine people like me do that.

So you take that mathematics, and then you ask yourself a question. You see, mathematics is a palette. It's just like a musical composer is able to construct variations on a theme. Well, a piece of mathematics in the hand of a physicist is something that we can construct variations on.

So even though the mathematics that Maxwell gave us about light, we know how to construct variations on that. And one of the variations you can construct is to say, suppose you have a force carrier for electromagnetism that behaves like an electron in that it would bounce off of another one.

That's changing a mathematical term in an equation. So if you did that, you would have a force carrier. So you would say, first, it belongs in this force-carrying bucket. But it's got this property of bouncing off like electrons. So you say, well, gee, wait, no, that's not the right bucket.

So you're forced to actually put it in one of these empty quadrants. So those sorts of things, basically, we give them, so the photon mathematically can be accompanied by a photino. It's the thing that carries a force but has the rule of bouncing off. In a similar manner, you could start with an electron.

And you say, okay, so write down the mathematics of an electron. I know how to do that. A physicist named Dirac first told us how to do that back in the late '20s, early '30s. So take that mathematics, and then you say, let me look at that mathematics and find out what in the mathematics causes two electrons to bounce off of each other, even if I turn off the electrical charge.

So I could do that. And now let me change that mathematical term. So now I have something that carries electrical charge, but if you take two of them, I'm sorry, if you turn their charges off, they'll pass through each other. So that puts things in the other quadrant. And those things we tend to call, we put the S in front of their name.

So in the lower quadrant here, we have electrons. In this now newly filled quadrant, we have electrons. In the quadrant over here, we had quarks. Over here, we have squarks. So now we've got this balanced pi, and that's basically what I understood as a graduate student in 1975 about this idea of supersymmetry, that it was going to fill up these two quadrants of the pi in a way that no one had ever thought about before.

So I was amazed that no one else at MIT found this an interesting idea. So it led to my becoming the first person in MIT to really study supersymmetry. This is 1975, '76, '77. And in '77, I wrote the first PhD thesis in the physics department on this idea because I was drawn to the balance.

- Drawn to the symmetry. So what does that, first of all, is this fundamentally a mathematical idea? So how much experimental, and we'll have this theme, it's a really interesting one. When you explore the world of the small, and in your new book talking about Approving Einstein, right, that we'll also talk about, there's this theme of kind of starting it, exploring crazy ideas first in the mathematics, and then seeking for ways to experimentally validate them.

Where do you put supersymmetry in that? - It's closer than string theory. It has not yet been validated. In some sense, you mentioned Einstein, so let's go there for a moment. In our book, Proving Einstein Right, we actually do talk about the fact that Albert Einstein in 1915 wrote a set of equations which were very different from Newton's equations in describing gravity.

These equations made some predictions that were different from Newton's predictions. It actually made three different predictions. One of them was not actually a prediction, but a postdiction because it was known that Mercury was not orbiting the sun in the way that Newton would have told you. And so Einstein's theory actually describes Mercury orbiting in the way that it was observed as opposed to what Newton would have told you.

So that was one prediction. The second prediction that came out of the theory of general relativity, which Einstein wrote in 1915, was that if you, so let me describe an experiment and come back to it. Suppose I had a glass of water, and I filled the glass up, and then I moved the glass slowly back and forth between our two faces.

It would appear to me like your face was moving, even though you weren't moving. I mean, it's actually, and what's causing it is because the light gets bent through the glass as it passes from your face to my eye. So Einstein, in his 1915 theory of general relativity, found out that gravity has the same effect on light as that glass of water.

It would cause beams of light to bend. Now, Newton also knew this, but Einstein's prediction was that light would bend twice as much. And so here's a mathematical idea. Now, how do you actually prove it? Well, you've got to watch, yes. - Just a quick pause on that, just the language you're using.

He found out. - I can say he did a calculation. - It's a really interesting notion that one of the most, one of the beautiful things about this universe is you can do a calculation and combine with some of that magical intuition that physicists have, actually predict what would be, what's possible to experiment to validate.

- That's correct. - So he found out in the sense that there seems to be something here and mathematically it should bend, gravity should bend light this amount. And so therefore that's something that could be potentially, and then come up with an experiment that could be validated. - Right.

And that's the way that actually modern physics, deeply fundamental modern physics, this is how it works. Earlier we spoke about the Higgs boson. So why did we go looking for it? The answer is that back in the late 60s, early 70s, some people wrote some equations and the equations predicted this.

So then we went looking for it. (silence) (silence) (silence) (silence) (silence) (silence) (silence)