#104 - Leonard Susskind

**Craig Cannon** (0:00)
Hey, how's it going? This is Craig Cannon, and you're listening to Y Combinator's podcast.
Today's episode is with Leonard Susskind. Leonard's a professor of theoretical physics at Stanford University, and he's regarded as one of the fathers of string theory. He's written several books, and if you're just getting into physics, I'd recommend checking out his Theoretical Minimum series. He also has over 100 lectures on YouTube, and I'll link those up in the show notes. All right, here we go.
What I wanted to start with is, you've often been characterized as someone with non-traditional, kind of out-there ideas, some of which have become part of the physics canon, some of which, who knows what happened.

**Leonard Susskind** (0:40)
Who of you all became part of the physics canon?
Every single one of them. I've never made a mistake.

**Craig Cannon** (0:45)
Of course, all right, well, thanks for coming on the podcast. You're the first person who's never made a mistake.
I was curious, who do you think is your most outlandish friend?

**Leonard Susskind** (0:56)
Wait, come back to your previous question for a moment. I am very mainstream. I am not at all an alternative thinker. This is some misconception, which I don't know how it happened, but my physics has been extremely mainstream. It may have been that at the beginning of some of the ideas, people were not quite ready, but they very quickly caught on. It's just not true that I was some kind of alternative, what should we call it?
I don't know what the right word is.

**Craig Cannon** (1:35)
Yeah, some kind of radical thinker.

**Leonard Susskind** (1:36)
Not at all. Not at all. Now, I spent a lot of time thinking about, what should we call them, conflicts of principle, situations where things were not fitting together properly, and thought a lot about them, and eventually came to the conclusion that you had to change things, or that you had to break the mold a little bit.
And I think that's probably where this reputation came from. But these were things that really, there were no alternatives to.
What was it that Sherlock Holmes said? Do you remember the quote? When you've tried all possibilities, and I forget the exact, but roughly speaking, when you've tried everything and it doesn't work, whatever remains must be the truth, no matter how outlandish or something like that.

**Craig Cannon** (2:31)
So a little bit like Occam's razor.

**Leonard Susskind** (2:32)
Yeah, well, a little bit like Occam's razor. But in particular, when you've tried everything and it doesn't work, there may still be something left that you haven't, that you haven't tried yet because you thought it was too outlandish. Well, you got to try it.
And I think that probably is the source of some of this mythology about me as a radical. But I am the most conservative physicist imaginable.

**Craig Cannon** (3:00)
Okay, so what's an example, then, of a friend who is more outlandish, more radical than you?

**Leonard Susskind** (3:05)
Oh, Freeman Dyson.
I can't exactly call him a friend, but I know him a little bit. He is what you might call a contrarian. He enjoys running against the grain, and he sometimes says some brilliant and smart things. Like all contrarians, he's got a very large probability of being wrong.

**Craig Cannon** (3:32)
And he's willing to.

**Leonard Susskind** (3:33)
My friend Herade Tuft, I don't know if you know his name, he's a very famous physicist. He's also a bit of a contrarian.
He's far more out there than I've ever been.
Was Dick Feynman a contrarian? No, he was about as mainstream as you can be. But also had his own, he had his own very special scientific personality. And I suspect that's also true of me, that my way of thinking, my way of doing things is probably different than most people. And so, yeah, it did lead to this contrarian, this view of me as a contrarian, as a radical, but it was absolutely wrong.

**Craig Cannon** (4:19)
And do you see physics kind of birthing more contrarians in the modern paradigm where experiments are so expensive to kind of execute at this point? Or do they have to be kind of more mainstream to get things done?

**Leonard Susskind** (4:35)
Well, unfortunately, I think you have to be really mainstream. Sometimes I think too much. Sometimes I think too much. By mainstream now, I mean people are often trained within a framework which is fairly tight and rigid.
And I sometimes think maybe a little more free thinking out there might be useful. Free thinking, but that doesn't mean being a contrarian. A contrarian is somebody who is contrary just for the sake of being contrary.