Steven Strogatz knows that for some people, the subject of math brings back dreaded grade school memories of challenging word problems and formulas. As Professor of Applied Mathematics at Cornell University, Strogatz strives to apply mathematics to the curiosities of everyday life. He's explained head-scratching phenomena as a frequent guest on WNYC's *Radiolab*, like why a Slinky seems to defy the laws of gravity. And in his "The Elements of Math" series for *The New York Times*' Opinionator blog, he applied group theory to explain the optimal system to flip a mattress. The series sparked the creation of his latest book, *The Joy of X: A Guided Tour of Math, From One to Infinity*.

When Strogatz sat down with host Ophira Eisenberg at The World Science Festival, he challenged the assumption that in a world of computers and calculators, we don't need to know math. "But then the question to me is like, 'Why do I need to watch Michael Jordan play basketball?'" Strogatz said. "Or, 'Why do I need to listen to music?' You don't really need to, but your life will be richer and happier if you do."

In an Ask Me Another Challenge, we found a way to quiz Strogatz on social networks, based on the "Six Degrees of Kevin Bacon" game. Math enthusiasts have their own version of the game featuring prolific mathematician Paul Erdős, who published more than 1,500 research papers. Strogatz had to identify people who have Erdős-Bacon numbers – that is, people who can be linked to Bacon through acting roles as well as to Erdős through academic paper authorship. (Fun fact: Strogatz has an Erdős-Bacon number of 4, thanks to his appearance in a documentary about social networks that featured – who else? — Kevin Bacon.)

In the video below, Strogatz tells a story on WNYC's *Radiolab* about how an experiment with pendulums in grade school taught him the meaning of the Law of Nature.

*This segment originally ran on July 30, 2013.*

Transcript

OPHIRA EISENBERG, HOST:

Welcome back to ASK ME ANOTHER, NPR and WYNC's hour of trivia, puzzles, and word games. I'm Ophira Eisenberg and joining me is author and math whiz, to say the least, Cornell professor extraordinaire Steven Strogatz.

(APPLAUSE)

EISENBERG: Welcome to ASK ME ANOTHER.

STEVE STROGATZ: Thank you very much. I'm thrilled to be here.

EISENBERG: When did you know you liked math? As a child were you a math kid?

STROGATZ: Hmm. I did always like math but I had a pivotal moment when there was a teacher who mentioned a certain question that he'd been asking for years and he said he'd never seen any student answer this question. And then he went on to say - I mean, I sat up straight at that point.

EISENBERG: And how old are you?

STROGATZ: Maybe 13 or 14.

EISENBERG: OK.

STROGATZ: And then he said actually he didn't know how to do the problem.

EISENBERG: Really?

STROGATZ: Never heard any teacher say something like that before. You want the problem, don't you?

EISENBERG: I want the problem. I want to know just even the context of the problem.

STROGATZ: The problem was a problem about triangles and it goes like this. If two angle bisectors of a triangle have the same length the triangle has to be Isosceles. Prove it. I thought what's so hard about this? I mean, it sounded like other geometry problems and so I tried thinking about it and couldn't do it. So I started thinking about it every day, including in French class.

You know, like, when they're conjugating the verb train is going around the room and it's coming towards me I'm still thinking about angle bisectors. Same thing with playing basketball. People would pass it to me, bounce off my knee, because I'm off in triangle world. So I spent maybe six months thinking about this continuously and finally came up with something I thought was a proof. It was a Sunday morning and I asked him could I come to your house and show it to you?

(LAUGHTER)

EISENBERG: Wow. And he was like no.

STROGATZ: No.

(LAUGHTER)

STROGATZ: Well, yeah, he should've. But he was a good teacher.

EISENBERG: Yeah.

STROGATZ: I showed up. He was there in his pajamas with his little kids. I showed him this proof. He checked it line by line. He said it's a proof.

EISENBERG: Wow.

(APPLAUSE)

STROGATZ: Thank you.

EISENBERG: So at that point did you think...

STROGATZ: So then I was hooked.

EISENBERG: Yeah. You were like I'm done.

STROGATZ: Because I started making up questions for myself that I didn't know the answer to just for the fun of getting back into that euphoric feeling of being puzzled and wanting to solve it.

EISENBERG: And you decided to put together this wonderful book, "Joy of X." We were talking about real life math.

STROGATZ: That refers to "Joy of Cooking."

EISENBERG: "Joy of Cooking"? Oh, yes.

(LAUGHTER)

EISENBERG: I see the wordplay.

STROGATZ: Yeah, yeah, yeah.

EISENBERG: So why do you think math gets such a bad rap? I had one good teacher in high school that helped me but in general, you know, I just always thought I was not very good at math.

STROGATZ: Hmm. You thought you weren't good at math.

EISENBERG: Yes.

STROGATZ: And some people feel they're just not good at it or they'll say I don't have a math head. Or they'll say I was good until - and then they tell you I got to geometry or I was good until I got to word problems in algebra or something. For a lot of people, they hit the wall and then they're discouraged. Other people will tell me I was good at it the whole time, I just never saw the point of it. You know?

EISENBERG: Right. And what do you say to those people? What is the point to having it in their life?

STROGATZ: Well, there's all kinds of points. For me, when people ask - of course the question is why do I need to learn math? And it's not really that you need to learn it. Yes, you do, if you're going to be an engineer or a computer scientist. You will actually need it. But if you're not in that kind of profession you don't really need it. But then to me the question is like why do I need to watch Michael Jordan play basketball?

Or why do I need to listen to music? You don't really need to, but your life will be richer and happier if you do.

(APPLAUSE)

EISENBERG: That makes me care.

(LAUGHTER)

EISENBERG: It does make me care. You are one of the founders of the theories of social networks.

STROGATZ: Well, let me give credit to the real founder. It's a student. Duncan Watts...

EISENBERG: OK.

STROGATZ: ...was my grad student.

EISENBERG: Oh, OK.

STROGATZ: He was interested in sort of where physics and math meet social sciences and so we got to talking. I had given him a problem that I was interested in about how things get in synch and we were specifically interested in how crickets can chirp in unison. Now you might say who cares about crickets? That's a fair question.

(LAUGHTER)

STROGATZ: But think about it this way. In your heart you have special cells that keep your heart beating properly and those cells, those pacemaker cells, have to be in synch. And it's a lot easier to measure crickets getting in synch than your pacemaker cells. But they might be using the same kind of math and same principles.

EISENBERG: Right.

STROGATZ: So anyway, we were busy studying the crickets and one time he had a conversation with his dad who said, just offhandedly, do you realize you're only six handshakes from the president of the United States or from anybody else on Earth? This idea of six degrees of separation, which people were talking about at the time in the middle '90s. And he asked me how would everything about synchronization would change if the crickets were connected like that? If they were listening in this six degrees way.

And that was a brand new question. No one knew anything about that.

EISENBERG: It's like that game people play in college.

STROGATZ: Yes.

EISENBERG: The six degrees...

STROGATZ: The Kevin Bacon game.

EISENBERG: The Kevin Bacon game.

STROGATZ: Yeah. But it turned out that provided really interesting data that allowed us to test some of our theories. Because the Internet movie "Database" which has all the actors in the history of movies going back to silent movies, it gave us a way to test a lot of what we were thinking about with a real social network, if you like, the Hollywood network.

EISENBERG: So is - question one, are we really all separated by six degrees?

STROGATZ: Yeah, it really is true. It is true. You know, considering it's seven billion people on Earth you might think the number would be hundreds or thousands or millions. It's not. It's close to - it's around five or six.

EISENBERG: Wow. And do you know how many degrees you are separated from Kevin Bacon?

(LAUGHTER)

STROGATZ: That, I do - well, yeah. But that's easy. Because I was in a documentary about him.

EISENBERG: Oh.

STROGATZ: About the math of Kevin Bacon.

(APPLAUSE)

STROGATZ: So that's not a good - that's not a good - I mean, you could do someone else.

EISENBERG: So the answer is one?

STROGATZ: Yeah. It's kind of one.

EISENBERG: Well, that's amazing.

STROGATZ: Yeah. Thank you.

(LAUGHTER)

EISENBERG: Well, that's a little sneak peek as to what we would like you to solve for us...

STROGATZ: OK.

EISENBERG: ...coming up. So I first need to ask you, are you ready to solve a different kind of problem? Prove a little something different on the ASK ME ANOTHER stage?

STROGATZ: Hmm. Yes. I am ready.

EISENBERG: You are ready? Fantastic.

STROGATZ: All right.

EISENBERG: How about a hand for our VIP, Steven Strogatz?

(APPLAUSE)

EISENBERG: With this round let me bring back our one man house band, Jonathan Coulton.

(APPLAUSE)

JONATHAN COULTON: Hello.

EISENBERG: And of course our puzzle guru, John Chaneski.

(APPLAUSE)

JOHN CHANESKI: OK.

EISENBERG: So Steven, we just talked about your Kevin Bacon number, that you are one degree from separation from Kevin Bacon. And it turns out that math scholars have their own version of this game through a prolific mathematician named Paul Erdos. In his lifetime, Erdos published more than 1,500 research papers with over 500 different co-authors who all have an Erdish number of one.

Of course, it was only a matter of time before someone came up with the Erdish Bacon number which is the sum of one's Erdish and Bacon numbers. Naturally. So, Steven, this quiz is about some of the other people who have Erdish Bacon numbers. Some are actors, some are academics, all are amazing.

(LAUGHTER)

EISENBERG: We're going to ask you to identify them based on our clues and if you get enough right, Anna Byers of Louisville, Kentucky, will get a special ASK ME ANOTHER prize. Stakes are high. Are you ready?

STROGATZ: OK.

EISENBERG: This actress has a Bacon number of two, having starred in "Closer" with Julia Roberts who starred in "Flatliners" with Kevin Bacon in 2002. As a Harvard undergraduate, she co-authored a paper studying the frontal lobes of infants, giving her an Erdish number of four.

STROGATZ: Who is Natalie Portman?

(APPLAUSE)

EISENBERG: That is correct.

CHANESKI: It is my job to remind contestants they are not on "Jeopardy!" by the way.

(LAUGHTER)

COULTON: This British actor got his co-author byline after suggesting a study to determine whether the brain structures of political conservatives were physically different from those of liberals. It turns out they are. Now we need a study on the brains of women who've seen him play Mr. Darcy in "Pride and Prejudice."

STROGATZ: Hmm.

EISENBERG: Oh.

STROGATZ: Hmm.

EISENBERG: Mm-hmm.

STROGATZ: I can picture him.

EISENBERG: Steven, yes.

COULTON: He's beautiful, isn't he?

(LAUGHTER)

STROGATZ: Is he the stuttering king?

COULTON: Yes.

EISENBERG: Yes.

STROGATZ: In...

COULTON: Yes, he is.

STROGATZ: I'm having a little left hemisphere problem.

COULTON: Let's see. He shares his first name of a former Secretary of State.

STROGATZ: Oh.

EISENBERG: Wow, that's good.

COULTON: Whose last name was Powell.

STROGATZ: Oh, good. Thank you. Thank you. That would be Colin Firth.

EISENBERG: Yes.

(APPLAUSE)

STROGATZ: Thank you. So I think in math we would call that partial credit.

EISENBERG: On ASK ME ANOTHER we call that - you don't get anything.

COULTON: We call that wrong.

EISENBERG: Yeah.

STROGATZ: OK.

(LAUGHTER)

EISENBERG: As an undergraduate at UCLA, actress Danica McKellar co-authored a paper titled "Percolation and Gibbs States Multiplicity for Ferromagnetic Ashkin - Teller Models in Z2." I wrote the Z3 one. I don't know what she's talking about.

(LAUGHTER)

EISENBERG: She later wrote the book "Math Doesn't Suck" but you probably know her as Winnie Cooper on what early 1990s dramedy?

STROGATZ: "The Wonder Years."

EISENBERG: Yes.

(APPLAUSE)

EISENBERG: Can you quickly just describe to me your take on the percolation in Gibbs state multiplicity for ferromagnetic Ashkin Teller Models in the Z2?

STROGATZ: Classic.

EISENBERG: Yeah.

(LAUGHTER)

EISENBERG: Yeah. I hear what you're saying.

COULTON: It really does bring me back, you know?

(LAUGHTER)

COULTON: Because it was so different then. This baseball player is often included in Erdish-Bacon conversations because he and Erdish autographed a baseball together after receiving honorary degrees from Emory University on the same day. That's not the same thing as writing a paper with him, but if you count co-signing a baseball, his Erdish-Bacon number would be three.

STROGATZ: Hmm.

COULTON: The number you might best know him for is 755, the number of homeruns this Hall of Fame outfielder hit in his major league career.

STROGATZ: Hank Aaron.

CHANESKI: Yeah.

EISENBERG: Mm-hmm. Yeah.

(APPLAUSE)

EISENBERG: What do you think, John Chaneski?

CHANESKI: I think that's why we call him the Great Strogatzby. Because he answered so many questions right that Anna Byers receives a prize. Congratulations.

(APPLAUSE)

EISENBERG: Steven, you were everything I hoped for to the nth degree.

STROGATZ: Aw, thank you.

EISENBERG: How about a round of applause for our VIP Steven Strogatz?

(APPLAUSE)

(SOUNDBITE OF SONG, "PI")

COULTON: This is a song called "Pi." (singing) When ink and pen in hands of men inscribe your form bipedal P they draw an altar on which God has slaughtered all stability. No eyes could ever soak in all the places you anoint and yet to see you all a once we only need the point. Flirting with infinity, a geometric progeny that fit inside you, oh, so tight. Triangles that feel so right. 3.14159265358979323846264338329750288419716939937510582097494459.

(APPLAUSE)

EISENBERG: Jonathan Coulton. Transcript provided by NPR, Copyright NPR.