SCOTT SIMON, HOST:

 

There are lots of lists as the year draws to a close: best films, best books, Persons of the Year. This year, NPR is looking at the numbers that tell this year's story. So, our math guy, Keith Devlin, has a nomination for number of the year. He joins us now from Stanford University, where he's a professor of something that's too long for me to state. Keith, thanks very much for being with us.

 

KEITH DEVLIN: Hi, Scott. Good to be with you again.

 

SIMON: All right. Drum roll, please: the number of the year is...

 

DEVLIN: The number of the year is 2.

 

SIMON: All right. Now, I was hoping for 0, as it represents the number of World Series won by the Cubs since the Roman era. But why 2?

 

DEVLIN: Because the big story in mathematics this last year - and it was a big story and an exciting story - was to do with something called the twin prime conjecture, which is about two primes and how close two primes can be. Primes, remember, are these whole numbers bigger than 1 that cannot be divided evenly by any other number. So, a 3, 5, 7. The closest two primes can be together is 2. 5 and 7 is a pair of twins, 11 and 13 is; 17 and 19 is. But as you go up the numbers, the primes themselves get thin - they thin out. It's like going up in a space rocket and the air gets thinner. And so it wasn't at all clear whether you could get infinitely many of these twin primes. In fact, we still don't know that we can, but, boy, have we come pretty close to being able to prove it.

 

SIMON: Have they created new numbers? I mean, what kind of mystery can there be about this when, as far as I'm concerned, I thought all the numbers had already been assigned.

 

DEVLIN: Ah. But it's like gossiping about your friends. It's not the fact that you have the friends, it's things you learn about them that you didn't know and you think, wow, have they been doing this all that time?

 

SIMON: I'm surprised you have any friends after that, but go ahead.

 

DEVLIN: I'm losing them as I speak, I realize that. What was really exciting about this was until, I think it was maybe April or May of this year, nobody had been able to prove that there were infinitely many of these pairs. And the question's been around for - in a sense, it's been around for thousands of years. It's been looked at in detail for 100 years. No one really came close to proving it. But then in May, this adjunct faculty member at the University of New Hampshire got pretty close by mathematical standards.

 

SIMON: This is Yitang Zhang, right?

 

DEVLIN: That's right. He actually proved that if you relax friendship to being not adjacent but to being within 70 million of each other then in fact there are infinitely many pairs of primes. Now, that doesn't sound a great deal but going down from no knowledge to 70 million was a big step for mathematicians. And it started an avalanche because mathematicians have been in a world record hunt, like Phelps does when he gets in a swimming pool. And in the space of a few months, it went down from 70 million to 600. Now, we still got a way to go from 600 to 2, which is the twin prime conjecture...

 

SIMON: This was James Maynard at the University of Montreal.

 

DEVLIN: Yeah, James Maynard, he got the current world record, which is 600. And that was very recently. That was November the 19th he announced it. It was all done on the Internet, and at one stage the record was tumbling at about every half-hour. So, mathematics, which usually takes place over months and years, for a period of a few months was going gangbusters fast. And this record was tumbling down. It seems to have settled at 600. It might creep down. I don't think the methods that we've got now will bring us down to 2. But 2 is within grasp. And because this ancient problem about 2 is within grasp, I would say 2 is absolutely the number of the year in mathematics. It's the number mathematicians have been talking about.

 

SIMON: Keith, are there implications for this finding for those of us who think it's got nothing to do with us whatsoever should know nevertheless?

 

DEVLIN: You can bet that whenever there's an advance to do with prime numbers, the intelligence community is absolutely on top of it. Because in our knowledge of the prime numbers lies pretty well all of the secret codes that we use for communications around the world. It's all to do with the difficulty of computing some of the things we know theoretically happen in mathematics.

 

SIMON: Keith Devlin, our math guy and distinguished professor at Stanford. Thanks very much for being with us.

 

DEVLIN: Nice to be with you, Scott.

 

SIMON: And, by the way, we'd like to know the number you'd use to describe 2013. You can join us on Twitter, Tumblr, Instagram or Facebook. The hashtag is NPRNoty. It's almost like NPR naughty, isn't it? But not quite.