2014-12-94

FeatureFor me, personally, it felt like being able to sneak into thegarage and watch a high-performance engine being built upfrom scratch: something I could never do but could appreciatethe end result and admire the process.8 Andrew SutherlandAndrew Sutherland is a principal research scientist at MIT.I first heard about Zhang’s result shortly after he spokeat Harvard in May 2013. The techniques he used were welloutside my main area of expertise and I initially followeddevelopments purely as a casual observer. It was only afterreading Scott Morrison’s blog, where people had begun discussingimprovements to Zhang’s bound, that I realised therewas an interesting and essentially self-contained sub-problem(finding narrow admissible tuples) that looked amenable tonumber-theoretic combinatorial optimisation algorithms, asubject with which I have some experience. I ran a few computations,and once I saw the results it was impossible to resistthe urge to post them and join the Polymath8 project. Asidefrom interest in the prime gaps problem, I was curious aboutthe Polymath phenomenon and this seemed like a great opportunityto learn about it.Like others, I was surprised by how much time I endedup devoting to the project. The initially furious pace of improvementsand the public nature of the project made a veryaddictive combination and I wound up spending most of thatsummer working on it. This meant delaying other work butmy collaborators on other projects were very supportive. Icertainly do not begrudge the time I devoted to the Polymath8effort; it was a unique opportunity and I’m glad I participated.In terms of the Polymath experience, there are a couple ofthings that stand out in my mind. In order to make the kindof rapid progress that can be achieved in a large scale collaboration,the participants really have to be comfortable withmaking mistakes in a forum that is both public and permanent.This can be a difficult adjustment and there was certainlymore than one occasion when I really wished I could retractsomething I had written that was obviously wrong. But oneeventually gets used to working this way; the fact that everybodyelse is in the same boat helps. Actually, I think beingforced to become more comfortable with making mistakescan be a very positive thing. This is how we learn.The other thing that impressed me about the project is thewide range of people that made meaningful contributions. Notonly were there plenty of participants who, like me, are notexperts in analytic number theory, there were at least a fewfor whom mathematics is not their primary field of research.I think this is major strength of the Polymath approach: it facilitatescollaboration that would otherwise be very unlikelyto occur.It is perhaps worth highlighting some of the features ofthis project that made it a particularly good Polymath candidate.First, the problem we were working on was well-knownand naturally attracted a lot of interested observers; this madeit easy to recruit participants. Second, we had a clearly definedgoal (improving the bound on prime gaps) and a metricagainst which incremental progress could be easily measured;this kept the project moving forward with a lot of momentum.Third, the problem we were working on naturally splitinto sub-problems that were more or less independent; thisallowed us to apply a lot of brain power in parallel and whenone branch of the project would slow down, another mightspeed up. Finally, we had an extremely capable project leader,one who could see the whole picture and was very adept at organisingand motivating people.I don’t mean to suggest that these attributes are all necessaryingredients for a successful Polymath project but I thinkit is fair to say that, at least in this case, they were sufficient.9 Wouter CastryckWouter Castryck is a postdoctoral fellow of FWO-Vlaanderen.In June last year, one of my colleagues informed me aboutthe Polymath8 project and, in particular, about the programmingchallenge of finding admissible k-tuples whose diameterH is as small as possible. I decided to give it a try and join“team H” of the production line. Luckily, I jumped in shortlyafter the project had started, at a point where there was stillsome low-hanging fruit. Like others, I experienced how addictiveit was to search for smaller values of H, while tryingnew computational tricks and combining them with ideas ofthe other participants. Because the value of k kept decreasingas well, new challenges popped up every other day or so,which fuelled the excitement. The whole event was intenseand highly interactive and progress was made at an incrediblespeed. (It is not academic to say so but when the otherteams managed to decrease k to a size where our computationalmethods became superfluous, this was a bit of a disappointment.Luckily, Maynard’s work on prime triples, quadruples,etc., put larger values of k back into play.)Along the way, it became clear that the online arena inwhich it all took place attracted many spectators and it feltlike a privilege to be in there. It did require a mental switch topost naive (and sometimes wrong) ideas on the public forumbut in the end I agree with Andrew Sutherland that this is notnecessarily a bad thing.Gradually, by reading the blog posts, I also learned aboutthe other parts of Zhang’s proof. On a personal level, thisI found the most enriching thing: participating in the Polymath8project was a very stimulating way of learning and appreciatinga new part of mathematics. This is definitely thanksto the clarifying and enthusing way in which Terence Tao administeredthe project. At the same time, I must admit thatI did not grasp every detail from A to Z. From the point ofview of a “coauthor”, this is somewhat uncomfortable but itmay be inherent to the production line model along which thePolymath projects are organised.10 Emmanuel KowalskiEmmanuel Kowalski is a professor at ETH.I remember reading the first blog posts of T. Gowers concerningthe Polymath idea and briefly following the first stepsat that time. I was intrigued but did not participate. As faras I remember, my only public comment was a brief note afterthat progress was successful, which still illustrates how Ifeel about the way this idea turned out: it provides a striking,largely publicly available, illustration of the way mathematicalresearch works (or at least, often works...). Although20 EMS Newsletter December 2014