Of course, one might say, there are certain kinds of problems that lend themselves to huge collaborations. One has only to think of the proof of the classification of finite simple groups, or of a rather different kind of example such as a search for a new largest prime carried out during the downtime of thousands of PCs around the world. But my question is a different one. What about the solving of a problem that does not naturally split up into a vast number of subtasks? Are such problems best tackled by 
It seems to me that, at least in theory, a different model could work: different, that is, from the usual model of people working in isolation or collaborating with one or two others. Suppose one had a forum (in the non-technical sense, but quite possibly in the technical sense as well) for the online discussion of a particular problem. The idea would be that anybody who had anything whatsoever to say about the problem could chip in. And the ethos of the forum — in whatever form it took — would be that comments would mostly be kept short. In other words, what you would not tend to do, at least if you wanted to keep within the spirit of things, is spend a month thinking hard about the problem and then come back and write ten pages about it. Rather, you would contribute ideas even if they were undeveloped and/or likely to be wrong.
This suggestion raises several questions immediately. First of all, what would be the advantage of proceeding in this way? My answer is that I don’t know for sure that there would be an advantage. However, I can see the following potential advantages.
(i) Sometimes luck is needed to have the idea that solves a problem. If lots of people think about a problem, then just on probabilistic grounds there is more chance that one of them will have that bit of luck.
(ii) Furthermore, we don’t have to confine ourselves to a purely probabilistic argument: different people know different things, so the knowledge that a large group can bring to bear on a problem is significantly greater than the knowledge that one or two individuals will have. This is not just knowledge of different areas of mathematics, but also the rather harder to describe knowledge of particular little tricks that work well for certain types of subproblem, or the kind of expertise that might enable someone to say, “That idea that you thought was a bit speculative is rather similar to a technique used to solve such-and-such a problem, so it might well have a chance of working,” or “The lemma you suggested trying to prove is known to be false,” and so on—the type of thing that one can take weeks or months to discover if one is working on one’s own.
(iii) Different people have different characteristics when it comes to research. Some like to throw out ideas, others to criticize them, others to work out details, others to re-explain ideas in a different language, others to formulate different but related problems, others to step back from a big muddle of ideas and fashion some more coherent picture out of them, and so on. A hugely collaborative project would make it possible for people to specialize. For example, if you are interested in the problem and like having slightly wild ideas but are less keen on the detailed work of testing those ideas, then you can just suggest the ideas and hope that others will find them interesting enough to test or otherwise respond to.
In short, if a large group of mathematicians could connect their brains efficiently, they could perhaps solve problems very efficiently as well.
The next obvious question is this. Why would anyone agree to share their ideas? Surely we work on problems in order to be able to publish solutions and get credit for them. And what if the big collaboration resulted in a very good idea? Isn’t there a danger that somebody would manage to use the idea to solve the problem and rush to (individual) publication?
Here is where the beauty of blogs, wikis, forums etc. comes in: they are completely public, as is their entire history. To see what effect this might have, imagine that a problem was being solved via comments on a blog post. Suppose that the blog was pretty active and that the post was getting several interesting comments. And suppose that you had an idea that you thought might be a good one. Instead of the usual reaction of being afraid to share it in case someone else beat you to the solution, you would be afraid not to share it in case someone beat you to that particular idea. And if the problem eventually got solved, and published under some pseudonym like Polymath, say, with a footnote linking to the blog and explaining how the problem had been solved, then anybody could go to the blog and look at all the comments. And there they would find your idea and would know precisely what you had contributed. There might be arguments about which ideas had proved to be most important to the solution, but at least all the evidence would be there for everybody to look at.
True, it might be quite hard to say on your CV, “I had an idea that proved essential to Polymath’s solution of the *** problem,” but if you made significant contributions to several collaborative projects of this kind, then you might well start to earn a reputation amongst people who read mathematical blogs, and that is likely to count for something. (Even if it doesn’t count for all that much now, it is likely to become increasingly important.) And it might not be as hard as all that to put it on your CV: you could think of yourself as a joint author, with the added advantage that people could find out exactly what you had contributed.
And what about the person who tries to cut and run when the project is 85% finished? Well, it might happen, but everyone would know that they had done it. The referee of the paper would, one hopes, say, “Erm, should you not credit Polymath for your crucial Lemma 13?” And that would be rather an embarrassing thing to have to do.
Now I don’t believe that this approach to problem solving is likely to be good for everything. For example, it seems highly unlikely that one could persuade lots of people to share good ideas about the Riemann hypothesis. At the other end of the scale, it seems unlikely that anybody would bother to contribute to the solution of a very minor and specialized problem. Nevertheless, I think there is a middle ground that might well be worth exploring, so as an experiment I am going to suggest a problem and see what happens.
I think it is important to do more than just say what the problem is. In order to try to get something started, I shall describe a very preliminary idea I once had for solving a problem that interests me (and several other people) greatly, but that isn’t the holy grail of my area. Like many mathematical ideas, mine runs up against a brick wall fairly quickly. However, like many brick walls, this one doesn’t quite prove that the approach is completely hopeless—just that it definitely needs a new idea.
It may be that somebody will almost instantly be able to persuade me that the idea is completely hopeless. But that would be great—I could stop thinking about it. And if that happens I’ll dig out another idea for a different problem and try that instead.
It’s probably best to keep this post separate from the actual mathematics, so that comments about collaborative problem-solving in general don’t get mixed up with mathematical thoughts about the particular problem I have in mind. So I’ll describe the project in my next post. Actually, make that my next post but one. The next post will say what the problem is and give enough background information about it to make it possible for anybody with a modest knowledge of combinatorics (or more than a modest knowledge) to think about it and understand my preliminary idea. The following post will explain what that preliminary idea is, and where it runs into difficulties. Then it will be over to you, or rather over to us. I’ve already written the background-information post, but will hold it back for a few days in case the responses to this post affect how I decide to do things.
The blog medium is almost certainly not optimal for this purpose, so if a serious discussion starts with lots of worthwhile contributions, then I’ll look into the possibility of migrating it over to some purpose-built site. If anyone has any suggestions for this (apart from the obvious one of using the Tricki — I’m not sure that’s appropriate just yet though) then I’d be delighted to receive them. My feelings at the moment are that blogs are too linear—it would be quite hard to see which comments relate to which, which ones are most worth reading, and so on. A wiki, on the other hand, seems not to be linear enough—it would be quite hard to see what order the comments come in. So my guess is that the ideal forum would probably be a forum: if someone knows an easy way to set up a mathematical forum, I might even do that. But if the discussion is on this blog, then I might from time to time try to assess where it has got to and create new posts if I feel that genuine progress has been made that can be summarized and then built on.
I’ve been thinking of doing this for a long time. The reason I’ve suddenly decided to go ahead is that I followed a couple of links from this post on Michael Nielsen’s blog, and discovered that, unsurprisingly, others have had similar ideas, and some people are already doing research in public. But the idea still seems pretty new, particularly when applied to one single mathematics problem, so I wanted to try it out when it was still fresh. (I would distinguish what I am proposing from what goes on at the n-category café, which is an excellent example of collaborative mathematics, but focused on an entire research programme rather than just one problem.)
To finish, here is a set of ground rules that I hope it will be possible to abide by. At this stage I’m just guessing what will work, so these rules are subject to change. If you can see obvious flaws let me know.
1. The aim will be to produce a proof in a top-down manner. Thus, at least to start with, comments should be short and not too technical: they would be more like feasibility studies of various ideas.
2. Comments should be as easy to understand as is humanly possible. For a truly collaborative project it is not enough to have a good idea: you have to express it in such a way that others can build on it.
3. When you do research, you are more likely to succeed if you try out lots of stupid ideas. Similarly, stupid comments are welcome here. (In the sense in which I am using “stupid”, it means something completely different from “unintelligent”. It just means not fully thought through.)
4. If you can see why somebody else’s comment is stupid, point it out in a polite way. And if someone points out that your comment is stupid, do not take offence: better to have had five stupid ideas than no ideas at all. And if somebody wrongly points out that your idea is stupid, it is even more important not to take offence: just explain gently why their dismissal of your idea is itself stupid.
5. Don’t actually use the word “stupid”, except perhaps of yourself.
6. The ideal outcome would be a solution of the problem with no single individual having to think all that hard. The hard thought would be done by a sort of super-mathematician whose brain is distributed amongst bits of the brains of lots of interlinked people. So try to resist the temptation to go away and think about something and come back with carefully polished thoughts: just give quick reactions to what you read and hope that the conversation will develop in good directions.
7. If you are convinced that you could answer a question, but it would just need a couple of weeks to go away and try a few things out, then still resist the temptation to do that. Instead, explain briefly, but as precisely as you can, why you think it is feasible to answer the question and see if the collective approach gets to the answer more quickly. (The hope is that every big idea can be broken down into a sequence of small ideas. The job of any individual collaborator is to have these small ideas until the big idea becomes obvious — and therefore just a small addition to what has gone before.) Only go off on your own if there is a general consensus that that is what you should do.
8. Similarly, suppose that somebody has an imprecise idea and you think that you can write out a fully precise version. This could be extremely valuable to the project, but don’t rush ahead and do it. First, announce in a comment what you think you can do. If the responses to your comment suggest that others would welcome a fully detailed proof of some substatement, then write a further comment with a fully motivated explanation of what it is you can prove, and give a link to a pdf file that contains the proof.
9. Actual technical work, as described in 8, will mainly be of use if it can be treated as a module. That is, one would ideally like the result to be a short statement that others can use without understanding its proof.
10. Keep the discussion focused. For instance, if the project concerns a particular approach to a particular problem (as it will do at first), and it causes you to think of a completely different approach to that problem, or of a possible way of solving a different problem, then by all means mention this, but don’t disappear down a different track.
11. However, if the different track seems to be particularly fruitful, then it would perhaps be OK to suggest it, and if there is widespread agreement that it would in fact be a good idea to abandon the original project (possibly temporarily) and pursue a new one — a kind of decision that individual mathematicians make all the time — then that is permissible.
12. Suppose the experiment actually results in something publishable. Even if only a very small number of people contribute the lion’s share of the ideas, the paper will still be submitted under a collective pseudonym with a link to the entire online discussion.
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