Background
Polymath projects are a form of open Internet collaboration aimed towards a major mathematical goal, usually to settle a major mathematical problem. This is a concept introduced in 2009 by Tim Gowers and is in line with other forms of Internet mathematical research activity which include MathOverflow.
Former and current projects
The polymath wiki page gives a description and links to former polymath projects and much additional information. So far, there were about 10 polymath projects of which 6-7 led to intensive research, and among those 3-4 were successful. (There were several MathOverflow questions motivated by running polymath projects, especially questions related to polymath5.) Those projects ran over Gowers's blog (polymath1, polymath5 and others), Tao's blog (polymath8), the Polymath Blog (administered by Tao, Gowers, Nielsen, and me) (polymath4 and polymath7), and my blog (polymath3).
Updates (Before Nov 2016) There were a couple of additional polymath-type projects. (Nov '15, 2016) Currently, polymath10 on Erdős-Rado delta system conjecture is running on my blog.(New, Dec 29, '15) Terry Tao posted (on behalf of Dinesh Thakur) an interesting proposal for a polymath project regarding identities for irreducible polynomials Update: problem solved by David Speyer. ( January 31, 2016) Tim Gowers launched on his blog polymath11 on Frankl's union-closed conjecture.
Updates (Before January 2018) : Timothy Chow launched polymath12 on Rota's basis conjecture (February 24, 2017). (It was proposed as an answer to this question here.) (May 14, 2017) Tim Gowers is running a polymath-like project polymath13 on "Intransitive dices". (Dec 24 2017) A spontaneous polymath project, polymath14, over Tao's blog: A problem was posed by Apoorva Khare was presented and discussed and openly and collectively solved. (And the paper arxived.)
Update (January 25,2018) A new polymath project is emerging on Tao's blog: Polymath proposal: upper bounding the de Bruijn-Newman constant. Update: This is polymath15 which seems very active and quite successful. (wikipage)
Updates (April 14, 2018, June, 2019) Dustin Mixon and Aubrey de Grey have launched Polymath16 over at Dustin’s blog. The project is devoted to the chromatic number of the plane (Wikipage) following Aubrey de Grey's example showing that the chromatic number of the plane is at least 5. See also a proposal post and discussion thread over the polymath blog, and a proposal over here. Polymath 16 was now concluded.
Update, June 2019 Terry Tao initiated a sort of polymath attempt to solve the following problem conditioned on some conjectures from arithmetic algebraic geometry: Is there any polynomials $P$ of two variables with rational coefficients, such that the map $ P: \mathbb Q \times \mathbb Q \to \mathbb Q$ is a bijection? This is a famous 9-years old open question on MathOverflow.
Update, March 2020: On Terry Tao's blog, Polymath proposal: clearinghouse for crowdsourcing COVID-19 data and data cleaning requests. The proposal is to: (a) a collection of public data sets relating to the COVID-19 pandemic, (b) requests for such data sets, (c) requests for data cleaning of such sets, and (d) submissions of cleaned data sets. (Proposed by Chris Strohmeier after discussions among several mathematicians.)
Update (January 12, 2021) A polyTCS blog-based project was launched a year ago by Rupei Xu and Chloe Yang. It contains several interesting proposals.
Former proposals for future projects
There were also 10-20 additional serious proposals. A few proposals of various nature (from which polymath5 was selected) are gathered in this post on Gowers's blog, and several that appeared on various places are summarized on the polymath Wiki and also on the polymath blog. The polymath projects so far consisted of an attempt to solve a specific open problem but some of the proposals were of different nature.
More background
So far, polymath projects, while getting considerable attention and drawing enthusiasm, (and some controversy,) were limited in scope within mathematics and among mathematicians.
In most cases a small team of participants were the devoted contributed and in some cases those devoted participants were experts in the relevant area. Thus projects may apply primarily to experts in a specific field of mathematics. In all existing examples the project itself had some general appeal.
For a polymath project, in addition to the main task of trying to reach or at least greatly advance the goals of the specific project there are secondary goals of trying to understand the advantages and limitation of the polymath concept itself, and of trying to openly record the thought process of different participants towards the specific goal.
The question
The question is simple:
Make additional proposals for polymath projects.
Summary of proposals (updated: January 12, 2021)
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The LogRank conjecture. Proposed by Arul.
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The circulant Hadamard matrix conjecture. Proposed by Richard Stanley.
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Finding combinatorial models for the Kronecker coefficients. Proposed by Per Alexandersson.
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Eight lonely runners. Proposed by Mark Lewko.
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A problem by Ruzsa: Finding the slowest possible exponential growth rate of a mapping $f:N→Z$ that is not a polynomial and yet shares with (integer) polynomials the congruence-preserving property $n−m∣f(n)−f(m)$. Proposed by Vesselin Dimitrov.
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Finding the Matrix Multiplication Exponent ω. (Running time of best algorithm for matrix multiplication.) Proposed by Ryan O'Donnell.
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The Moser Worm problem and Bellman's Lost in a forest problem. Proposed by Philip Gibbs.
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Rational Simplex Conjecture ( by Cheeger and Simons). Proposed by Sasha Kolpakov.
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Proving that for every integer $m$ with $|m| \le c(\sqrt{n}/2)^n$ there is an $n \times n$ 0-1 matrix matrix whose determinant equals $m$.
Proposed by Gerhard Paseman. -
Proving or disproving that the Euler's constant is irrational.
Proposed by Sylvain JULIEN. -
The Greedy Superstring Conjecture. Proposed by Laszlo Kozma.
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Understanding the behavior and structure of covering arrays. Proposed by Ryan.
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The group isomorphism problem, proposed by Arul based on an early proposal by Lipton.
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Frankl's union closed set conjecture (Proposed by
Dominic van der Zypen; Also one of the proposals by Gowers in this post). (Launched) -
Komlos's conjecture in Discrepancy Theory. Proposed by Arul.
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Rota's Basis Conjecture. Proposed by Timothy Chow. Launched on the polymath blog.
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To show that $2^n+5$ composite for almost all positive integers $n$. (Might be too hard.) Proposed by me.
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To prove a remarkable combinatorial identity on certain Permanents. Proposed by me. Update, Aug 6, 2016: settled!
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Real world applications of large cardinals Proposed by Joseph van Name.
There were a few more proposals in comments. -
A project around a cluster of tiling problems. In particular: Is the Heech number bounded for polygonal monotiles? Is it decidable to determine if a single given polygonal tile can tile the plane monohedrally? Even for a single polyomino? Proposed by Joseph O'Rourke
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To prove that $\sum \frac{\sin (2^n)}{n}$ is a convergent series. Proposed by
JAck D'aurizio -
Major questions in the field of stereotype spaces and their applications, proposed by Sergei Akbarov.
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The Erdos-Straus conjecture, proposed by Amit Maurya
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The Collatz conjecture, proposed by Amit Maurya.
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Indecomposability of image transformations, proposed by Włodzimierz Holsztyński
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Is there a degree seven polynomial with integer coefficients such that (1) all of its roots are distinct integers, and (2) all of its derivative's roots are integers?, Proposed by Benjamin Dickman.
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The Cartan determinant conjecture for quiver algebras, proposed by Mare.
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The number of limit cycles of a polynomial vector field, Proposed by Ali Taghavi.
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Small unit-distance graphs with chromatic number 5, proposed by Noam Elkies. Became Polymath16, see above.
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(new) Lower bounds for average kissing numbers of non-overlapping spheres of different radii Proposed by Sasha Kolkapov.
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(new) A uniformly distributed random variable decomposition conjecture proposed by Sil.
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(new) The 3ᵈ conjecture and the flag-number conjecture proposed by me.
Proposed rules (shortened):
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All areas of mathematics including applied mathematics are welcome.
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Please do explain what the project is explicitly and in some details (not just link to a paper/wilipedea). Even if the project appeals to experts try to give a few sentences for a wide audience.
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Please offer projects that you genuinely think to be potentially suitable for a polymath project.
(Added) Criteria that were proposed for a polymath project.
Joel David Hamkins asked for some criteria that have been proposed for what kind of problem would make a good polymath project?
I don't think we have a clear picture on criteria for good polymath projects and there could be good projects of various kind. But the criteria for the first project are described by Gowers (I modified the wording to make them not specific in one sentence), and they seem like good criteria for a first project
in a new field be it algebraic geometry, algebraic topology, group theory, logic, or set theory (to mention a few popular MO tags).
" I wanted to choose a genuine research problem in my own area of mathematics, rather than something with a completely elementary statement or, say, a recreational problem, just to show that I mean this as a serious attempt to do real mathematics and not just an amusing way of looking at things I don’t really care about. This means that in order to have a reasonable chance of making a substantial contribution, you probably have to be a fairly experienced [researcher in the field of research]. So I’m not expecting a collaboration between thousands of people, but I can think of far more than three people who are suitably qualified.
Other criteria were that I didn’t want to choose a famous unsolved problem, or a problem where I had no idea whatever where to start. For a first attempt, it seemed a better idea to choose a problem that I’d love to solve, about which I already have some ideas, but in which I don’t (yet) have a significant emotional investment.
Does the problem split naturally into subtasks? That is, is it parallelizable? I’m actually not completely sure that that’s what I’m aiming for. … I’m interested in the question of whether it is possible for lots of people to solve one single problem rather than lots of people to solve one problem each.
However, my contention would be that any reasonably complex solution to a problem is somewhat parallelizable and becomes increasingly so as one thinks about it."
Best Answer
8 Lonely Runners
[The aim of this proposal would be to find a project that a massive number of people (including amateur mathematicians) might actually effectively contribute to, which is a somewhat different goal than the other proposed polymath projects.]
A longstanding problem in diophantine approximation is the lonely runner conjecture which states:
This has been proven for $n \leq 7$ runners by Barajas and Serra but is open for higher values of $n$. It is known that one can reduce to the case where all of the speeds are integers. From here each of the previously considered cases (for $n \leq 7$) can be treated by case analysis based on various congruence conditions of of the $n$ integer speeds.
Extrapolating from the work on $n \leq 7$, the work of splitting into and proving the various cases should be highly parallelizable and many cases completely elementary. At the same time, however, one might well imagine that more creative/sophisticated/clever arguments could be developed or applied to particular cases, which could have the potential of even yielding progress the general case as well.
In fact, recently Terry Tao proved that one needs only consider a finite number of cases for each $n$ (unfortunately the number of such sets is extremely large even for $n=8$ and beyond the capabilities of computer search) so in some sense this proof strategy is guaranteed to work with enough effort.