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Shimura-Taniyama-Weil (STW) Solved
timbo_red writes "The BBC report that an international team of scientists have solved the STW conjecture. I vaguely remember what this is from reading the Fermat book, I'll have to check it again. " This really has me interested in the conjecture. Anyone have any good links for background reading?
I read this a couple of days ago, and understood several of the words involved. Further reading, with decent enough explanations, can be found here.
Like the article says, Wiles solved a special case of STW to knock off Fermat's Last Theorem. I guess this is a proof of the general version (but the article is a little vague--any number theorists around who are in the loop?)
The existence of a proof of the full Taniyama-Shimura conjecture was announced at a conference by Kenneth Ribet on June, 21 1999 (Knapp 1999), and reported on National Public Radio's Weekend Edition on July 31, 1999. The proof was completed by Christophe Breuil, Brian Conrad, Fred Diamond, and Richard Taylor, building on the earlier work of Wiles and Taylor.
/. posts what we submit. Though, I think monitoring NPR would be a good source for stories -- they reported this one a while back. Perhaps links like this one to the real-audio recordings of their broadcasts might be a nice touch.
Before everybody starts screaming "this is old news" remember,
The Future of Human Evolution: Autonomy
Alright, I'm no expert on this stuff, but I'm going to take a stab at explaining why anyone would care about the STW conjecture.
First, let's start somewhere seemingly unrelated that may be easier to deal with: Physics; specifically, gravity. I'm working under the assumption that everyone knows what gravity is, so, good. There are other forces that do similar things in Physics, however. The most common are the "Strong" and "Weak" electromagnetic forces. The force that holds electrons close to an atom, and that bonds atoms to each other in molecules are examples of these forces.
Now in Physics, there is a holy grail of theory called the 'Grand Unification Theory'. This is big important stuff. In an amazing oversimplification, it suggests that there is a single formula that relates all of these forces together. We _expect_ this from intuition, we currently just don't have any idea how to prove it, although progress is being made all over the place.
Now, skip back to mathematics. Mathematics is split into tons of different areas. Statistics, Number Theory (the stuff normally used in cryptography), Calculus, and so on. Robert Langlands proposed that there is a Grand Unification Theory (GUT) of sorts for mathematics. This is commonly referred to as the Langlands Proposition (or Program, according to the BBC article).
Some years ago, Yukata Taniyama (The 'T' in STW) asserted a conjecture that did two things. First, if proved, it would bring elliptic curves and modular forms together in the spirit of the GUT, thus giving the Langlands program a big push. Secondly and, while not really more important, at least more interesting to the public, he showed that if his conjecture was proved, the most famous unproved theorem at the time would follow. I speak, of course, of Fermat's last theorem (FLT). This was the holy grail of math at the time.
A few years ago, Andrew Wiles proved enough of Taniyama's conjecture to prove FLT. This was what made STW mainstream; had this not happened, noone would care and the BBC story would probably be overlooked. But it did happen, made lots of papers, was flawed, fixed, flawed again, and currently is believed to be correct.
What recently happened, in the BBC story, is that the _rest_ of the STW conjecture was proved. Not just the part that Wiles used to show FLT, but all of it. In math this elevates STW from a conjecture to a theorem and makes mathematicians everywhere giddy with joy since the Langlands Program is slightly closer to being proved.
And of course, giddy mathematicians are the types who post stuff to Slashdot, which is why this article is here at all.
Was that any better?
I followed a one-semester graduate course (by Laurent Clozel) on the proof of the semistable case of the Shimura-Taniyama conjecture (the case proven originaly by Wiles and which concludes the proof of Fermat's theorem). So I can make a few comments on the subject.
The Shimura-Taniyama conjecture (Weil's name is attached to it for rather dubious reasons: essentially, he mentioned the conjecture — as an exercice for the interested reader! — in a book he published; Serge Lang is always ready to flame anyone calling the conjecture by Weil's name, so let us omit Weil) concerns a correspondance between certain modular forms and certain elliptic curves (actually with Galois representations in between the two). That is, it states that every elliptic curve is associated to a certain modular form (the association can be stated in many different ways: they have the same L function; the eigenvalues of the modular form for the Hecke operators can be deduced from the number of points of the elliptic curve on finite fields, and so on). This conjecture was known (i.e. formulated) long before any relation with Fermat's theorem was observed.
Gerhart Frey had noticed that if a counterexample (A,B,C) (with A+B+C=0, A, B and C being p-th powers) to Fermat's theorem were found it would yield an elliptic curve y=x(x-A)(x+B) having certain miraculous properties, including being ``semistable'' and possibly violating the Shimura-Taniyama conjecture. Using works of Jean-Pierre Serre, Ken Ribet was able to prove this remark of Frey, so that the Shimura-Taniyama conjecture, and in fact even only the Shimura-Taniyama conjecture for semistable elliptic curves, would imply Fermat's theorem.
At that point it became obvious that it would be only a matter of time before Fermat's theorem were proven. Andrew Wiles, was able to complete the task. His first proof contained a flaw (in trying to construct an Euler system), which was noticed by Luc Illusie, but with the help of Richard Taylor, Wiles was able to replace the technique of Euler systems and use Gorenstein rings instead (and some very fine points of commutative algebra) and correct the proof. The full proof (Wiles' ``Modular Elliptic Curves and Fermat's Last Theorem'' and Wiles and Taylor's ``Ring Theoretic Properties of Certain Hecke Algebras'') was published in Inventiones Mathematicæ. Thus, the case of Fermat's theorem was settled.
The general case of the ST conjecture was still unproven. However, soon after Wiles' result, Fred Diamond improvement over it. To understand it, you must know that semistability of an elliptic curve is a ``local'' property, i.e. it can be tested for each prime number. An E.C. is (globally) semistable iff it is semistable at every prime number. (It is always semistable at all but a finite number of primes.) Wiles' result required the E.C. to be semistable at all primes; Diamond refined that and proved the modularity of elliptic curves that are modular at 3 and 5. This was a considerable progress, and it was then pretty obvious that these last conditions would be eliminated. Now they have been (every elliptic curve is known to be modular), but this is more a question of technique than a fundamental improvement.
One might be tempted to think that the proof of the ST conjecture is fascinating. In fact, I found it (or at least the semistable case, which has, it would seem, the gist of the ideas) terribly boring. It is all a matter of controling the behavior of the ramified parts of the cohomology groups of some Galois representations, and it is done in a succession of lemmata, each one seeming exactly the same as the previous one. In fact, the experts' opinion is that the proof of the conjecture is technically difficult but fundamentally trivial in that it does not use any deep results from (algebraic) geometry.
The ST conjecture is part of a more general scheme called the ``Langlands programme''. The Langlands programme is a correspondance (which has not been formulated in a completely satisfactory way, as far as I know, let alone proven) between higher dimensional abelian varieties (elliptic curves are abelian varieties of dimension 1), Galois representations and modular forms (disclaimer: I don't know half of what I'm talking about here). ``Class field theory'', the climax of the number theory of the beginning of the century, is the case ``GL1'' of the Langlands programme (the abelian case). The Shimura-Taniyama conjecture was the case ``GL2'' of the same programme. Some other cases have been proven, such as ``Sp4'' (these funny acronyms refer to certain algebraic groups: GL is the General Linear group, and Sp is the Symplectic group).
The Langlands programme actually splits in two parts: the ``number field'' (or ``global'') Langlands programme, the hard number-theoretic part, of which the ST conjecture is a particular case, and the ``function field'' (or ``local'') Langlands programme, which is an easier analogue of more geometric content.
The major news recently is that the ``function field'' Langlands programme has been proven, by Laurent Lafforgue. This is much more important than the full proof of the ST conjecture. And it also means that Lafforgue will be getting the Fields medal in three years (mark my words).