Exposé sur ABC

Sylvain

Bonjour,

Demain à Jussieu Go Yamashita doit faire un exposé de 60 minutes intitulé "a proof of the abc conjecture after Mochizuki". Si des intervenants du forum y assistent, ce serait sympa de nous faire part de vos impressions.

Bonne fin de week-end.

Héhéhé

A mon avis cela risque d'être un désastre. Ce n'est plus un secret pour personne qu'il y a une erreur non réparable dans les travaux de Mochizuki : le fameux corollaire 3.12.

Un papier est en préparation pour expliquer exactement où est l'erreur.

Sinon dans cet article de blog, de nombreux mathématiciens de premier plan expriment leurs doutes, notamment Peter Scholze (la nouvelle star de la géométrie algébrique qui a de grande chance d'être médaillé Fields 2018 cet été) et Terence Tao dont je me permets de recopier ici les mots :

Peter Scholze a écrit:

One small thing I would like to add is that most accounts indicate that no experts have been able to point to a place where the proof would fail. This is in fact not the case; since shortly after the papers were out I am pointing out that I am entirely unable to follow the logic after Figure 3.8 in the proof of Corollary 3.12 of Inter-universal Teichmüller theory part III: “If one interprets the above discussion in terms of the notation introduced in the statement of Corollary 3.12, one concludes [the main inequality].” Note that this proof is in fact the *only* proof in parts II and III that is longer than a few lines which essentially say “This follows from the definitions”. Those proofs, by the way, are completely sound, very little seems to happen in those two papers (to me). Since then, I have kept asking other experts about this step, and so far did not get any helpful explanation. In fact, over the years more people came to the same conclusion; from everybody outside the immediate vicinity of Mochizuki, I heard that they did not understand that step either. The ones who do claim to understand the proof are unwilling to acknowledge that more must be said there; in particular, no more details are given in any survey, including Yamashita’s, or any lectures given on the subject (as far as they are publicly documented). [I did hear that in fact all of parts II and III should be regarded as an explanation of this step, and so if I am unable to follow it, I should read this more carefully… For this reason I did wait for several years for someone to give a better (or any) explanation before speaking out publicly.]

Terence Tao a écrit:

Thanks for this. I do not have the expertise to have an informed first-hand opinion on Mochizuki’s work, but on comparing this story with the work of Perelman and Yitang Zhang you mentioned that I am much more familiar with, one striking difference to me has been the presence of short “proof of concept” statements in the latter but not in the former, by which I mean ways in which the methods in the papers in question can be used relatively quickly to obtain new non-trivial results of interest (or even a new proof of an existing non-trivial result) in an existing field. In the case of Perelman’s work, already by the fifth page of the first paper Perelman had a novel interpretation of Ricci flow as a gradient flow which looked very promising, and by the seventh page he had used this interpretation to establish a “no breathers” theorem for the Ricci flow that, while being far short of what was needed to finish off the Poincare conjecture, was already a new and interesting result, and I think was one of the reasons why experts in the field were immediately convinced that there was lots of good stuff in these papers. Yitang Zhang’s 54 page paper spends more time on material that is standard to the experts (in particular following the tradition common in analytic number theory to put all the routine lemmas needed later in the paper in a rather lengthy but straightforward early section), but about six pages after all the lemmas are presented, Yitang has made a non-trivial observation, which is that bounded gaps between primes would follow if one could make any improvement to the Bombieri-Vinogradov theorem for smooth moduli. (This particular observation was also previously made independently by Motohashi and Pintz, though not quite in a form that was amenable to Yitang’s arguments in the remaining 30 pages of the paper.) This is not the deepest part of Yitang’s paper, but it definitely reduces the problem to a more tractable-looking one, in contrast to the countless papers attacking some major problem such as the Riemann hypothesis in which one keeps on transforming the problem to one that becomes more and more difficult looking, until a miracle (i.e. error) occurs to dramatically simplify the problem.

From what I have read and heard, I gather that currently, the shortest “proof of concept” of a non-trivial result in an existing (i.e. non-IUTT) field in Mochizuki’s work is the 300+ page argument needed to establish the abc conjecture. It seems to me that having a shorter proof of concept (e.g. <100 pages) would help dispel scepticism about the argument. It seems bizarre to me that there would be an entire self-contained theory whose only external application is to prove the abc conjecture after 300+ pages of set up, with no smaller fragment of this setup having any non-trivial external consequence whatsoever.

Sylvain

Alors, y avait-il des membres du forum dans l'assistance ?