This morning Sir Michael Atiyah gave a presentation at the Heidelberg Laureate Forum with a claimed proof of the Riemann hypothesis. The Riemann hypothesis (RH) is the most famous open problem in mathematics, and yet Atiyah claims to have a simple proof.

Simple proofs of famous conjectures

If anyone else claimed a simple proof of RH they’d immediately be dismissed as a crank. In fact, many people have sent me simple proofs of RH just in the last few days in response to my blog post, and I imagine they’re all cranks [1]. But Atiyah is not a crank. He won the Fields Medal in 1966 and the Abel prize in 2004. In other words, he was in the top echelon of mathematicians 50 years ago and has kept going from there. There has been speculation that although Atiyah is not a crank, he has gotten less careful with age. (He’s 89 years old.)

QuinteScience, source of the image above, quoted Atiyah as saying

Solve the Riemann hypothesis and you’ll become famous. But if you’re already famous, you run the risk of becoming infamous.

If Atiyah had a simple self-contained proof of RH that would be too much to believe. Famous conjectures that have been open for 150 years don’t have simple self-contained proofs. It’s logically possible, but practically speaking it’s safe to assume that the space of possible simple proofs has been very thoroughly explored by now.

But Atiyah’s claimed proof is not self-contained. It’s really a corollary, though I haven’t seen anyone else calling it that. He is claiming that a proof of RH follows easily from his work on the Todd function, which hasn’t been published. If his proof is correct, the hard work is elsewhere.

Andrew Wiles’ proof of Fermat’s last theorem was also a corollary. He proved a special case of the Taniyama–Shimura conjecture, and at end of a series of lectures noted, almost as an afterthought, that his work implied a proof to Fermat’s last theorem. Experts realized this was where he was going before he said it. Atiyah has chosen the opposite approach, presenting his corollary first.

Connections with physics

Atiyah has spoken about connections between mathematics and physics for years. Maybe he was alluding to his work on the fine structure constant which he claims yields RH as a corollary. And he is not the only person talking about connections between the Riemann hypothesis specifically and physics. For example, there was a paper in Physical Review Letters last year by Bender, Brody, and Müller stating a possible connection. I don’t know whether this is related to Atiyah’s work.

Fine structure constant

The fine structure constant is a dimensionless physical constant α, given by

where e is the elementary charge, ε 0 is vacuum permittivity, ħ is the reduced Planck constant, and c is the speed of light in a vacuum. Its value is roughly 1/137.

The Todd function

The Todd function T is a function introduced by Atiyah, named after his teacher J. A. Todd. We don’t know much about this function, except that it is key to Atiyah’s proof. Atiyah says the details are to be found in his manuscript The Fine Structure Constant which has been submitted to the Proceedings of the Royal Society.

Atiyah says that his manuscript shows that on the critical line of the Riemann zeta function, the line with real part 1/2, the Todd function has a limit ж and that the fine structure constant α is exactly 1/ж. That is,

lim y → ∞ T(1/2 + yi) = ж = 1/α.

Now I don’t know what he means by proving that a physical constant has an exact mathematical value; the fine structure constant is something that is empirically measured. Perhaps he means that in some mathematical model of physics, the fine structure constant has a precise mathematical value, and that value is the limit of his Todd function.

Or maybe it’s something like Koide’s coincidence where a mathematical constant is within the error tolerance of a physical constant, an interesting but not necessarily important observation.

Taking risks

Michael Atiyah is taking a big risk. I’ve seen lots of criticism of Atiyah online. As far as I know, none of the critics have a Fields Medal or Abel Prize in their closet.

Atiyah’s proof is probably wrong, just because proofs of big theorems are usually wrong. Andrew Wiles’ proof of Fermat’s Last Theorem had a flaw that took a year to patch. We don’t know who Atiyah has shown his work to. If he hasn’t shown it to anyone, then it is almost certainly flawed: nobody does flawless work alone. Maybe his proof has a patchable flaw. Maybe it is flawed beyond repair, but contains interesting ideas worth pursuing further.

The worst case scenario is that Atiyah’s work on the fine structure constant and the Todd function is full of holes. He has made other big claims in the last few years that didn’t work out. Some say he should quit doing mathematics because he has made big mistakes.

I’ve made big mistakes too, and I’m not quitting. I make mistakes doing far less ambitious work than trying to prove the Riemann hypothesis. I doubt I’ll ever produce anything as deep as a plausible but flawed proof of the Riemann hypothesis.

Update

The longer paper has been leaked, presumably without permission from Atiyah or the Royal Society, and it doesn’t seem to hold up. No one is saying the proof can be patched, but there has been some discussion about whether the Todd trick could be useful.

In writing this post I wanted to encourage people to give Atiyah a chance, to wait until more was known before assuming the proof wasn’t good. I respect Atiyah as a mathematician and as a person—I read some of his work in college and I’ve had the privilege of meeting him on a couple occasions—and I hoped that he had a proof even though I was skeptical. I think no less of him for attempting a to prove a big theorem. I hope that I’m swinging for the fences in my ninth decade.

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[1] I don’t call someone a crank just because they’re wrong. My idea of a crank is someone without experience in an area, who thinks he has found a simple solution to a famous problem, and who believes there is a conspiracy to suppress his work. Cranks are not just wrong, they can’t conceive that they might be wrong.