Chen-Ning Yang

楊振寧 · 1922–2025 · why our technique carries his name

The coloured notes are from Tony's AI assistant, whose job is to keep people straight where he has missed something — a fact, a caveat, or an observation of its own. We have left them a different colour rather than blending them in.

When we take a program written decades ago and build a proved replacement, we do one more thing. We run the old one and the new one on the same inputs and watch where they part.

Where they disagree is where the interesting things are. That is the Yang Technique.

The teaching

I have it second-hand that he told students in China that if they ever got the tiniest glimpse of something, they should investigate it. I cannot show you where he said it.

correction, and it is ours — this page first printed that as a documented quotation and placed it at the CP violation. Both were wrong. We could not source the words in his lectures, interviews or the published record, so it now stands as what it is: something heard, repeated honestly, and unverified. And the physics was ours to get right — Yang and Lee did parity violation in 1956; CP violation was Cronin and Fitch in 1964, a different discovery eight years later. Corrected rather than quietly removed, because a site that tells you to check its claims should show you the one it got wrong.

That is the whole discipline and it is harder than it sounds. First time we ran this, 403 of 407 cases agreed. Ninety-nine percent. Everything in me said round it off.

The four were a silent overflow in the original. A field too small for a result nobody had checked, quietly truncating, for decades.

observation — the difficulty is not that the teaching is subtle. Ninety-nine percent is a number you can report; four unexplained cases is more work for you. Our harness prints no percentage, so there is nothing to round.

So we chase the four. Every one has to be explained: our fault, their fault, or the comparison is broken. You have to say which.

And there is more in it than method. A small thing has everyone against it. The books, the people around you, and the ninety-nine percent that agrees. To go after four cases out of four hundred and seven you have to back yourself, and be willing to be the one who wasted a week on nothing.

That is what happened to both of them. Everybody knew parity held. They asked anyway. Her colleagues told her the experiment wasn't worth the trouble. She did it anyway.

Part of what he was telling those students is believe in yourself.

observation — which sits awkwardly beside the rest of this site, and should. Do not trust, check is the rule here. But you have to believe you saw something before you would bother measuring it, so the nerve comes first and the check comes second.

What he did

With Tsung-Dao Lee, in 1956, he asked whether parity holds in the weak interaction — the question Chien-Shiung Wu then answered. They took the 1957 Nobel for it, the first Chinese-born winners in physics.

Two years before that, with Robert Mills, he wrote down the gauge theory that carries both their names. Yang–Mills describes three of the four forces and the standard model rests on it. It is probably the bigger thing. It won him nothing at the time.

Nurture is genius

He could have spent the rest of his life being eminent. He went back and taught instead.

Tsinghua, where he had grown up on the campus as a boy. Honorary director of its Center for Advanced Study in 1997, professor in 1999. He gave up his American citizenship in 2015 and took Chinese citizenship back. And he taught the first-year course himself.

observation — he was in his late seventies, with a Nobel and the gauge theory the standard model is built from. First-year physics is the class a department gives to whoever cannot refuse it. He asked for it.

That is what I mean by nurture is genius. Not teaching as the nice thing a great man does afterwards. The building of other people was the work.

He died in Beijing on 18 October 2025, aged 103.

Chien-Shiung Wu →