## Saturday, February 24, 2018

### Julian Schwinger: 100 years

Harvard's climate skeptic Willie Soon has sent me a link to the Crimson article describing a Harvard event that took place last week. Julian Schwinger was born on February 12th, 1918. 100 years and 2 days later, some of his grateful junior collaborators didn't forget and gathered.

It's useful to know that 1918+100=2018 which is why we face the celebrations of 100 years of Schwinger, Feynman, and Czechoslovakia in this year (the third co-winner of that QED Nobel prize was Tomonaga *1906, not Czechoslovakia).

There are dozens of TRF blog posts that mention Schwinger, including a short biography and a review of renormalization where I picked him as a symbol.

Schwinger was a brilliant member of the generation (a group) that was born one generation (a unit of time) after the founders of quantum mechanics (those were born around 1900-1902) – well, we assume that the parents were marginally enabled teenagers. ;-)

This simple comparison adequately reflects the progress that was taking place. The folks born around 1900 had to discover the foundations of quantum mechanics. But the generation born around 1918 was already taking it for granted – quantum mechanics was served instead of breast milk to the likes of Schwinger and Feynman and there were no "interpreting" crackpots yet which is why these boys could enjoy the milk, indeed – and they could apply it in non-trivial new contexts.

I think that I have dedicated much less time to Schwinger than what he would deserve, especially given my rather intense interactions with his students over the years. Schwinger taught at Harvard and in the high-energy group, we were using schwinger.harvard.edu for the primary e-mail – at least, in my case, up to the moment when I got a new Linux workstation, feynman.harvard.edu, into my office.

This tomb is located at the historical Mt Auburn cemetery in Cambridge, Massachusetts. Too bad I don't remember it and maybe I've never seen it – despite the fact that I have spent a nontrivial amount of time in the peaceful environment of Mt Auburn, see e.g. this random video. My roommate for several years was constantly "birding" there.

The tomb reveals that his wife was a few months older than he was and, more importantly, it says $$\alpha / 2\pi$$. That's, of course, the leading (one-loop) correction to the anomalous magnetic moment; $$\alpha\approx 1/137.036$$ is the fine-structure constant. I think that the introduction of loops to physics was less revolutionary than the birth of quantum mechanics but from some intellectual viewpoint, it may be fair to say that it required a very similar amount of intelligence or creativity.

Famously, renormalization was too dirty for Paul Dirac – which was his opinion backed by similar sentiments as the anti-quantum views held by some early quantum mechanics skeptics. But Schwinger was persuaded by the partial evidence that despite the ultraviolet divergences, you should take the loops seriously and they hide some high-precision information about all the tiny corrections that quantum mechanics implied for quantum mechanics.

At the high school, I studied some introduction to quantum field theory based on Schwinger's approach – one that was based on Schwinger's "source theory" developed around 1966. The word "theory" looks strange because it seems to be just a pedagogical approach to quantum field theory i.e. to the "same theory". But it's plausible that Schwinger believed otherwise – and he thought that the sources etc. were needed or very helpful to understand the strong nuclear interaction. If he did indeed believe it, I think it was unreasonable because the difference between "source theory" and the more conventional presentations of quantum field theory is rather clearly just a difference in the formalism, not in the beef, so whatever can be formulated in one language may be translated to the other languages.

Like Schwinger himself, four of his students have received a Nobel prize, including Mottelson (with Bohr's son), Sheldon Glashow (in 1979), Roy Glauber (in 2005), and Walter Kohn (for chemistry). Indirectly, biochemist Wally Gilbert has also had Schwinger as his supervisor but I forgot the details.

It's funny how tightly one may get integrated to this community by having spent some years at Harvard as a physicist. I've never met Ben Mottelson (he's still alive) – despite the fact that his name sounds as if I were his father (who had some... fun in Scandinavia). But otherwise... We've interacted with Sheldon Glashow often, during dinners etc., and I've been using his office for a few years. Roy Glauber was still at Harvard and we celebrated his 2005 Nobel prize. Walter Kohn is the guy after whom the KITP hall in Santa Barbara is named – I've spent over half a year there although I don't remember having talked to Kohn.

And Wally Gilbert was the boss of our Harvard Society of Fellows, so we have chatted with him during numerous Monday dinners and we have even been to his house. Among other things, this founder of Biogen has an impressive arts collection where vases and little sculptures often cost millions of dollars. We would make jokes over there, touch a sculpture or a vase with a friend's arm, and say: "Now you will have a small spasm in your muscles and you'll be lighter by X million dollars."

The article in the Crimson discusses Schwinger's lectures. He began to talk immediately when he entered the classroom. His speech was rather quiet but very comprehensible and students generally took this stuff as a drug. No one has ever dared to ask a question.

I must laugh when I read these testimonies about that "perfect teacher" and compare them e.g. with the "perfect teachers" according to the ideology of Hejný's method that we debated at a conference last week. According to Hejný's method, the teacher mustn't ever try to convey any prepared information to the student's brain, let alone try to correct the student's mistakes, because that would be a form of rape. So the teacher must sit as if she were invisible and the kids must enjoy the time and do whatever they want and discover all the scientific discoveries by themselves.

That doesn't sound like Schwinger's classroom, does it? ;-)

If I don't count this blog post, the article in The Crimson is the only news article that I see that remembers the 100th anniversary of Julian Schwinger's birth – and there are no comments underneath that article. This fact looks rather disappointing to me, especially if you appreciate how many important people whose lives and careers were affected by Schwinger are still alive.

Things would be different if men like Glashow and Gilbert were occasionally fighting for the honor to be allowed to post a TRF blog post. :-)