How crazy is theoretical physics? Sidney Coleman was one of my favorite people in rheoretical physics. His office door was always open to me. And he was one of the only people who ever seemed to be “natively quantum”. And he was hysterically funny. I added a quote to a thread.

How it started: “anyone who knows this guy is a friend without an introduction”. How’s it going:

I knew Sidney pretty well. I wasn’t a physicist or in his department, but I almost certainly knew him better than any other mathematics PhD student at Harvard. Not enough to be a friend. But enough to call him a teacher and mentor. And a supporter. He was somewhat scary, but suffered anyone gladly who truly wanted to learn.

He was super encouraging about GU but saw symmetry totally differently from my more geometric perspective so there was always a translation issue. He always wanted everything translated into Hilbert space symmetries rather than manifold symmetries. One day he said something uncharacteristically “off” about the Large Exceptional Lie groups: F4 E6 E7 E8. It was uncomfortable because it was a sour note in the middle of an otherwise beautiful explanation. So I called attention to it. He said something like “Do you know something I wish I knew here?” This was a first in our interactions. He clearly knew his perpective which succeeded everywhere else was not working as well here. Or really at all. I explained my view was that we can’t properly intuit the large exceptional groups because they are all “missing” their linear defining representations. He asked “What Real dimensions?” I said that there were missing “phantom representation” modules in dimensions 24, 48, 96, 192. Respectively. He said “What do you mean by that?” So I showed him their homogeneous spaces in dimensions 16, 32, 64, and 128. Respectively. Which clearly do exist. He asked why if they are all projective spaces, that they couldn’t be deprojectivized. And I had to say “They all have classical anomalies. And ‘anomalies’ don’t always need to be canceled. Sometimes they need to be embraced.” And he just smiled and said: “Right. Wow. Got it.” ———— Akshat: I don’t know you. But I thought you would enjoy who Sidney actually was. He was kind, mischievous, brilliant, generous and open. Be well. And good luck.