Robert McNees
Physicist Steven Weinberg was born #OTD in 1933. His 1967 paper "A Model of Leptons" presented a unified theory of the electromagnetic and weak nuclear interactions, and is the most cited paper in particle physics.
Besides his groundbreaking work in particle physics, Weinberg is known for contributions to cosmology and astrophysics, as well as numerous textbooks and popular works.
Image: AIP Emilio Segrè Visual Archives
Robert McNees
Weinberg submitted "A Model of Leptons" to Physical Review Letters in October of 1967. It describes a key component of the Standard Model, and is the most cited particle physics paper in inSPIRE.
His model describes a unified electroweak interaction at high energies. At low energies, spontaneously broken gauge symmetry gives mass to the W and Z bosons, while the photon remains massless. The result is a short range weak force and a long range electromagnetic interaction.
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.19.1264
Robert McNees
“It’s what keeps you going as a theoretical physicist to hope that one of your squiggles will turn out to describe reality.”
They were very good squiggles!
https://home.cern/news/news/cern/50-years-iconic-model-leptons-published
Robert McNees
If you haven't already, I encourage you to read Weinberg's "The First Three Minutes," a beautifully written particle physics history of the Hot Big Bang. If you have, I encourage you to read it again.
It was last updated in 1993, so in some ways it is outdated (inflation, dark energy). But it's a classic. My copy is tattered from re-reading.
Robert McNees
"The First 3 Minutes" opens with a creation story: the frost giant Ymir, the primeval cow Auðumbla, and the yawning void Ginnungagap.
My favorite popularizations of cosmology, whether Norse or modern, all begin with this story.
Robert McNees
He also wrote this in his cosmology textbook. Funny and relatable as a matter-of-fact statement, but also my favorite inadvertent physics humblebrag.
"Look, I tried to recreate the mistakes, but my brain just kept replacing them with the correct results."
Robert McNees
Steven Weinberg passed almost two years ago. He was a towering figure of 20th and 21st century physics and I admired him tremendously. I read his books to pieces, joined his research group at UT-Austin, learned Cosmology from him, graded his courses, read drafts of his textbooks.
Let me share a things he wrote, some of which I've written about at length on here, all of which are worth your time. No attempt to be comprehensive or even representative in what follows!
Robert McNees
First, “What is Quantum Field Theory, and What Did We Think It Is?” A short, personal history of the development of quantum field theory and a lovely explanation of our modern understanding of QFTs as Effective Field Theories.
Robert McNees
That paper is a writeup of a conference talk. There's a remark in there that is always buzzing around in the back of my head when I’m preparing a class or writing a paper.
Robert McNees
“…not just to describe nature, but to explain nature.”
Robert McNees
Next, “The Cosmological Constant Problem.”
Weinberg’s classic review of the catastrophic mismatch between the amount of vacuum energy measured by cosmologists and astronomers, and the predictions made by quantum mechanical theories of particle physics.
Imo this remains one of the most intriguing problem in all of physics. The paper was published about ten years before the discovery of the accelerating Hubble expansion likely driven by a minuscule positive vacuum energy.
https://repositories.lib.utexas.edu/bitstream/handle/2152/61094/Weinberg_1989.pdf
Robert McNees
“Living in the Multiverse”
An opening talk for a conference in which Weinberg confronts the String Landscape and its anthropic implications. “We lose some, and win some.”
One time, when I was in grad school, I asked Weinberg about some point from the anthropic discussion in the 1989 review paper. He gave me a funny look and said that people my age shouldn’t be flirting with anthropic reasoning, we should try to come up with real solutions.
Robert McNees
And finally, this fun little bit from his book “Gravitation and Cosmology.”
A great book, but a common complaint is that it is maybe not the best place to learn GR.
On the other hand, does your favorite GR textbook tackle the really big questions like “Is Middle Earth flat?”
Robert McNees
(Here is my own little humblebrag: The picture above is my copy of the book sitting on my desk. It was given to me by Weinberg when I was his cosmology grader. As a poor grad student I didn't own a copy, I just checked it out of the library. He thought it was crazy that I was grading the course but didn't have a copy of the book, so he took this copy down from his shelf and gave it to me. It's a treasure.)
Robert McNees
Anyway, here is a remembrance of Weinberg in Physics Today, with stories and anecdotes from me, @preskill, and others:
https://pubs.aip.org/physicstoday/Online/5387/Steven-Weinberg-1933-2021
Robert McNees
Oh, and please take just a few minutes to watch this wonderful animated conversation with Weinberg.
Robert McNees
“The effort to understand the universe is one of the very few things that lifts human life a little above the level of farce, and gives it some of the grace of tragedy.”
— Steven Weinberg, The First Three Minutes
Robert McNees
@tb Imo that's an unfair reading of that part of the book. The quote is part of a personal reflection on finding meaning in his work. It isn't denigrating other disciplines so much as trying to find some comfort when confronted with what can feel like a pointlessness of Nature.
ted byfield
@mcnees Disciplinary narcissism. There's no shortage of experts who reflexively condemn the rest of humanity for studying something else or for not studying at all. And there's nothing admirable about it.
Robert McNees
@Smutny I think this book is timeless, because it covers the parts of the history of the universe that were understood to be described by our best physical theories at the time. Those are still our best physical theories. You need other references for important developments since then, like inflation and dark energy.
穆天宁
@mcnees Would you still recommend using this book for studying cosmology, or shall we go for something newer？
Robert McNees
@legendarybassoon Yes! We can see this explicitly. Given four points on a flat plane there are six distinct pairs of points. The distances between them should satisfy a constraint.
Here it is, illustrated with six random points on a 10,000 x 10,000 grid.
Chèvre Mousse
@mcnees Does he find a positive curvature ?
Tolkien lore says that the Earth got round at some point before the Lord of the Rings takes place (but the final resting places of the Elves did not move, so that now it's up in the skies).
Robert McNees
@legendarybassoon Now here is that combination of distances from the map of Middle Earth in the figure. The combination does not vanish, as it must on a flat plane (or cylinder). The surface of Middle Earth is curved.
ted byfield
@mcnees That seems fair, and I'll defer to your expertise — not least for your point that experts are (of course) human like everyone else. That said, it's a real problem when they forget that, something I was thinking about this AM.
https://tldr.nettime.org/@tb/110305059398760859
And thank you for your thoughtful reply, which my own cantankerous one maybe didn't deserve.
Robert McNees
@tb Oh I totally get it. That’s not an unreasonable read of the quote in isolation, I just can't post the whole page as a coda to the thread. Still, a great read if you get a chance.
穆天宁
@mcnees You mean since circa 2008, right？Thanks.
Robert McNees
@Smutny I would say since around 2000. The accelerating Hubble expansion (late 90s) was a profound shift in what we know about the energy content of the Universe. Significant amount of dark energy, rather than none.
Debbie Goldsmith 🏳️⚧️🏳️🌈
@mcnees He was my adviser my first year of grad school (1978-79), but he received the Nobel that academic year (the department threw a party) and got too busy, so I switched to Howard Georgi for my second year. I took GR from Weinberg using his book as the text. I was very sad when he passed away (and Sidney Coleman too, whom I took QFT from).
After my second year I switched out of physics (with an MA) to computers, but I still miss physics.
Debbie Goldsmith 🏳️⚧️🏳️🌈
@mcnees I like this philosophy, which is why it's distressing to see some abandon it in favor of instrumentalism when it comes to the interpretation of quantum mechanics.
Robert McNees
@jrdmb Thank you!
JRDMB
Love this whole Weinberg tribute thread. In many of your OTD posts, you weave in beautiful anecdotes about the quiet, graceful humanity of the person. I find this Weinberg example very touching in his perceptual awareness of the situation that prompted him to gift you the book. Another shining example you told of this kind of perceptual awareness by a prominent person recognizing how a simple act could benefit others is the magnificent Joe Polchinski anecdote at https://twitter.com/mcnees/timelines/805900100862115841
Robert McNees
@dgoldsmith Oh that’s incredible. I took his Cosmo class, but he stopped teaching QFT right before I would have taken it with him. But to be his student! Wow.
Debbie Goldsmith 🏳️⚧️🏳️🌈
@mcnees I wouldn't say that. He was really, really busy, which is why I changed to Prof. Georgi. Also, I was still just doing coursework when he was my advisor (it was my first year). If he'd still been my advisor and I'd gotten into my thesis research, then I would call myself his student. 😊
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