Memorial Day Physics

 

Cambridge University Press 2023. It's a nice volume, already with my pencil markings, and coffee stains on the last few pages. Baptized, as my French friend Jean would say. The books I use look used.

Spent Memorial Day bashing my head against a physics topic which is arguably the most advanced topic in theory, and upon which the validity so much of current particle physics depends. It's called renormalization, and the book I was reading today is called, fittingly enough Renormalization. It was published only in 2023. It's from Cambridge University Press, which is a great publisher for physics monographs and makes high volume books. I acquired it because it was recommended by ChatGPT for my self-study course for next year's conference.

I won't bother to explain what "renormalization" means beyond saying it's a very sophisticated way to remove unwanted infinities in one's models of particle physics that would otherwise invalidate the entire theory (because you can prove anything if you allow infinities).  By these sophisticated processes, which some dissenters think are sleight of hand, or even fraudulent, one can arrive at predictions---supposedly.

This is what I have to master if I'm going to useful in my field. I would not be attempting this without ChatGPT to help me, but with AI, I flip into the mode where I am convinced I can understand anything if I approach it the right way.

I have several modes for studying a physics subject from a book---top down, or word-by-word.  Both are appropriate at various times. In this case, it turns out the author provided an initial introductory chapter of only three pages long (!) that summarizes the entire subject. This is a dream, to have this. So I am going word for word, understanding everything in those three pages. Literally that will halve the entire effort in learning this topic. That's the thing I realized about word-for-word. It's not necessary for the entire book. But if the introduction is good enough, that's all you need to learn word-for-word. The rest maybe you can do top down, once you get down the introduction.

Unfortunately most books don't have introductions like that. But this one does. 

I was taking notes from the book out on the porch. I'd go out for a half hour and push ahead another sentence or two, taking notes on a piece of 11x14 card stock. Then I would take a break before returning later. I would look at my pencil notes and erase and rewrite them to suit my understanding, and make them more concise. 

Most importantly, I have set the process in motion. I can get up tomorrow morning and while drinking coffee, I can push ahead another sentence in the intro. Then I lean back in my rocking chair and review the whole thing, putting the new information into place with the other parts I know.

By the end of the week, I want to be able to teach a course on this subject. I have wildly unrealistic expectations of my own abilities that way, but even if I fall short of such a goal, I will have gotten very far. And the knowledge will stay with me, even if I don't retain all the details. A year from now I can open up this book and I will read that introduction. It will be almost obvious, everything in it. 

Although the book is new, and in many ways cutting edge, it's interesting to note that the material in it is over forty years old. That's how much physics has been stuck for decades. In fact I first remember reading about the "renormalization group", a topic within renormalization itself, thirty years ago as a graduate student. I had pulled out an advanced text from the library which was an anthology of papers from a recent conference on the subject. I saw there was an article written by the great Steve Weinberg on the subject of the renormalization group. I got only half a paragraph into it before being hopelessly overwhelmed. But I remembered that in the opening sentence, he had made a joke, because Weinberg was that way. He stated that the first law of conservation of information is that "you can't get anywhere by grinding equations."

It's a joke of course, a play on real conservation laws (like ones for energy and momentum). But even then I understood what it meant. It meant that to discover new physics, you need to do more than perform mathematical tricks. You need to bring new insight into the mathematics. 

I mention this because it was no long after that when I ran into Weinberg into faculty mailroom. I was in there using the departmental copier for my course (illicitly, as it happens). I had been in there and in walks the great Weinberg, so it's just me and him in this little room. I think to myself, "I've got to say something to him". Into my head pops that incomprehensible article about the renormalization group from his chapter of that anthology book. So I look at him and address him like a colleague, out of the blue, with all the confidence I can muster:

"Is it true that the first law of conservation of information is that you can't get anywhere by grinding equations?"

He cracks a big smile and chuckles. Then he goes off with his mail. It was my moment with the great Weinberg. I took his year long course on quantum field theory, but this was the only private moment I ever had with the man. 

One thing about me is that I never give up on anything. It may take me decades, but I keep going. Now I am on the verge of actually understanding the renormalization group. Weinberg passed away four years ago. It is up to me to be his legacy, and the legacy of all the other great minds I knew then. If not me, who?