Column: All the physics I used to know

When I started graduate school in the fall of 1999, the candidacy exam, still a year in the future, already loomed large. If you’ve been to physics grad school, you’re likely familiar with the comprehensive exams that are a feature of most programs; Sankar Das Sarma has more to say about them in his commentary for the March issue. I’d chosen a school that didn’t have a policy of deliberately flunking out a certain portion of its students once a year of useful TA labor had been extracted from them. But even without those high stakes, my classmates and I knew we were in for an intense experience: three full days of written tests followed by a 45-minute grilling by a panel of professors.

Miller’s Diary

Physics Today editor Johanna Miller reflects on the latest Search & Discovery section of the magazine, the editorial process, and life in general.

Older students advised us that the exam would mark the global maximum in the amount of physics we knew—a transition, if you will, between a state of net learning and one of net forgetting. In my naïveté, I didn’t quite believe them. I’d spent my whole life so far taking progressively advanced classes, and I could hardly imagine that the knowledge base I was building wasn’t going to be there forever.

Of course, the older students were right and I was wrong. Once I turned the bulk of my attention from classwork to research, everything not immediately useful for my lab work started slipping away. In the spring of my fourth year, I took time out of the lab to take a class on many-body theory. (We were required for graduation to take a couple of high-level classes outside our area of expertise, and that, believe it or not, was the least unsuitable of my options.) I was baffled. I knew those equations would once have meant something to me, but not anymore. Fortunately, the professor was patient. I gave a presentation where I mumbled some things about Kosterlitz–Thouless theory and vortex pairing, and she let me get back to my experiments.

In 2009, a few years into my career at Physics Today, I was asked to review an early draft of a feature article on solid-state nuclear magnetic resonance . There was one section, on average Hamiltonian theory, that I couldn’t make heads or tails of, and I said as much in my review. My senior colleague (now editor-in-chief) Charles Day also reviewed the article; of the same section he said, “I like this section. . . . Any readers who remember basic quantum mechanics should grasp the essential approach.”

I often think back to that incident—conclusive proof that I don’t remember basic quantum mechanics!—especially when I’m writing about a quantum-heavy topic, as I did this month with my story on long-distance spin exchange in an atomic cloud . As a writer and editor, I need to strike an unusual balance between knowing a little about a lot and knowing a lot about a little. In any given month, I might find myself writing about astronomy, optics, geoscience, or biophysics. Admittedly, I’ll never know as much about any of those fields as the researchers who work in them every day, because I don’t have the luxury of single-mindedly focusing on any one field at the expense of all the others. Our reader surveys consistently show that many of you turn to Physics Today to keep a broad perspective on areas of physics other than your own, perhaps because you, too, tend to forget the things you don’t use every day.

Although I don’t retain everything from every story I’ve ever written, remnants of my accumulated knowledge base are still there. For a 2016 story about a new development in solid-state NMR, I drew on what I learned about the technique from the 2009 feature article—and was rewarded with a phone call from one of the principal investigators, who was convinced that I had a research background in the field. Note, however, that average Hamiltonian theory makes no appearance in that story.