Yesterday’s physics education post kicked off a bit of discussion in a place I can’t link to about the usefulness of lectures. Something in that reminded me of an anecdote from my grad school days, that I think is useful, so I’ll post it here.
When we were working on the spin-polarized collision experiment, we expected that a certain effect ought to be pretty big, but when we did the experiment, it didn’t show up at all. We mentioned this in a talk or poster, and a theorist said “Oh, that’s not that surprising.”
We had been pretty surprised, so I was sent off to talk to Paul Julienne, one of the outstanding local theorists, to get an explanation. I went up to Paul’s office, and spent half an hour talking to him about it, and the explanation he gave was perfectly clear, and made total sense.
So, I went back downstairs to Steve Rolston, my immediate supervisor at NIST, and repeated the explanation to him. And somehow, it didn’t make a lick of sense when I said it. Steve poked holes in it immediately, and after five or ten minutes, I didn’t agree with what I had said any more.
After that, Steve went upstairs to talk to Paul, and after half an hour came back downstairs saying he understood it completely. When he repeated the explanation to me, though, it didn’t make any more sense than when I repeated it to him.
We went through a few rounds of this, and never really did get it down until we made Paul come downstairs and spend an hour at the blackboard in the seminar room, where we all hashed it out together. After that, we knew what was going on.
What’s this have to do with lectures and my students’ complaints? Well, far too often, lectures and recitation sessions are just like the conversations Steve and I had with Paul. When somebody else is presenting a detailed explanation of how they solve some problem, it’s very easy to nod along and say “Yes, yes, of course, that’s the thing to do.” You leave the room perfectly convinced that you’ve understood everything, but when you try to apply what you think you know by explaining it to someone else, you find that you didn’t really understand a thing.
(Another example, from my angry QM prof when somebody suggested The Feynman Lectures as a text: “The thing about Feynman is that you read it, and you say ‘Yes! I understand! I’m doing physics!’ then you try to do a problem and you find that, well, you’re not Feynman.”)
My statements about the limited utility of problem-solving in lecture were not intended as a knock on my students, which is why I think this is useful. At the time of this anecdote, I was this close to being a professional scientist– in my fifth year of graduate school in physics. And I still fell into the trap of thinking I understood something just from a verbal explanation.
That’s the problem with good explanations: they’re incredibly seductive, convincing you that you understand things that you don’t understand at all. That’s the logic underlying the active learning methods– making students explain things to each other in class discussions leads to a deeper understanding than just listening to a professor explain the right answer. And that’s why going over problems at the blackboard is so attractive to students– they leave the room thinking they understand how to do the problem– without actually being any help at all.