I’m gradually working my way through Lee Smolin’s book The Trouble With Physics (about which I’ll be writing a lot more later), but one thing he wrote in an early chapter gave me a bit of pause. As I’ve noted before, I’m teaching two classes this term that involve quantum mechanics, and one of my peeves is the people who say “don’t try to understand it”. However, Smolin points out something that I was doing without recognizing it—indulging a philosophical bias that doesn’t really work.
You see, I’m a “realist”: I’m someone who thinks there is actually a real world beyond the mathematical models and experiments we perform as part of our scientific research. Many (though not all) of the original developers of quantum mechanics subscribed to a currently-out-of-vogue school of thought called positivism: the only things we can know positively are explored through sensory inputs. Things like electrons don’t have an independent reality because we can’t interact with them directly—it’s simply impossible to do so. Since we as macroscopic beings interact with the microscopic through specialized equipment, it makes no sense to talk about what the electron is doing when we aren’t taking measurements on it. The intellectual leader of this way of thinking was Danish physicist Niels Bohr, so it is generally known as the Copenhagen interpretation of quantum mechanics. Whether realists like it or not, any interpretation of quantum mechanics as it is practiced has to pay lip service to the Copenhagen interpretation; there is no completely satisfactory alternative for realists that can be easily explained in a first quantum mechanics course.
Looking back over my lectures over the last few weeks, I realize I was teaching my students to think about quantum mechanics in a way that’s not exactly compatible with the Copenhagen interpretation. Although I presented the math in the standard way, I was more or less promoting an alternative view known as “hidden variables”, where there is other information not immediately accessed by the experiments. Hidden variables were proposed a long time ago by some of the other developers of quantum mechanics to try to get around the weirdness; there are a lot of constraints on hidden-variable models, but they aren’t all ruled out. And don’t think hidden variables make the weirdness go away entirely—they just move it into another regime that allows us to think electrons and their siblings are real things. The problem is that hidden-variable models aren’t just the same ol’ quantum mechanics, so my approach is necessarily divided between the math and the interpretation of the math.
I’m not exactly sure what the best solution to this situation is from a pedagogical point of view. I know I’m not alone among physicists for paying lip service to the Copenhagen interpretation, borrowing some of its language and concepts, while actually teaching something different. I also know I’m not alone as a realist—without taking a survey or trying to find one (sue me—I’m feeling lazy right now), I would say a lot of my fellow physicists are realists of some stripe or other, though they may not spend a lot of time thinking about the philosophy of quantum mechanics. After all, it’s enough for most people that quantum mechanics works, that it predicts the outcomes of experiments to a high degree of precision, so why worry about the meaning of it? Many students, on the other hand, do want to understand—and from a pedagogical standpoint that’s what I most want from them. The first step for myself may be to be more self-aware, and to make the students aware of my own biases, if only to tell them they need not accept my own spin on the subject and point them to other schools of thought.
(Yes, the title of this post is a reference to The Matrix.)