Fall term classes ended yesterday, officially– my last class was Friday– so I’m shifting over to spend more time working on the sequel to How to Teach Physics to Your Dog, which involves talking to Emmy about relativity. Progress has been slower than last time, largely because the previous book was written while I was on sabbatical and before SteelyKid was born. But there’s also a structural issue that’s giving me some problems.
This is partly a matter of familiarity with the material– I’m a low-energy physicist, so I’ve never needed to worry all that much about relativity. A bigger issue, though, is that I’m a low-energy experimental physicist, and that’s better suited to talking about quantum than relativity.
The first book had a very natural structure to it, that fit nicely with the way I engage with science. Every chapter had a discussion of some odd quantum phenomenon, followed by a description of one of the many experiments demonstrating the relevant phenomenon in real systems. This was easy to set up, as there are a whole host of experiments demonstrating quantum effects– interference of matter waves, quantization of light, quantum entanglement, etc. All of these have been done in the real world with familiar atoms and molecules.
Relativity, on the other hand, lacks this kind of convenient experimental support– don’t get me wrong, it’s supported by just about as much experimental evidence as quantum mechanics is. But with a few exceptions, the experimental demonstrations of relativity are not as clean and clear as the experimental demonstrations of quantum phenomena, for a very simple reason: we have never accelerated anything heavier than a single atom to relativistic speeds.
This means that, while the experimental support is there, it’s more subtle, and difficult to pull out in a way that is convincing to a non-physicist human, let alone a dog. There are clear and incontrovertible pictures of molecules behaving like waves, but there aren’t any pictures of moving objects shrinking. We can infer that moving objects must shrink in the direction of motion from things like sea-level cosmic-ray muons, and the fact that time dilation has been directly observed, but that doesn’t have the same impact as a figure showing that fullerene molecules sent through a diffraction grating produce an interference pattern.
It’s not an unsurmountable objection, but it cuts a little against my natural inclination. I’m an empiricist by nature, and strongly prefer to deal in objectively measurable reality, a tendency that has only grown stronger after years of interacting with theorists on the Internet. Demonstrating that relativity is real relies heavily on thought experiments and appeals to mathematical elegance, and I’m much less comfortable with that sort of thing. It’s also harder to plausibly get across to a dog.
I can do it, but it’s a more difficult process for me. In the end, I’ll be better for it– I already see several ways to improve my discussion of relativity the next time I teach our modern physics class. But for the moment, it’s making progress on the book slower than I’d like, leading to more procrastinatory blogging, among other things.
Which reminds me: back to work.