A lot of people have been blogging and Twittering about this subway map of science, which puts various branches of science in the place of the lines on the London Underground map, showing connections between them. It’s a huge graphic, but a kind of cool image.
I do, however, have a problem with it, which is illustrated by the key to the lines shown at right. The category of physics is presented as “Theoretical Physics and Quantum Mechanics.” I have no problem with the quantum part, as quantum mechanics is one of the greatest intellectual achievements in human history. I do have a problem with the theoretical part, though.
“Theoretical Physics” is not a synonym for “Physics.” It’s at most half the story, and probably less, because without experiment, there is no theory. Without Michael Faraday, who had no great aptitude for mathematics, there would be no Maxwell’s Equations. without Ernest Rutherford’s scattering experiments, there would be no Bohr model for hydrogen (Bohr was actually working for Rutherford at the time). Without Heinrich Hertz and Robert Millikan, Einstein wouldn’t've gotten the Nobel for his model of the photoelectric effect, which was in many ways his most revolutionary contribution to physics. Without Albert Michelson and Edward Morley and their attempt to measure the aether, relativity might’ve taken a very different form. And so on.
Now, the map includes a lot of these people, so this is mostly a problem of labeling, rather than the gigantic oversight I thought at first (Faraday’s name is on the opposite side of the physics line from all the others, so I initially thought he’d been left out entirely). But you encounter this sort of thing all the time– people speak of theoretical physics as if it were the whole of physics, and that’s nowhere near being true. Modern theoretical physics could not exist without experimental physics, and to the extent that there is a crisis in physics today (as you often hear), it’s a crisis that comes from an excess of theory and an under-supply of experiment.
You can’t have one of these without the other. Any map of the path to modern science needs experimentalists just as much, if not more, than it needs theorists.