From Light to Starlight
During my final year at high school our physics teacher, Mr. Taylor (Mr. Taylor also ran the truly excellent school astronomical society) told us that, despite the fact that by that stage we’d learned a lot about electromagnetic waves and photons, at the end of the day physics could not actually say exactly what light is. This is, of course, true, but remarkably it doesn’t matter (well, it might matter to a philosopher), provided we accept two very important things about physics. First, what we generally call the great theories of physics, such as classical electromagnetic theory and quantum mechanics, are in fact models, which physicists use to try and explain as best they can the results of experiments and hopefully to predict the results of future experiments. Second, while it is often the case that one theory or model (in this case quantum theory and photons) supersedes an earlier one (the idea of electromagnetic waves), the older theory is very often still extremely useful.