I’ve been hard at work in recent months on a new textbook on electromagnetic waves, and that has led me to dig deep into understanding a number of subjects, and their history, that I have only really casually considered in the past. One topic that jumped out at me is the phenomenon of so-called “anomalous” dispersion. This name indicates that it is different from “normal” dispersion, which is the phenomenon that causes a prism to break up white light into a rainbow, as illustrated on Pink Floyd’s Dark Side of the Moon album cover:
In a prism, the angle at which light is refracted by the glass depends on the frequency of light, i.e. its color. In normal dispersion, the higher frequency light (blue and violet) is refracted more strongly than the lower frequency light (red and yellow). In anomalous dispersion, roughly the opposite happens: lower frequencies are refracted more than higher frequencies!
I thought it would be fun to talk a bit about the history of anomalous dispersion, which gets at some of the physics of matter, and also allows me to share lots of pretty pictures taken by Robert Williams Wood, who studied the phenomenon in the early 1900s!
Continue reading
Skulls in the Stars 