On this day in 1892, the great physicist Arthur Compton was born. He was primarily interested in high energy particles and light and how they interacted with matter. For example, he showed that JJ Thomson was right and that x-rays scattered by the first 16 elements of the periodic table were polarized. He did extensive work on cosmic rays, showing that there were more at the poles than elsewhere. He correctly deduced that they were charged particles being changed by the earth’s magnetic field. He was also very important in the Manhattan Project.
Compton is most known, of course, for the Compton Effect. This is very similar to the Photoelectric Effect. What Compton noticed and explained was that x-rays scattered by free electrons change wavelengths — reducing their energy. This is notable because it showed that photons were acting like particles. Generally, light is absorbed or not. Similarly, a particle can have part of its energy reduced by a collision. The Compton effect shows that light can do the same thing.
After the war, Arthur Compton went on to head Washington University in St Louis where he oversaw the liberalization of the school. Under him, the university was desegregated in 1952. But it is unclear how much credit he should get for that. He retired at 62 and died of a cerebral hemorrhage at the age of 69.
Like a lot of scientists of his time, he was very interested in the subject of free will. He pushed the idea of free will as a two stage process and thought that quantum indeterminacy made actions “free.” This is nonsense. I don’t believe in free will at all, and I find attempts to prove it pathetic. The two-stage model is just a fancy way to tap dance around the issue. But in this way, Compton is like Newton: outside of the confines of science, he was lost in a sea of magic thinking. This is not to put him down. The fact that he grappled with these questions at all makes him much more serious than most people — scientists especially.
Happy birthday Arthur Compton!