ed that we human beings are radioac- tive, it shocked me. I was in high school listening to a lecture by the re- markable polymath and astrophysicist Tommy Gold, who had done pioneering work in cosmology, pulsars, and lunar science, and he in- formed us that the particles that made up most of the mass of our

so that a small shift in the mass of the former, when embedded in nuclei, means it can no longer decay into the latter. That is what I learned from Tommy Gold. It still amazes me when I think about it. The existence of complex matter, the periodic table, everything we see, from distant stars to the keybo