The job of physicists is to worry about numbers, but one number has perplexed physicists for more than a century. That number is 0.00729735256—approximately 1/137. This is the fine-structure constant. It appears everywhere in the equations of quantum physics. The fine-structure constant, designated by the Greek letter alpha (α), is one of the many constants of nature that power our laws of physics, like the speed of light, the gravitational constant, or Planck’s constant. These constants can have different values depending upon which system of units are used to express them. For instance, the speed of light in vacuum is...