New pursuit of Schrödinger’s cat | Prospect Magazine: Quantum mechanics is more than a hundred years old, but we still don’t understand it. In recent years, however, physicists have found a fresh enthusiasm for exploring the questions about quantum theory that were swept under the rug by its founders. Advances in experimental methods make it possible to test ideas about why objects on the scale of atoms follow different rules from those that govern objects on the everyday scale. In effect, this becomes an enquiry into the sense in which things exist at all.
In 1900 the German physicist Max Planck suggested that light—a form of electromagnetic waves—consists of tiny, indivisible packets of energy. These particles, called photons, are the “quanta” of light. Five years later Albert Einstein showed how this quantum hypothesis explained the way light kicks electrons out of metals—the photoelectric effect. It was for this, not the theory of relativity, that he won his Nobel prize.