New pursuit of Schrödinger’s cat
Quantum theory is reliable but fraught with paradox. Philip Ball asks if scientists will now find an object existing in two places at once
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.
The 1927 Solvay conference on particle physics: back row, third from right, Werner Heisenberg, sixth from right, Erwin Schrödinger; middle row, from right, Niels Bohr, Max Born, Louis de Broglie and centre, Paul Dirac. Front row, second from left, Max Planck, next to him, Marie Curie, then Hendrik Lorentz and Albert Einstein. Of the 29 pictured, 18 won Nobel prizes, Curie in both physics and chemistry