What Is Real?: The Unfinished Quest for the Meaning of Quantum Physics

by Adam Becker

Bryce DeWitt, Wheeler’s colleague, fellow quantum cosmologist, and co-organizer of the Chapel Hill quantum gravity conference, was skeptical of Everett’s thesis at first. “I am afraid that it is precisely at the most crucial point in Everett’s argument where many people, including myself, will be unable to swallow your implication.… What I am not prepared to accept” is the branching of worlds required by Everett’s theory, wrote DeWitt to Wheeler. “I can testify to this from personal introspection, as can you. I simply do not branch.” Wheeler passed DeWitt’s reply on to Everett; in his reply, Everett drew an analogy between DeWitt’s objection and early objections to the Copernican Sun-centered model of the solar system, tinged with his usual irony: One of the basic criticisms leveled against the Copernican theory was that “the mobility of the earth as a real physical fact is incompatible with the common sense interpretation of nature.” In other words, as any fool can plainly see the earth doesn’t really move because we don’t experience any motion. However, a theory which involves the motion of the earth is not difficult to swallow if it is a complete enough theory that one can also deduce that no motion will be felt by the earth’s inhabitants (as was possible with Newtonian physics). Thus, in order to decide whether or not a theory contradicts our experience, it is necessary to see what the theory itself predicts our experience will be. Now in your letter you say, “… I simp...