Abstract

“Is there anyone who hasn’t heard about the strange fate of Schrödinger’s cat? I doubt it! But just in case, I shall start this talk by reviewing how Schroedinger’s thought-experiment about an infernal device designed to kill a cat, if a radioactive atom decays, raises fundamental issues about understanding quantum theory. Then I shall discuss one radical approach, which has just had its fiftieth anniversary: Everett’s proposal that there is no funny business about a measurement process inducing the quantum state to collapse indeterministically, according to which of the alternative outcomes occurs; and there is no supplementing of the state (traditionally called ‘hidden variables’) so as to represent which outcome occurs—or indeed to represent any other physical fact.

For this proposal to reconcile its uncollapsed and un-supplemented quantum state with the apparent fact that any quantum experiment has a single outcome, it needs to identify the Appearances—our apparent macroscopic realm, with its various experiments’ outcomes—with one of a vast multiplicity of realms, called ‘branches’. Indeed, a dizzying vision. Is it true?”

Dr. Jeremy Butterfield is a philosopher of physics at the University of Cambridge, and a fellow of Trinity College. His research includes philosophical aspects of quantum theory, relativity theory and classical mechanics.