One world versus many: the inadequacy of Everettian accounts of evolution, probability, and scientific confirmation
Abstract
There is a compelling intellectual case for exploring whether purely unitary quantum theory defines a sensible and scientifically adequate theory, as Everett originally proposed. Many different and incompatible attempts to define a coherent Everettian quantum theory have been made over the past fifty years. However, no known version of the theory (unadorned by extra ad hoc postulates) can account for the appearance of probabilities and explain why the theory it was meant to replace, Copenhagen quantum theory, appears to be confirmed, or more generally why our evolutionary history appears to be Bornrule typical. This article reviews some ingenious and interesting recent attempts in this direction by Wallace, Greaves, Myrvold and others, and explains why they don't work. An account of oneworld randomness, which appears scientifically satisfactory, and has no manyworlds analogue, is proposed. A fundamental obstacle to confirming manyworlds theories is illustrated by considering some toy manyworlds models. These models show that branch weights can exist without having any role in either rational decisionmaking or theory confirmation, and also that the latter two roles are logically separate. Wallace's proposed decision theoretic axioms for rational agents in a multiverse and claimed derivation of the Born rule are examined. It is argued that Wallace's strategy of axiomatizing a mathematically precise decision theory within a fuzzy Everettian quasiclassical ontology is incoherent. Moreover, Wallace's axioms are not constitutive of rationality either in Everettian quantum theory or in theories in which branchings and branch weights are precisely defined. In both cases, there exist coherent rational strategies that violate some of the axioms.
 Publication:

arXiv eprints
 Pub Date:
 May 2009
 arXiv:
 arXiv:0905.0624
 Bibcode:
 2009arXiv0905.0624K
 Keywords:

 Quantum Physics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory;
 Physics  Popular Physics
 EPrint:
 Paper unchanged, but fixed error in previous arxiv submission which caused two identical copies to appear