Everettian quantum mechanics

Everettian quantum mechanics
Name	Everettian quantum mechanics
Founder	Hugh Everett III
Developed	John von Neumann; Paul Dirac; Wolfgang Pauli
Region	United States
Era	20th century
Main interests	Quantum mechanics; Quantum field theory

Everettian quantum mechanics is a formulation of Quantum mechanics originating with Hugh Everett III that posits a universal, unitary Schrödinger equation evolution without collapse. It reframes measurement problem debates by treating measurement interactions as ordinary unitary evolution and introducing a multiplicity of non-communicating effective branches. The approach influenced research at institutions such as Princeton University and Los Alamos National Laboratory and has been discussed by figures including John Bell, David Deutsch, Bryan Skyrms, and Simon Saunders.

Introduction

Everettian quantum mechanics emerged in the mid-20th century as an alternative to the Copenhagen interpretation and was first presented by Hugh Everett III while at Princeton University. Early reception involved critics and supporters from Niels Bohr's circle, Werner Heisenberg, and proponents of decoherence such as H. Dieter Zeh and Wojciech Zurek. The formulation ties into work by John von Neumann on measurement chains, the Dirac formalism, and later rigorous developments in quantum decoherence and quantum information theory led by groups at Harvard University, Caltech, and University of Oxford.

Formulation and Key Principles

Core principles include universal applicability of the Schrödinger equation, rejection of a special collapse postulate, and reliance on decoherence processes studied by H. Dieter Zeh and Wojciech Zurek to produce effectively classical records. Formalists reference mathematical structures developed by Paul Dirac, John von Neumann, and Eugene Wigner while linking to technical treatments from Roger Penrose and work in quantum field theory contexts by Steven Weinberg and Richard Feynman. The formulation uses Hilbert space methods common to John von Neumann and operational considerations advanced at Bell Labs and IBM Research.

Interpretation of Measurement and Branching

Measurements are modeled as unitary interactions producing entangled states between system and apparatus, a viewpoint that contrasts with collapse proposals advanced by Max Born and debated by Niels Bohr. Branching arises via environmentally induced decoherence as articulated by Wojciech Zurek and formalized by H. Dieter Zeh; this connects to experiments at CERN, MIT, and Stanford University probing macroscopic superpositions. Proponents like David Deutsch and Simon Saunders argue that branching yields effective classical histories akin to those discussed in Everett's thesis and elaborated in panels at Royal Society meetings and conferences at Perimeter Institute.

Ontology: Worlds, Wavefunction, and Reality

Ontology centers on the universal wavefunction described in the language of Paul Dirac and John von Neumann with debates about whether branches constitute distinct "worlds" as suggested by Hugh Everett III or merely emergent patterns defended by David Wallace. Discussions draw on metaphysical analyses related to positions taken by Hilary Putnam and David Lewis and institutional debates at universities such as University of Cambridge and Princeton University. Competing ontologies consider realism about the wavefunction as advocated by John Bell and alternatives influenced by Niels Bohr-style instrumentalism explored at University of Copenhagen.

Relation to Probability and Decision Theory

Everettian accounts address probability using approaches from decision theory advanced by Leonard Savage and adapted by David Deutsch and David Wallace to derive the Born rule. Debates invoke Bayesian frameworks from Bruno de Finetti and frequentist perspectives represented historically by Richard von Mises and contemporary critics such as Simon Saunders and Adrian Kent. Discussions have occurred in venues including Institute for Advanced Study seminars and publications associated with Cambridge University Press and Oxford University Press.

Comparisons with Other Interpretations

Everettian mechanics is compared with the Copenhagen interpretation, collapse models like those proposed by Ghirardi–Rimini–Weber proponents and Philip Pearle, hidden-variable theories such as de Broglie–Bohm theory and advocates like David Bohm, and relational or information-theoretic approaches linked to Carlo Rovelli and Christopher Fuchs. It contrasts with objective collapse proposals discussed at Perimeter Institute workshops and with pragmatist lines associated with Niels Bohr and later commentators at University of Chicago.

Criticisms and Open Problems

Criticisms include the preferred basis problem engaged by H. Dieter Zeh and Wojciech Zurek, the origin of the Born rule questioned by Adrian Kent and Tim Maudlin, and concerns about ontology and parsimony raised by Occam's razor-influenced commentators such as John Searle and critics in journals from American Physical Society publications. Open problems involve extending the account to quantum gravity contexts debated by researchers at CERN, Perimeter Institute, and Institute for Advanced Study, reconciling with thermodynamic irreversibility as discussed by Ludwig Boltzmann-inspired scholars, and clarifying empirical distinctions from collapse or hidden-variable alternatives highlighted in experiments at LIGO and NIST.

Category:Interpretations of quantum mechanics