Many-Worlds Interpretation of Quantum Theory  

In General > s.a. locality.
* Idea: Each of the possible histories that contributes to the quantum amplitude for a process really exists, so the wave function is a '"physical thing" and provides a complete description of the system; Relatively conservative interpretation, although it is not very intuitive and has some conceptual problems.
* Advantage: It does not need a wave-function-collapse postulate, and avoids the measurement problem by considering every term in a quantum superposition as actual; With its elegant treatment of apparent wave function "collapse," it set the stage for applications of quantum theory such as decoherence, quantum computing, and quantum information.
* Probability issue: If a history branches into finitely many possibilities (like an electron branching into two outcomes of a Stern-Gerlach experiment) and each branch is "real," what does it mean to say that it is more or less likely than another? Why doesn't the simple counting measure work? If there are infinitely many branches and any given one has probability zero, why is it there at all? Some proposals have been made.
* Branching issue: How does the branching work in a covariant view?
* History: 1957, initially proposed in the PhD dissertation of Hugh Everett III, a student of Wheeler's, as the "relative state" formulation of quantum mechanics, for quantum cosmology, because of difficulties with the standard interpretation (Wheeler later changed his mind), and based on a frequentist interpretation of probabilities; Resurrected by DeWitt in 1970 and refined by Hartle, who related the probabilities to an inner product structure; 1995, Saunders and the relationship between amplitudes and probabilities; 1999, Deutsch and decision theory approach to deal with the issue of probabilities.
* And literature: It appears in short stories by Borges, and in F Hoyle's October the First Is Too Late (and in Star Trek).

Phenomenology > s.a. quantum computing; semiclassical quantum mechanics [including macroscopic objects].
@ General references: Zeh FP(73)qp/03 [and the København interpretation]; Plaga FP(97)qp/95; Page qp/99 [consequences].
@ Cosmology: Yurov & Yurov ht/05; Aguirre & Tegmark PRD(11)-a1008 [infinite universe]; Bousso & Susskind PRD(12)-a1105 [and the multiverse]; Barrau EJTP-a1412; > s.a. multiverse cosmology; quantum cosmology.
@ And experiment: Deutsch in(86); Yun a1405 [double slit]; Gerig a1406 [proposed tests]; Deutsch a1508 [elimination of probabilistic concepts]; Päs IJQF-a1609 [probe in psychology?].

References > s.a. hidden variables; measurement in quantum theory [including quantum field theory].
@ General: Everett RMP(57); Wheeler RMP(57); DeWitt in(68); Cooper & van Vechten AJP(69)dec; DeWitt & Graham ed-73; Everett in(73); Geroch Nous(84); Healey Nous(84); Smolin in(84); Stein Nous(84); Mukhanov in(85); Whitaker JPA(85); Fraïssé HPL(87); Tegmark FdP(98)qp/97 [vs others]; Ben-Dov AJP(90)sep; Wallace SHPMP(02)qp/01 [world-view], SHPMP(03)qp/01 [and indefiniteness]; issue Nat(07)jul [50th anniversary]; Saunders et al ed-10; Barrett & Byrne ed-12; Marchildon SHPMP(15)-a1504 [spectrum of opinions]; Chen a1504 [mathematical formalism]; Sudbery in(06)-a1601; Boughn a1801; Parrochia a2001 [meaning]; Wu a2005 [tutorial]; Saunders a2103 [branching structure, and decoherence].
@ History: Allori et al BJPS(11)-a0903 [Schrödinger's first quantum theory as a precursor].
@ And the Born rule: Hanson PRS(06) [mangled worlds scenario]; Rae SHPMP(09)-a0810; Carroll & Sebens ch(14)-a1405 [derivation]; Drezet a2011.
@ Probabilities, other: Ballentine FP(73) [re derivation of statistical postulate]; Tappenden BJPS(00); Vaidman qp/01-conf; Wallace SHPMP(03), BJPS(06); Rubin FP(03); Saunders in(05)qp/04; Van Wesep AP(06)qp/05 [all phenomenological features of quantum observation are derivable from the many-worlds premise]; Price qp/06; Wallace BJPS(06), SHPMP(07) [satisfactory]; Lewis SHPMP(07) [uncertainty cannot be the ground for probability]; Baker SHPMP(07) [Deutsch-Wallace argument is circular]; Hemmo & Pitowsky SHPMP(07) [unsatisfactory]; Price a0802-conf [criticism of Deutsch-Wallace]; Blood a0901; Simon a0908 [conscious observers]; Sudbery AIP(11)-a1009; Blood a1107; Hsu MPLA(12)-a1110 [intro]; Wilson BJPS(13) [avoiding the incoherence problem]; Saunders a1609-in [chance]; Mandolesi a1704; Tappenden Syn-a1911; Barrett SHPMP-a1912; Tappenden qRep(19)-a1912; Saunders ch-a2103.
@ Basis problem: Ben-Dov FPL(90); Stapp CJP(02)qp/01.
@ In support: Chalmers (96); Vaidman qp/96; Sakaguchi gq/97; Vaidman qp/00; Tipler qp/00 [and locality]; Tegmark Nat(07)-a0707; Saunders & Wallace BJPS(08), comment Tappenden BJPS(08), reply BJPS(08) [branching and diverging, meaning of uncertainty]; Tappenden BJPS(11); Bevers SHPMP(11); Wallace in(10)-a1111 [many worlds as emergent from the underlying theory through decoherence]; Duhamel & Raymond-Robichaud a1111; Page a1212 [theological argument]; Vaidman a1602-proc; Frauchiger & Renner nComm(18)-a1604, Brukner Ent(18)-a1804, comments Salom a1809, Lazarovici & Hubert a1809 [no-go results on single-world interpretations], Boge a1909, Bub a2008; Carroll 19; Wilson a2007; Tipler a2105 [inequivalent to standard quantum theory]; > s.a. bell's theorem.
@ Against: Wheeler in(86); Kent IJMPA(90)gq/97; Byrne & Hall PhSc(99); Singh IJMPD(08)-a0705 [falsified by quantum gravity non-linearity]; Kent in(10)-a0905 [attempts at coherent accounts of probability]; Blood a1010 [fatally flawed]; Jeknić-Dugić et al a1012; Schwindt a1210; Edlam SHPMP(14)-a1504 [incoherence, the problem of confirmation]; Drezet a1502; Bub a1804 ["single-world" interpretation]; Varshovi a2011 [ontological perspective].
@ And pilot-wave interpretation: Ben-Dov NCB(90); Valentini in(10)-a0811, comment Brown a0901.
@ And modal interpretation: Domenech et al JMP(09)-a0904 [formal comparison].
@ Related topics: Squires FPL(88) [and paranormal effects]; Barvinsky & Kamenshchik G&C(95) [symmetries]; Rubin FPL(04)qp/03 [no basis ambiguity]; Van Esch qp/05 [wave-function collapse]; Rubin FP(06) [spatial degrees of freedom]; Mallah a0902 [re quantum immortality and quantum suicide]; Mitra a0902-FQXi [changing the past by forgetting]; Bondoni a1006-wd [concept of possibility]; Bradley BJPS(11) [and measurement]; Carter in(11)-a1203 [classical limit, and the anthropic principle]; Zeh NQ-a1211 [role of the observer]; Marchildon proc-a1704 [and spacetime]; > s.a. anthropic principle.
> Online resources: Wikipedia page; Stanford Encyclopedia of Philosophy page.

@ Many-minds: Donald qp/97, qp/99; Zeh FPL(00)qp/99; Hemmo & Pitowsky BJPS(03)qp/01 [probability and non-locality].
@ Many interacting worlds: Hall et al PRX(14)-a1402 + news nat(14)oct; Sturniolo a1709 [computational applications].
@ Other: Squires EJP(87) [many views of one world]; Mallah a0709 ["many computations"]; Page a1102 ["many perceptions"]; Conroy SHPMP(12) [relative-facts interpretation]; Aerts & Sassoli de Bianchi FS(15)-a1406 ["many measurements"]; Suarez a1712 ["all-possible-worlds", a unified reformulation of many-worlds and Copenhagen]; 't Hooft a1904-conf [Ontology Conservation Law].

main pageabbreviationsjournalscommentsother sitesacknowledgements
send feedback and suggestions to bombelli at – modified 23 may 2021