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Many Worlds - Many Minds A view of our universe Ingvar Lindgren Einstein ”God does NOT play dice” Bohr ”God plays dice” Dispute about the interpretation of QM ...modern experiments and the discovery of decoherence have shifted the prevailing quantum interpretations away from wave function collapse towards unitary physics,.... Copenhagen school Bohr, Heisenberg, Pauli Measuring process acc. to Cop. interpret. Result Wave function M i ci i A measurement is performed by a macroscopic apparatus System is instantaneously and randomly transformed to an eigenstate of the observable. Wave function collapse The probability for a certain result is |ci|2 ”God plays dice” Max Born’s probalitity interpretation EPR paradox Einstein-Podolsky-Rosen 1935 J=0 J=0 Two-photon decay Photons of opposite polarization. Acc. to Cop. interpret. the photons have no specific polarization, before the pol. has been measured. Superposition of states. The measurement of photon 1 gives it a specific polarization. Then also the polarization of photon 2 will be given. ci i i Hidden variables? Bell’s inequality Schrödinger’s cat Radiation from a radioactive material initiates a buttet that kills the cat. Before the observation, the cat is acc. to Copenhagen interpret. in a superposition of dead and alive. Superposition -- entanglement ci i Mathematically a state can be expanded in any complete basis set. Entanglement: Coupling of physical states (eigenstates of an observable) ci i i Collapse of wave function: Abrupt destruction of entanglement Problems with the Copenhagen interpretation • The measurement process requires an macroscopic observer. • Artificial border between micro and macro systems. • The collapse of the wave function does not follow any known laws of physics. • Born’s statistical interpretation is an additional assumption that does not follow from the model. Hugh Everett’s interpretation Rev. Mod. Physics 29, 454 (1957) • Dropping collapse of wf Entire world evolves accord. to time-dependent Schrödinger eq. Hugh Everett • Also measuring device treated quantum mechanically (von Neumann) John Wheeler S M |> ( ci |Si>) |M0> No interaction between system and meas. device S M |> ci |SiMi> Interaction between system and meas. device Measuring device affected by interaction with the system under study S 1 M1 S M S2M2 S1M1O1 S M S2M2O1 Observer connected to ONE branch, sees only that branch Everett termed this ”relative-state model” DeWitt introduced around 1970 the term ”Many-worlds interpretation” Why no interference between the branches? The Everett original model is incomplete. Does not explain the emergence of stable, non-interfering brances Does not explain the emergence of classicality Decoherence has to be considered Decoherens (W.H. Zurek, H.D. Zeh ~1980) Zurek, Rev. Mod. Phys. 75, 715 (2003) Dynamical dislocation of quantum-mechanical entanglements, destruction of quantum coherence Wojciech Hubert Zurek Purely quantum-mechanical phenomenon Caused by interaction by the environment Dieter Zeh S1M1 S M S2M2 Left alone, strong coherences between the branches Complete entanglement S1M1 S M S2M2 Interaction with environment S1M1 S M S2M2 Entanglement with environment reduces entanglement between branches S1M1 S M S2M2 Further entanglement with environment reduces further entanglement between branches classicality S1M1 S pointer states stable, decoupled M S2M2 classicality Eventually development of stable pointer states Not further affected by environment Branches completely decoupled Emergence of classicality classicality S1M1 S pointer states stable, decoupled M S2M2 classicality Zurek: Einselection environment-induced superselection Preferred states: Independent of initial conditions classicality S1M1 S pointer states stable, decoupled M S2M2 classicality This is the measurement process in MWI No macroscopic observer No collapse Continuous transition to classicality – No cat! Observer in one branch not aware of the other branches Different “worlds” - different “minds” classicality S1M1 S pointer states stable, decoupled M S2M2 classicality Compare Darwin's theory: Origin of the spicies Survival of the fittest ”Quantum Darvinism” S M S2M2 classicality Copenhagen interpretation: Nature selects randomly ONE branch ”God plays dice” Extra detektor Extra detektor Stern-Gerlach magnet to measure spin orientation Extra detector will destroy interference System (spin) – detector (magnet): = a | s+d+> + b | s-d-> Density matrix r = | > < | = |a|2 | s+d+>< s+d+| +a*b|s+d+>< s-d-|+ba*| s-d->< s+d+| +|b|2 |s-d-> < s-d-| Interference terms System (spin) – detector (magnet) – environment (extra detektor) = a|s+d+ e+ > + b |s-d- e- > Reduced density matrix for sd system (<ei|ej> = dij): rr = e <e| > < |e> = |a|2 | s+d+> < s+d+| + |b|2 | s-d-> < s-d-| No interference H. D. Zeh: The importance of decoherence was overlooked for the first 60 years of quantum theory precisely because entanglement was misunderstood .... Quantum-mechanical decoherence has been verified experimentally Haroche et al, PRL 77, 4887 (1996) Zeilinger et al., Nature 401, 680 (1999) Serge Haroche Anton Zeilinger Advantages with Everett-DeWitt model (with decoherence) Schrödinger equation strictly valid. No collapse of wave function. No classical observer needed. No artificial border between micro and macro systems. Decoherence leads to emergence of classicality – No cat states Born’s statistical interpretation follows from the model (Zurek 2005) Many experts consider this to be the most – or even the only -- consistent interpretation of mechanics quantum presented so far. Dieter Zeh 2000: The multi-universe interpretation (which should rather be called multi-consciousness interpretation) seems to be the only interpretation of a universal quantum theory (with an exact Schrödinger equation) that is compatible with the way the world is perceived. However, because of quantum non-locality it requires an appropriate modification of the traditional epistemological postulate of psycho-physical parallelism. In this interpretation, the physical world is completely described by Everett's wave function that evolves deterministically (Laplacean). This global quantum state then defines an indeterministic (hence "branching") succession of states for all observers. Therefore, the world itself appears indeterministic subjective in principle, but largely objective through quantum correlations (entanglement). Dieter Zeh 2000: ... the Heisenberg-Bohr picture of quantum mechanics is dead. Neither classical concepts, nor any uncertainty relations, complementarity, observables, quantum logic, quantum statistics, or quantum jumps have to be introduced on a fundamental level. Personal view The decoherence leads to disentanglement of entangled states. The branches still exist but are not aware of each other. Universe – a bifurcations tree Universe – a bifurcations tree Universe – a bifurcations tree Universe – a bifurcations tree Universe – a bifurcations tree Universe – a bifurcations tree Life ....... Universe – a bifurcations tree Homo sapiens Life ....... ....... Universe – a bifurcations tree Homo sapiens Life ....... ....... . . . . . . I.L. Universe – a bifurcations tree Homo sapiens Life ....... ....... Probability for Life Hom.sap. I.L extremely small. . . . . . . I.L. Tage Danielssons statistik ”Jag menar, före Harrisburg så var det ju ytterst osannolikt att det som hände i Harrisburg skulle hända, men så fort det hade hänt, rakade ju sannolikheten upp till inte mindre än 100 procent, så det var nästan sant att det hade hänt.” Universe – a bifurcations tree Homo sapiens Life ....... ....... Probability for Life Hom.sap. I.L extremely small. ”Men när det väl har hänt, är sannolikheten 100 %, och det är nästan sant att det har hänt.” . . . . . . I.L. Universe – a bifurcations tree Homo sapiens Life ....... ....... All branches remain – no collapse of wave function . . . . . . I.L. My universe Homo sapiens Life ....... ....... All branches remain – no collapse of wave function But each observer can see only one branch – ”Many minds” . . . . . . I.L. My universe Homo sapiens Life ....... ....... . . . . . . I.L. All branches remain – no collapse of wave function But each observer can see only one branch – ”Many minds” Looks like a collapse of wave function for each observer ”Anthropic principle” Anthropic principle Anthropic principle (Dicke 1961, Brandon Carter, 1973) No coincidence that the universe has the properties it has Brandon Carter Acc. to anthropic principle universe must have exactly these properties in order for humans to be created and to develop If not, we would not exist and could not worry about it. B a r r o w a n d F r a n k , O x fo r d 1 9 8 8 Stephen Hawking A Brief History of Time (1988)9( mill. copies) Universe in a nutshell (2001) Hugh Ross: Fingerprint of God Creator and the Cosmos Martin Rees: Before the beginning Barrow-Silk: The left hand of creation H. Dieter Zeh The direction of time (5.ed.) Knowledge and the world Max Tegmark Commentary Nature 448, 23-24 (5 July 2007) Many lives in many worlds Max Tegmark1 1. Abstract In this Universe, Max Tegmark is a physicist at the Massa chusetts Institute of Technology, Cambridge, Massachusetts, USA. Top of page Accepting quantum physics to be universally true, argues Max Tegmark, means that you should also believe in parallel universes. MIRAGE ENTERPRISES/RGA Is it only in fiction that we can experience parallel lives? If atoms can be in two places at once, so can you. Further reading Zurek, Rev. Mod. Phys. 75, 715 (2003) Zurek, Physics Today 44, 36 (1991) Stanford Encyclopedia of Philosophy D. H. Zeh, arXiv:quant-ph Peter Byrne: The Many Worlds of Hugh Everett, Sci. Amer. Nov. 2007 Tegmark and Wheeler: 100 years of the Quantum, arXiv:quant-ph/0101077v1 I.L. Interpretation of Quantum Mechanics, http://fy.chalmers.se/~f3ail/