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The ''relative state'' formulation is due to , Quantum Mechanics and Reality, ''Physics Today'',23(9) pp 30-40 (1970) also April 1971 letters followup , On the Interpretation of Measurement in Quantum Theory, ''Foundation of Physics'', vol. 1, pp. 69-76, (1970). Wojciech Hubert Zurek , Decoherence and the transition from quantum to classical, ''Physics Today'', vol. 44, pp. 36-44, (1991). Wojciech Hubert Zurek , Decoherence, einselection, and the quantum origins of the classical, ''Reviews of Modern Physics'', 75, pp 715-775, (2003) becoming quite popular, taken as a class overall. MWI is one of many Multiverse hypotheses in Physics and Philosophy . It is currently considered a mainstream interpretation along with the other decoherence interpretations and the Copenhagen Interpretation . OUTLINE Although several versions of MWI have been proposed since which the Copenhagen Interpretation proposes. The exact form of the Quantum dynamics modelled, be it the non-relativistic Schrödinger Equation , Relativistic Quantum Field Theory or some form of Quantum Gravity or String Theory , does not alter the content of MWI since MWI is a Metatheory applicable to all Quantum Theories and hence to all credible fundamental theories of physics. MWI's main conclusion is that the universe (or Multiverse in this context) is composed of a Quantum Superposition of very many, possibly Infinite ly many, increasingly divergent, non-communicating parallel universes or quantum worlds. The idea of MWI originated in Everett's Princeton Ph.D. thesis "The Theory of the Universal Wavefunction", developed under his thesis advisor John Archibald Wheeler , a shorter summary of which was published in 1957 entitled "Relative State Formulation of Quantum Mechanics" (Wheeler contributed the title "relative state"; John Archibald Wheeler , ''Geons, Black Holes & Quantum Foam'', ISBN 0-393-31991-1. pp 268-270 Everett originally called his approach the "Correlation Interpretation"). The phrase "many worlds" is due to Bryce DeWitt , who was responsible for the wider popularisation of Everett's theory, which had been largely ignored for the first decade after publication. DeWitt's phrase "many-worlds" has become so much more popular than Everett's "Universal Wavefunction" or Everett-Wheeler's "Relative State Formulation" that many forget that this is only a difference of terminology; the content of all three papers is the same. The many-worlds interpretation shares many similarities with later, other "post-Everett" interpretations of quantum mechanics which also use , which it assigns to the wavefunction, and it has the minimal formal structure possible, rejecting any Hidden Variables , Quantum Potential , any form of a collapse postulate (i.e. Copenhagenism ) or mental postulates (such as the Many-minds Interpretation makes). Many worlds is often referred to as a Theory , rather than just an interpretation, by those who propose that many worlds can make testable predictions or that all the other, non-MWI, are inconsistent, illogical or unscientific in their handling of measurements; Hugh Everett argued that his formulation was a Metatheory , since it made statements about other interpretations of quantum theory; that it was the "only completely coherent approach to explaining both the contents of quantum mechanics and the appearance of the world" {Link without Title} . WAVEFUNCTION COLLAPSE AND THE PROBLEM OF INTERPRETATION As with the other interpretations of quantum mechanics, the many-worlds interpretation is motivated by behavior that can be illustrated by the Double-slit Experiment . When Particles Of Light (or anything else) are passed through the double slit, a calculation assuming wave-like behavior of light is needed to identify where the particles are likely to be observed. Yet when the particles are observed in this experiment, they appear as particles (i.e. at definite places) and not as non-localized waves. The Copenhagen Interpretation of quantum mechanics proposed a process of " Collapse " in which an indeterminate quantum system would probabilistically collapse down onto, or select, just one determinate outcome to "explain" this phenomenon of observation. Wavefunction collapse was widely regarded as artificial and ad-hoc, so an alternative interpretation in which the behavior of measurement could be understood from more fundamental physical principles was considered desirable. Everett's Ph.D. work provided such an alternative interpretation. Everett noted that for a composite system (for example that formed by a particle interacting with a measuring apparatus, or more generally by a subject (the "observer") observing an object (the "observed" system) the statement that a subsystem (i.e. the observer or the observed) has a well-defined state is meaningless -- in modern parlance the subsystem states have become Entangled -- we can only specify the state of one subsystem ''relative'' to the state of the other subsystem, i.e. the state of the observer and the observed are correlated. This led Everett to derive from the unitary, deterministic dynamics alone (i.e. without assuming wavefunction collapse) the notion of a ''relativity of states'' of one subsystem relative to another. Everett noticed that the unitary, deterministic dynamics alone decreed that after an observation is made each element of the to Werner Heisenberg , objecting to placing observables at the heart of the new quantum mechanics, during Heisenberg's 1926 lecture at Berlin; related by Heisenberg in 1968, quoted by Abdus Salam , ''Unification of Fundamental Forces'', Cambridge University Press (1990) ISBN 0-521-37140-6, pp 98-101 .) Since Everett stopped doing research in theoretical physics shortly after obtaining his Ph.D., much of the elaboration of his ideas was carried out by other researchers and forms the basis of much of the Decoherent approach to Quantum Measurement . ADVANTAGES # MWI removes the observer-dependent role in the Quantum Measurement process by replacing Wavefunction Collapse with Quantum Decoherence . Since the role of the observer lies at the heart of most, if not all, "quantum paradoxes" this automatically resolves a number of problems; see for example Schrödinger's Cat Thought-experiment , the EPR Paradox , von Neumann's "boundary problem" and even Wave-particle Duality . Quantum Cosmology also becomes intelligible, since there is no need anymore for an observer outside of the universe. # MWI allows quantum mechanics to become a Realist , Deterministic , Local theory making it more akin to Classical Physics (including the Theory Of Relativity ). # MWI (or other, broader Multiverse considerations) provides a context for the Anthropic Principle which may provide an explanation for the Fine-tuned Universe . #MWI, being a Decoherent formulation, is axiomatically more streamlined than the Copenhagen and other Collapse interpretations; and thus favoured under certain interpretations of Ockham's Razor . Of course there are other decoherent interpretations that also possess this advantage with respect to the collapse interpretations. OBJECTIONS
::MWI response: the decoherence or "splitting" or "branching" is complete when the Measurement is complete. In Dirac Notation a measurement is complete when: | ||
| :The Probability Of An | "http://wwwinformationdelightinfo/information/entry/observable" class="copylinks">Observable <math>A</math> to have the value <math>a</math> in a normalized state <math> \psi
angle</math> is the absolute square of the eigenvalue component of the state corresponding to the eigenvalue a: <math>P(a) = \langle a \psi
angle ^2</math> |
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