„Hullámfüggvény-összeomlás” változatai közötti eltérés
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1. sor:
A [[kvantummechanika]] bizonyos [[A kvantummechanika interpretációi|interpretációiban]] a '''hullámfüggvény összeomlása''' azon két folyamat egyike - a másik a mozgásegyenlet -, ami által a [[kvantumrendszer]]ek a kvantummechanika törvényeinek emgedelmeskednek. Az '''állapotvektor összeomlásának''' is hívják. A hullámfüggvény összeomlásának létét megköveteli:
* a [[koppenhágai interpretáció]] azon verziója, ahol a [[hullámfüggvény]]nek nincs specifikus fizikai jelentése, realitása vagy interpretációja
* az ún. [[tranakciós interpretáció]] ([[John Cramer]])
* egy "spirituális interpretáció, amiben a tudat okozza az összeomlást
Másrészt viszont az összeomlás nem jelenik meg a következő interpretációkban:
* the version of the [[Copenhagen interpretation|Copenhagen interpretation]] where the wavefunction is considered nothing more than a mathematical function with no ''direct'' physical significance
* the interpretation based on [[consistent histories]]
* the [[many-worlds interpretation]]
* the [[Bohm interpretation]].
In general, quantum systems exist in a [[superposition]] of basis states, and evolve according to the time dependent [[Schrödinger equation]], which is one of the two processes mentioned at the beginning of this article - a process included in all interpretations. The contribution of each basis state to the overall wavefunction is called the [[amplitude]]. However, when the wavefunction collapses, which is the other process, from an observer's perspective the state seems to "jump" to one of the basis states and uniquely acquire the value of the property being measured that is associated with that particular basis state.
Upon performing measurement of an [[observable]] ''A'', the probability of collapsing to a particular [[eigenstate]] of ''A'' is [[directly proportional]] to the squared modulus of the (generally [[complex number|complex]]) amplitude associated with it. Hence, in experiments such as the [[double-slit experiment]] each individual [[photon]] arrives at a discrete point on the screen, but as more and more photons are accumulated, they form an interference pattern overall. After the collapse, the system begins to evolve again according to the Schrödinger equation.
The cluster of phenomena described by the expression ''wavefunction collapse'' is a fundamental problem in the interpretation of quantum mechanics known as the [[measurement problem]]. The problem is not really confronted by the [[Copenhagen interpretation]] which simply postulates that this is a special characteristic of the "measurement" process. The [[Everett many-worlds interpretation]] deals with it by discarding the collapse-process, thus reformulating the relation between measurement apparatus and system in such a way that the linear laws of quantum mechanics are universally valid, that is, the only process according to which a quantum system evolves is governed by the Schrödinger equation. Often tied in with the many-worlds interpretation but not limited to it is the physical process of [[decoherence]], which causes an ''apparent'' collapse. Decoherence is also important for the interpretation based on [[Consistent Histories]].
Note that a general description of the evolution of quantum mechanical systems is possible by using [[density matrix|density operators]] and [[quantum operation]]s. In this formalism (which is closely related to the C*-algebraic formalism) the collapse of the wave function corresponds to a non-unitary quantum operation.
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