Editing Schrödinger's cat (section)

=== Many-worlds interpretation ===
{{Main|Many-worlds interpretation}}
[[File:Schroedingers cat film.svg|thumb|The quantum-mechanical "Schrödinger's cat" paradox according to the many-worlds interpretation. In this interpretation, every event is a branch point. The cat is both alive and dead—regardless of whether the box is opened—but the "alive" and "dead" cats are in different branches of the universe that are equally real but cannot interact with each other.]]

In 1957, [[Hugh Everett]] formulated the many-worlds interpretation of quantum mechanics, which does not single out observation as a special process. In the many-worlds interpretation, both alive and dead states of the cat persist after the box is opened, but are [[quantum decoherence|decoherent]] from each other. In other words, when the box is opened, the observer and the possibly-dead cat split into an observer looking at a box with a dead cat and an observer looking at a box with a live cat. But since the dead and alive states are decoherent, there is no communication or interaction between them.

When opening the box, the observer becomes entangled with the cat, so "observer states" corresponding to the cat's being alive and dead are formed; each observer state is [[quantum entanglement|entangled]], or linked, with the cat so that the observation of the cat's state and the cat's state correspond with each other.  Quantum decoherence ensures that the different outcomes have no interaction with each other. Decoherence is generally considered to prevent simultaneous observation of multiple states.<ref name="zurek03">{{cite journal | last1 = Zurek | first1 = Wojciech H. | author-link = Wojciech H. Zurek | year = 2003 | title = Decoherence, einselection, and the quantum origins of the classical | arxiv = quant-ph/0105127 | journal = Reviews of Modern Physics | volume = 75 | issue = 3| page = 715 | doi=10.1103/revmodphys.75.715| bibcode = 2003RvMP...75..715Z | s2cid = 14759237 }}</ref><ref name="zurek91">[[Wojciech H. Zurek]], "Decoherence and the transition from quantum to classical", ''Physics Today'', 44, pp. 36–44 (1991)</ref>

A variant of the Schrödinger's cat experiment, known as the [[Quantum suicide and immortality|quantum suicide]] machine, has been proposed by cosmologist [[Max Tegmark]]. It examines the Schrödinger's cat experiment from the point of view of the cat, and argues that by using this approach, one may be able to distinguish between the Copenhagen interpretation and many-worlds.