Changes

==Multiverse hypotheses in physics==

==Multiverse hypotheses in physics==

[[Laura Mersini|Laura Mersini-Houghton]] claims that the [[WMAP cold spot#Parallel universe|WMAP cold spot]] may provide testable empirical evidence for a parallel universe within the multiverse. According to [[Max Tegmark]], (Scientific American, 2003, May, Parallel Universes) the existence of other universes is a direct implication of cosmological observations. Tegmark describes the set of related concepts which share the notion that there are universes beyond the familiar observable one, and goes on to provide a taxonomy of parallel universes organized by levels. (Parallel Universes [http://www.wintersteel.com/files/ShanaArticles/multiverse.pdf])

[[Laura Mersini|Laura Mersini-Houghton]] claims that the [[WMAP cold spot#Parallel universe|WMAP cold spot]] may provide testable empirical evidence for a parallel universe within the multiverse. According to [[Max Tegmark]], (Scientific American, 2003, May, Parallel Universes) the existence of other universes is a direct implication of cosmological observations. Tegmark describes the set of related concepts which share the notion that there are universes beyond the familiar observable one, and goes on to provide a taxonomy of parallel universes organized by levels. (Parallel Universes [https://www.wintersteel.com/files/ShanaArticles/multiverse.pdf])

===Classification===

===Classification===

In order to clarify terminology, [[George Ellis]], U. Kirchner and W. R. Stoeger recommend using the term "the Universe" for the theoretical model of the whole of the causally [[topology|connected]] [[spacetime]] in which we live, '''universe domain''' for the observable universe or a similar part of the same space-time, "universe" for a general space-time, either our own "Universe" or another one disconnected from our own, '''multiverse''' for a [[set]] of disconnected space-times, and '''multi-domain universe''' to refer to a model of the whole of a single connected space-time in the sense of [[chaotic inflation]] models.

In order to clarify terminology, [[George Ellis]], U. Kirchner and W. R. Stoeger recommend using the term "the Universe" for the theoretical model of the whole of the causally [[topology|connected]] [[spacetime]] in which we live, '''universe domain''' for the observable universe or a similar part of the same space-time, "universe" for a general space-time, either our own "Universe" or another one disconnected from our own, '''multiverse''' for a [[set]] of disconnected space-times, and '''multi-domain universe''' to refer to a model of the whole of a single connected space-time in the sense of [[chaotic inflation]] models.

====Multiverses (Ellis, Koechner and Stoeger sense)====

====Multiverses (Ellis, Koechner and Stoeger sense)====

'''Level III:''' ([[Hugh Everett|Hugh Everett III]]'s [[many-worlds interpretation]]) An interpretation of [[quantum mechanics]] that proposes the existence of multiple universes, all of which are "identical", but exist in possibly different states. It is widely believed that Everett's interpretation (considered as a formal theory) is a [[conservative extension]] of standard quantum mechanics – that is, as far as results expressible in the language of ordinary quantum mechanics are concerned, it leads to no new results. This, according to Tegmark, "is ironic given that this level has historically been the most controversial".  In September 2007 [[David Deutsch]] presented what is considered a proof of the many-worlds interpretation. [http://www.breitbart.com/article.php?id=paUniverse_sun14_parallel_universes&show_article=1&cat=0 Breitbart.com, Parallel universes exist - study, Sept 23 2007]

'''Level III:''' ([[Hugh Everett|Hugh Everett III]]'s [[many-worlds interpretation]]) An interpretation of [[quantum mechanics]] that proposes the existence of multiple universes, all of which are "identical", but exist in possibly different states. It is widely believed that Everett's interpretation (considered as a formal theory) is a [[conservative extension]] of standard quantum mechanics – that is, as far as results expressible in the language of ordinary quantum mechanics are concerned, it leads to no new results. This, according to Tegmark, "is ironic given that this level has historically been the most controversial".  In September 2007 [[David Deutsch]] presented what is considered a proof of the many-worlds interpretation. [https://www.breitbart.com/article.php?id=paUniverse_sun14_parallel_universes&show_article=1&cat=0 Breitbart.com, Parallel universes exist - study, Sept 23 2007]

====Ultimate ensemble====

====Ultimate ensemble====

===Many worlds interpretation of quantum physics===

===Many worlds interpretation of quantum physics===

[[Hugh Everett]]'s [[many-worlds interpretation]] (MWI) is one of several mainstream [[Interpretation of quantum mechanics|interpretations of quantum mechanics]]. Other interpretations include the [[Copenhagen interpretation|Copenhagen]] and the [[consistent histories]] interpretations. The multiverse proposed by MWI has a shared time parameter. In most formulations, all the constituent universes are structurally identical to each other and though they have the same physical laws and values for the fundamental constants, they may exist in different states. The constituent universes are furthermore non-communicating, in the sense that no information can pass between them, although in Everett's formulation they may potentially affect each other.

[[Hugh Everett]]'s [[many-worlds interpretation]] (MWI) is one of several mainstream [[Interpretation of quantum mechanics|interpretations of quantum mechanics]]. Other interpretations include the [[Copenhagen interpretation|Copenhagen]] and the [[consistent histories]] interpretations. The multiverse proposed by MWI has a shared time parameter. In most formulations, all the constituent universes are structurally identical to each other and though they have the same physical laws and values for the fundamental constants, they may exist in different states. The constituent universes are furthermore non-communicating, in the sense that no information can pass between them, although in Everett's formulation they may potentially affect each other.

''Tegmark, Max,'' [http://www.arxiv.org/abs/quant-ph/9709032/] The Interpretation of Quantum Mechanics: Many Worlds or Many Words?], 1998. To quote: "What Everett does NOT postulate: ''"At certain magic instances, the world undergoes some sort of metaphysical 'split' into two branches that subsequently never interact."'' This is not only a misrepresentation of the MWI, but also inconsistent with the Everett postulate, since the subsequent time evolution could in principle make the two terms...interfere. According to the MWI, there is, was and always will be only one wavefunction, and only decoherence calculations, not postulates, can tell us when it is a good approximation to treat two terms as non-interacting."</ref> through [[quantum interference]].

''Tegmark, Max,'' [https://www.arxiv.org/abs/quant-ph/9709032/] The Interpretation of Quantum Mechanics: Many Worlds or Many Words?], 1998. To quote: "What Everett does NOT postulate: ''"At certain magic instances, the world undergoes some sort of metaphysical 'split' into two branches that subsequently never interact."'' This is not only a misrepresentation of the MWI, but also inconsistent with the Everett postulate, since the subsequent time evolution could in principle make the two terms...interfere. According to the MWI, there is, was and always will be only one wavefunction, and only decoherence calculations, not postulates, can tell us when it is a good approximation to treat two terms as non-interacting."</ref> through [[quantum interference]].

''Deutsch, David, [http://www.qubit.org/people/david/Articles/Frontiers.html David Deutsch's Many Worlds], ''Frontiers'', 1998.'' The state of the entire multiverse is related to the states of the constituent universes by [[quantum superposition]], and is described by a single [[universal wavefunction]]. Related are [[Richard Feynman]]'s [[multiple histories]] interpretation and [[H. Dieter Zeh]]'s [[many-minds interpretation]].  

''Deutsch, David, [https://www.qubit.org/people/david/Articles/Frontiers.html David Deutsch's Many Worlds], ''Frontiers'', 1998.'' The state of the entire multiverse is related to the states of the constituent universes by [[quantum superposition]], and is described by a single [[universal wavefunction]]. Related are [[Richard Feynman]]'s [[multiple histories]] interpretation and [[H. Dieter Zeh]]'s [[many-minds interpretation]].  

Many worlds interpretation cannot explain the apparently [[Fine-tuned universe]]. The physical constants of all the "many worlds" are the same. Many worlds interpretation can, however explain the apparent improbability of a planet like [[Earth]] existing. See [[Rare Earth hypothesis]]. If the Many worlds interpretation is true there are so many copies of our universe that the existence of at least one planet like Earth is not surprising.

Many worlds interpretation cannot explain the apparently [[Fine-tuned universe]]. The physical constants of all the "many worlds" are the same. Many worlds interpretation can, however explain the apparent improbability of a planet like [[Earth]] existing. See [[Rare Earth hypothesis]]. If the Many worlds interpretation is true there are so many copies of our universe that the existence of at least one planet like Earth is not surprising.

To postulate an infinity of unseen and unseeable universes just to explain the one we do see seems superficially contrary to [[Occam's Razor]].

To postulate an infinity of unseen and unseeable universes just to explain the one we do see seems superficially contrary to [[Occam's Razor]].

Tegmark answers:"A common feature of all four multiverse levels is that the simplest and arguably most elegant theory involves parallel universes by default. To deny the existence of those universes, one needs to complicate the theory by adding experimentally unsupported processes and ad hoc postulates: [[finite space]], [[Wavefunction collapse|wave function collapse]] and [[ontological asymmetry]]. Our judgment therefore comes down to which we find more wasteful and inelegant: many worlds or many words." [http://www.elfis.net/phorum/read.php]

Tegmark answers:"A common feature of all four multiverse levels is that the simplest and arguably most elegant theory involves parallel universes by default. To deny the existence of those universes, one needs to complicate the theory by adding experimentally unsupported processes and ad hoc postulates: [[finite space]], [[Wavefunction collapse|wave function collapse]] and [[ontological asymmetry]]. Our judgment therefore comes down to which we find more wasteful and inelegant: many worlds or many words." [https://www.elfis.net/phorum/read.php]

Thus, according to Tegmark, paradoxically the multiverse scenario is more parsimonious than that of a single universe.

Thus, according to Tegmark, paradoxically the multiverse scenario is more parsimonious than that of a single universe.

===Other objections===

===Other objections===

The entire range of multiverse hypotheses, with specific emphasis on Hugh Everett's many-worlds interpretation, have been criticised by proponents of [[intelligent design]]. [[William Dembski]] in particular, derides it as inflating explanatory resources without evidence or warrant, and terms such concepts "[[inflaton]]s".[http://www.iscid.org/papers/Dembski_ChanceGaps_012002.pdf]

The entire range of multiverse hypotheses, with specific emphasis on Hugh Everett's many-worlds interpretation, have been criticised by proponents of [[intelligent design]]. [[William Dembski]] in particular, derides it as inflating explanatory resources without evidence or warrant, and terms such concepts "[[inflaton]]s".[https://www.iscid.org/papers/Dembski_ChanceGaps_012002.pdf]

===Anthropic principle===

===Anthropic principle===

===Trans-world identity===

===Trans-world identity===

A metaphysical issue that crops up in multiverse schema that posit infinite identical copies of any given universe is that of the notion that there can be identical objects in different possible worlds. According to the [[counterpart theory]] of [[David Lewis]], the objects should be regarded as similar rather than identical.<ref>[http://plato.stanford.edu/archives/sum2002/entries/identity-relative/ Deutsch, Harry, "Relative Identity", The Stanford Encyclopedia of Philosophy (Summer '02), Edward N. Zalta (ed.)]</ref><ref>[http://www.scils.rutgers.edu/~kantor/601/Ex_1Overview.html Paul B. Kantor "The Interpretation of Cultures and Possible Worlds", 1 October 2002]</ref>

A metaphysical issue that crops up in multiverse schema that posit infinite identical copies of any given universe is that of the notion that there can be identical objects in different possible worlds. According to the [[counterpart theory]] of [[David Lewis]], the objects should be regarded as similar rather than identical.<ref>[https://plato.stanford.edu/archives/sum2002/entries/identity-relative/ Deutsch, Harry, "Relative Identity", The Stanford Encyclopedia of Philosophy (Summer '02), Edward N. Zalta (ed.)]</ref><ref>[https://www.scils.rutgers.edu/~kantor/601/Ex_1Overview.html Paul B. Kantor "The Interpretation of Cultures and Possible Worlds", 1 October 2002]</ref>

==Virtual realities as a multiverse==

==Virtual realities as a multiverse==

Christianity, Judaism and Islam all incorporate parts of this idea to explain the existence of three separate realities (Heaven, Hell and Earth) all existing simultaneously. The Christian Bible, Islamic Koran and Hebrew Torah all cite examples of heaven, hell and earth existing since the beginning of recorded time.

Christianity, Judaism and Islam all incorporate parts of this idea to explain the existence of three separate realities (Heaven, Hell and Earth) all existing simultaneously. The Christian Bible, Islamic Koran and Hebrew Torah all cite examples of heaven, hell and earth existing since the beginning of recorded time.

===Hindu universes===

===Hindu universes===

The earliest known records describing the concept of a multiverse are found in ancient [[Hindu cosmology]], in texts such as the [[Puranas]]. They expressed the idea of an infinite number of universes, each with its own gods, inhabitants and planets, and an infinite cycle of births, deaths, and rebirths of a universe, with each cycle lasting 8.4 billion years. The belief is too that the number of universes are infinite.<ref>[[Carl Sagan]], Placido P D'Souza (1980s). [http://www.rediff.com/news/jan/29sagan.htm Hindu cosmology's time-scale for the universe is in consonance with modern science.]; Dick Teresi (2002). ''Lost Discoveries : The Ancient Roots of Modern Science&nbsp;– from the Babylonians to the Maya''.</ref>

The earliest known records describing the concept of a multiverse are found in ancient [[Hindu cosmology]], in texts such as the [[Puranas]]. They expressed the idea of an infinite number of universes, each with its own gods, inhabitants and planets, and an infinite cycle of births, deaths, and rebirths of a universe, with each cycle lasting 8.4 billion years. The belief is too that the number of universes are infinite.<ref>[[Carl Sagan]], Placido P D'Souza (1980s). [https://www.rediff.com/news/jan/29sagan.htm Hindu cosmology's time-scale for the universe is in consonance with modern science.]; Dick Teresi (2002). ''Lost Discoveries : The Ancient Roots of Modern Science&nbsp;– from the Babylonians to the Maya''.</ref>

==Fictional multiverses==

==Fictional multiverses==

==References==

==References==

[http://www.internet-encyclopedia.org/index.php/Criticism_of_Many_worlds_in_one Criticism of Many worlds in one]

[https://www.internet-encyclopedia.org/index.php/Criticism_of_Many_worlds_in_one Criticism of Many worlds in one]

[http://www.breitbart.com/article.php?id=paUniverse_sun14_parallel_universes&show_article=1&cat=0 Parallel universes exist - study]

 

[https://www.breitbart.com/article.php?id=paUniverse_sun14_parallel_universes&show_article=1&cat=0 Parallel universes exist - study]

==See also==

==See also==

==External links==

==External links==

* [http://cerncourier.com/cws/article/cern/31860 Physics in the Multiverse], published by [[Aurélien Barrau]] in the CERN Courier

* [https://cerncourier.com/cws/article/cern/31860 Physics in the Multiverse], published by [[Aurélien Barrau]] in the CERN Courier

* [http://xxx.lanl.gov/abs/quant-ph/0104033 Preprint] of David Deutsch's paper ''The Structure of the Multiverse''

* [https://xxx.lanl.gov/abs/quant-ph/0104033 Preprint] of David Deutsch's paper ''The Structure of the Multiverse''

* [http://www.bbc.co.uk/science/horizon/2001/parallelunitrans.shtml BBC Horizon -Parallel Universes]

* [https://www.bbc.co.uk/science/horizon/2001/parallelunitrans.shtml BBC Horizon -Parallel Universes]

* [http://www.hedweb.com/manworld.htm#believes Michael Price's Everett FAQ]

* [https://www.hedweb.com/manworld.htm#believes Michael Price's Everett FAQ]

* [http://arxiv.org/PS_cache/gr-qc/pdf/9703/9703089.pdf Against Many-Worlds Interpretations] Adrian Kent, The Institute for Advanced Study, School of Natural Sciences, Princeton, New Jersey

* [https://arxiv.org/PS_cache/gr-qc/pdf/9703/9703089.pdf Against Many-Worlds Interpretations] Adrian Kent, The Institute for Advanced Study, School of Natural Sciences, Princeton, New Jersey

* [http://arxiv.org/PS_cache/astro-ph/pdf/0407/0407329.pdf Multiverses and Cosmology: Philosophical Issues] W. R. Stoeger1,, G. F. R. Ellis, and U. Kirchner. Department of Mathematics and Applied Mathematics, University of Cape Town; Vatican Observatory Research Group, Steward Observatory, The University of Arizona, Tucson, Arizona

* [https://arxiv.org/PS_cache/astro-ph/pdf/0407/0407329.pdf Multiverses and Cosmology: Philosophical Issues] W. R. Stoeger1,, G. F. R. Ellis, and U. Kirchner. Department of Mathematics and Applied Mathematics, University of Cape Town; Vatican Observatory Research Group, Steward Observatory, The University of Arizona, Tucson, Arizona

* [http://arxiv.org/ftp/astro-ph/papers/0403/0403047.pdf Mulitverse Cosmological Models] by P.C.W. Davies

* [https://arxiv.org/ftp/astro-ph/papers/0403/0403047.pdf Mulitverse Cosmological Models] by P.C.W. Davies

* [http://www.weidai.com/everything.html The 'Everything' mailing list (and archives), A "discussion of the idea that all possible universes exist".]

* [https://www.weidai.com/everything.html The 'Everything' mailing list (and archives), A "discussion of the idea that all possible universes exist".]

*[http://thoughtcast.org/casts/the-end-of-our-universe-among-other-timely-topics Interview with Tufts cosmologist Alex Vilenkin] on his new book, "Many Worlds in One: The Search for Other Universes" on the podcast and public radio interview program [http://www.thoughtcast.org ThoughtCast.]

*[https://thoughtcast.org/casts/the-end-of-our-universe-among-other-timely-topics Interview with Tufts cosmologist Alex Vilenkin] on his new book, "Many Worlds in One: The Search for Other Universes" on the podcast and public radio interview program [https://www.thoughtcast.org ThoughtCast.]

* [http://www.upstream.nl/comments.php?id=751_0_1_0_C Joseph Pine II about Multiverse], Presentation at Mobile Monday Amsterdam, 2008

* [https://www.upstream.nl/comments.php?id=751_0_1_0_C Joseph Pine II about Multiverse], Presentation at Mobile Monday Amsterdam, 2008

[[Category: Cosmology]]

[[Category: Cosmology]]

[[Category:Physical Cosmology]]

[[Category:Physical Cosmology]]