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The multiverse (or meta-universe, metaverse) is the hypothetical set of multiple possible universes (including our universe) that together comprise everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. The term was coined in 1895 by the American philosopher and psychologist William James.[1] The different universes within the multiverse are sometimes called parallel universes.
The structure of the multiverse, the nature of each universe within it and the relationship between the various constituent universes, depend on the specific multiverse hypothesis considered. Multiverses have been hypothesized in cosmology, physics, astronomy, philosophy, transpersonal psychology and fiction, particularly in science fiction and fantasy. In these contexts, parallel universes are also called "alternative universes", "quantum universes", "interpenetrating dimensions", "parallel dimensions", "parallel worlds", "alternative realities", and "alternative timelines", among others.

Contents

Multiverse hypotheses in physics

Tegmark's classification

Cosmologist Max Tegmark has provided a taxonomy of universes beyond the familiar observable universe. The levels according to Tegmark's classification are arranged such that subsequent levels can be understood to encompass and expand upon previous levels, and they are briefly described below.[2][3]

Level I: Beyond our cosmological horizon

A generic prediction of cosmic inflation is an infinite ergodic universe, which, being infinite, must contain Hubble volumes realizing all initial conditions.
An infinite universe should contain an infinite number of Hubble volumes. All will have the same physical laws and physical constants. However, almost all will be different from our Hubble volume regarding configurations such as how matter is distributed in the volume. But since there are an infinite number of such volumes, then some of these will be very similar or even identical to our own. Thus, far beyond our cosmological horizon, there will eventually be a Hubble volume identical to our own. Tegmark estimates that such an identical volume should be about 10(10115) (larger than a googolplex) meters away.[4][5]

Level II: Universes with different physical constants

"Bubble universes", every disk is a bubble universe (Universe 1 to Universe 6 are different bubbles, they have physical constants that are different from our universe), our universe is just one of the bubbles.
In the chaotic inflation theory, a variant of the cosmic inflation theory, the multiverse as a whole is stretching and will continue doing so forever, but some regions of space stop stretching and form distinct bubbles, like gas pockets in a loaf of rising bread. There exists an infinite number of such bubbles which are embryonic level I multiverses of infinite size. Different bubbles may experience different spontaneous symmetry breaking resulting in different properties such as different physical constants.[4]
This level also includes John Archibald Wheeler's oscillatory universe theory and Lee Smolin's fecund universes theory.

Level III: Many-worlds interpretation of quantum mechanics

Hugh Everett's many-worlds interpretation (MWI) is one of several mainstream interpretations of quantum mechanics. In brief, one aspect of quantum mechanics is that certain observations cannot be predicted absolutely. Instead, there is a range of possible observations each with a different probability. According to the MWI, each of these possible observations corresponds to a different universe. Suppose a die is thrown that contains 6 sides and that the result corresponds to a quantum mechanics observable. All 6 possible ways the die can fall correspond to 6 different universes. (More correctly, in MWI there is only a single universe but after the "split" into "many worlds" these cannot in general interact.)[6]
Tegmark argues that a level III multiverse does not contain more possibilities in the Hubble volume than a level I-II multiverse. In effect, all the different "worlds" created by "splits" in a level III multiverse with the same physical constants can be found in some Hubble volume in a level I multiverse. Tegmark writes that "The only difference between Level I and Level III is where your doppelgängers reside. In Level I they live elsewhere in good old three-dimensional space. In Level III they live on another quantum branch in infinite-dimensional Hilbert space." Similarly, all level II bubble universes with different physical constants can in effect be found as "worlds" created by "splits" at the moment of spontaneous symmetry breaking in a level III multiverse.[4]
Related to the many-worlds idea are Richard Feynman's multiple histories interpretation and H. Dieter Zeh's many-minds interpretation.

Level IV: Ultimate Ensemble

The Ultimate Ensemble hypothesis of Tegmark himself. This level considers equally real all universes that can be defined by mathematical structures. This also includes those having physical laws different from our observable universe. Tegmark writes that "abstract mathematics is so general that any TOE that is definable in purely formal terms (independent of vague human terminology) is also a mathematical structure. For instance, a TOE involving a set of different types of entities (denoted by words, say) and relations between them (denoted by additional words) is nothing but what mathematicians call a set-theoretical model, and one can generally find a formal system that it is a model of." He argues this "it implies that any conceivable parallel universe theory can be described at Level IV" and "it subsumes all other ensembles, therefore brings closure to the hierarchy of multiverses, and there cannot be say a Level V."[7]
Jürgen Schmidhuber, however, says the "set of mathematical structures" is not even well-defined, and admits only universe representations describable by constructive mathematics, that is, computer programs. He explicitly includes universe representations describable by non-halting programs whose output bits converge after finite time, although the convergence time itself may not be predictable by a halting program, due to Kurt Gödel's limitations.[8][9][10] He also explicitly discusses the more restricted ensemble of quickly computable universes.[11]

Cyclic theories

The Cyclic Universe
In several theories there is a series of infinite, self-sustaining cycles (for example: an eternity of Big Bang-Big crunches).

M-theory

A multiverse of a somewhat different kind has been envisaged within the multi-dimensional extension of string theory known as M-theory.[12] In M-theory our universe and others are created by collisions between p-branes in a space with 11 and 26 dimensions (the number of dimensions depends on the chirality of the observer)[13][14]; each universe takes the form of a D-brane[13][14]. Objects in each universe are essentially confined to the D-brane of their universe, but may be able to interact with other universes via gravity, a force which is not restricted to D-branes[15]. This is unlike the universes in the "quantum multiverse", but both concepts can operate at the same time.

Anthropic principle

The concept of other universes has been proposed to explain why our universe seems to be fine-tuned for conscious life as we experience it. If there were a large number (possibly infinite) of different physical laws (or fundamental constants) in as many universes, some of these would have laws that were suitable for stars, planets and life to exist. The weak anthropic principle could then be applied to conclude that we would only consciously exist in those universes which were finely-tuned for our conscious existence. Thus, while the probability might be extremely small that there is life in most of the universes, this scarcity of life-supporting universes does not imply intelligent design as the only explanation of our existence.

WMAP cold spot

Laura Mersini-Houghton claims that the WMAP cold spot may provide testable empirical evidence for a parallel universe within the multiverse.

Criticisms

Non-scientific claims

Critics claim that many of these theories lack empirical testability, and without hard physical evidence are unfalsifiable; outside the methodology of scientific investigation to confirm or disprove.

Occam's Razor

Tegmark answers: "A skeptic worries about all the information necessary to specify all those unseen worlds. But an entire ensemble is often much simpler than one of its members. This principle can be stated more formally using the notion of algorithmic information content. The algorithmic information content in a number is, roughly speaking, the length of the shortest computer program that will produce that number as output. For example, consider the set of all integers. Which is simpler, the whole set or just one number? Naively, you might think that a single number is simpler, but the entire set can be generated by quite a trivial computer program, whereas a single number can be hugely long. Therefore, the whole set is actually simpler. Similarly, the set of all solutions to Einstein's field equations is simpler than a specific solution. The former is described by a few equations, whereas the latter requires the specification of vast amounts of initial data on some hypersurface. The lesson is that complexity increases when we restrict our attention to one particular element in an ensemble, thereby losing the symmetry and simplicity that were inherent in the totality of all the elements taken together. In this sense, the higher-level multiverses are simpler. Going from our universe to the Level I multiverse eliminates the need to specify initial conditions, upgrading to Level II eliminates the need to specify physical constants, and the Level IV multiverse eliminates the need to specify anything at all." He continues "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, wave function collapse and ontological asymmetry. Our judgment therefore comes down to which we find more wasteful and inelegant: many worlds or many words. Perhaps we will gradually get used to the weird ways of our cosmos and find its strangeness to be part of its charm."[4][16][17]

Multiverse hypotheses in philosophy and logic

Modal realism

Possible worlds are a way of explaining probability, hypothetical statements and the like, and some philosophers such as David Lewis believe that all possible worlds exist, and are just as real as the actual world (a position known as modal realism).[18]

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.[19][20]

Fictional realism

The view that because fictions exist, fictional characters exist as well. There are fictional entities, in the same sense as that in which, setting aside philosophical disputes, there are people, Mondays, numbers and planets.[21][22]

Fate and the multiverse

Hugh Everett's many-worlds interpretation (MWI), information theory, chaotic inflation theory, as well as the double-slit experiment, point to a multiverse, consisting of an infinite number of verses, inside a finite space. Being that "we" are all inside a finite space, the infinite number of universes are overlapping each other. This could be the reason for the wave function of particles. The Many Worlds Interpretation states, in brief, "one aspect of quantum mechanics is that certain observations cannot be predicted absolutely. Instead, there is a range of possible observations each with a different probability. According to the MWI, each of these possible observations corresponds to a different universe." Each universe has a set of physical rules, but also a set of plans. If "each possible observation corresponds to a different universe" that means, in one universe "A" happened, in another "B" happened, and so on. Each universe has a different set of eventualities that reside within. Given an infinite number of universes, a copy of any given eventuality is bound to exist. This means, not only is there a universe where I am writing this page, there is a universe where I am not writing this page. There is a universe where I am still a child. There is a universe where I have yet to be born. There is a universe where I am typing this page, exactly word for word, error for error. Max Tegmark estimates that such an identical volume should be about 10(10115) meters away. This measure of distance sprouts from an older hypothesis, where our universe is inside an infinite space. The space cannot be infinite. If space were infinite, the universes would never overlap, and wave function would not be a part of this cosmos. Any given eventuality is "played out" on any given universe. Follow this eventuality far enough, and the question of the idea of fate will enter. If I roll a die, and get (for instance) two, there is another universe where I rolled and got a three. Another where I rolled and got a one, etc. etc. Every eventuality is "played out." This means that the universe in which we reside, has a given set of physical rules, and only a given set of eventualities. If I roll the die and get a four, for example, I have essentially "taken" that eventuality. If I roll a four in this cosmos, theoretically, there are a number of other cosmos' that can no longer roll and get four. What happens, happens because that is what was going to happen in this universe. If we had choice, there would be an inordinate number of universes with rich people, because most will choose to be rich, for example. You may have lost your job in this universe, but you are now the boss in another. Superposition poses a threat to this theory. One can argue that our universe (and therefore everything inside it) is in a state of superposition, created at the Big Bang. We were entangled at that moment, and that state only collapses when an outside force interacts with it. In the double-slit experiment, when shooting only one photon at a time, the particle is truly in a state of superposition until something tries to observe it. When not observed, it acts like a wave. When observed, it will act like a particle. Our cosmos (and everything inside) may be in a state of superposition, wherein, interacting with it, collapses the state of superposition, and creates a unique reality.

Multiverse hypotheses in religion and spirituality

Islam

There are exactly seven verses in the Quran that specify that there are seven heavens. One verse says that each heaven or sky has its own order, possibly meaning laws of nature. Another verse says after mentioning the seven heavens "and similar earths".
Fakhr al-Din al-Razi (1149-1209), in dealing with his conception of physics and the physical world in his Matalib, "explores the notion of the existence of a multiverse in the context of his commentary" on the Qur'anic verse, "All praise belongs to God, Lord of the Worlds." He raises the question of whether the term "worlds" in this verse refers to "multiple worlds within this single universe or cosmos, or to many other universes or a multiverse beyond this known universe." Al-Razi rejected the Aristotelian and Avicennian view of the impossibility of multiple universes. He describes the main Aristotelian arguments against the existence of multiple universes, pointing out their weaknesses and refuting them. This rejection arose from his affirmation of atomism, as advocated by the Ash'ari school of Islamic theology, which entails the existence of vacant space in which the atoms move, combine and separate.[23]

Planes of existence

Certain religions and esoteric cosmologies propound the idea of a whole series of subtle emanated planes or worlds.

Afterlife

Many religions include an afterlife existence in realms, such as heavens and hells, which may be very different from the observable universe.

Eschatology

Eschatological scenarios may include a new different world after the end time of the current one. For example, Hindu cosmology include the idea of an infinite cycle of births and deaths and an infinite number of universes with each cycle lasting 8.4 billion years.[24]
Similar eschatological scenarios appear in other religions, in the form of belief in there being a new and different world after the end time of the current one.

Multiverse hypothesis in fiction

Fiction by definition does not claim to be a completely accurate description of our observable universe. All fiction could thus be seen as describing different universes. Some genres, such as crime fiction and historical fiction, may describe universes similar to the observable one, while others, such as fantasy, science fiction, and alternate history, may describe ones more different.
Parallel universes in fiction may interact. For example, in science fiction a common plot device is hyperspace which is temporarily entered and used for faster than light travel.

Literature

The term 'Multiverse' was notably used in 1962 by science fiction author Michael Moorcock, though not for the first time in literature, having previously been used by both William James in 1895 and John Cowper Powys in his 1955 novel The Brazen Head (p. 279). The author and editor Paul le Page Barnett, best known by the pseudonym John Grant, later used the term 'polycosmos' for a similar concept binding together a number of his works. He formed the word from Greek morphemes where 'multiverse' uses Latin.[25]
In the World of Tiers novels (1965) by Philip José Farmer, the background of the stories are set in a multiverse where godlike beings are able to create a number of 'pocket universes' at their whim. Our own universe is part of this series, but interestingly its boundary appears to end at the edge of the solar system.
In a 1971 short story titled 'All The Myriad Ways', author Larry Niven explores the psychological implications of 'Multiverse' theory. The story somewhat erroneously postulates that since a split in the Multiverse is created at each decision point, the number of suicides would rise dramatically as people consider how the possibility of ending their lives would impact the many versions of the universe. The idea is that simply considering the act causes all possible outcomes to occur in somewhat equal proportion. While the story is highly entertaining, this notion is pure fiction, and is not supported by any significant theory of muitiple universes.
The way in which Robert A. Heinlein used interlocking characters and settings in his novels have led to his worlds being described as a multiverse.[26]
In C.S. Lewis's series The Chronicles of Narnia, multiple universes exist within a monotheistic, rather than a naturalistic framework. At the will of Aslan (who corresponds to the Christian God), the main characters enter different universes through various means, including a forest containing pools of water. A leap into any pool will take one into a universe with natural laws and even a structure differing from our own. (In Narnia, for instance, the world is not spherical, but flat, and the brave mouse Reepicheep travels to the end of it in order to enter "Aslan's Country.").
In Philip Pullman's trilogy His Dark Materials the lead characters enter parallel universes by using a knife to cut into the fabric of reality.
The novel Timeline by Michael Crichton uses the multiverse theory as a mechanism for travel back to medieval times to research the Hundred Years' War.

Film

In the 2001 Jet Li film, The One, Jet Li's character travels to several different universes to carry out his deadly deeds.
Although not explicitly described as such in the film, the alternate reality experienced by the George Bailey and Clarence characters in the 1946 film It's a Wonderful Life may be interpreted as an alternate universe.

Television

The 2010 season of the television show Lost features a parallel universe. A hydrogen bomb explodes on the island changing the history of the main characters. In this scenario, the survivors of Oceanic Flight 815 never crash on the island. However, the first scenario continues to play out as well, thus creating a parallel universe.
In the network movie Turtles Forever, The 2003 turtles meet their 1980's conterparts, claiming that they came from an alternate universe. It is later revealed that there is a Multiverse of the Teenage Mutant Ninja Turtles.
The television show Sliders was based entirely on the possibility of parallel universes. In each episode the stars experienced an alternate universe through the use of a device that would create a portal through which to travel to those alternate realities.
In the season 8 premiere of the comedy television show Family Guy, Stewie and Brian use an enhanced device to travel to different universes. They temporarily stay in a world where dogs are the dominant species before returning to their world.
The FOX primetime show "Fringe" explores an alternate universe as part of its series-wide plot. The show also touches on crossing over to the other side, the advancement of science and technology bringing two worlds together, as well as the possibility of two worlds colliding and bringing one of them to an end.
Several storylines in the Star Trek and Doctor Who franchises have involved multiverses. Examples include Mirror, Mirror (and sequels) in Star Trek: The Original Series, Parallels in Star Trek: The Next Generation, and Rise of the Cybermen and Turn Left in Doctor Who.
Stargate SG-1 and Stargate Atlantis also have episodes where people travel to different parallel universes.

Other fictional uses

In the card game Magic: The Gathering the different worlds that the characters of the game inhabit, are located throughout what is described as the Multiverse. Certain characters called "Planeswalkers" have the ability to travel to different planes within the Multiverse.
Both DC Comics and Marvel Comics have made extensive use of the multiverse concept, with DC adopting the notion (later adapted by Marvel) of numbering the many different versions of Earth presented, which culminated in the Crisis on Infinite Earths story arc of the 1980s, and its later sequels Infinite Crisis, 52 and Final Crisis. An example of Marvel using the multiverse concept is the Marvel Zombies series which takes place in an alternate universe.
The world of the Chronicles of Chrestomanci ia also a Multiverse.

See also

Notes

  1. ^ James, William, The Will to Believe, 1895; and earlier in 1895, as cited in OED's new 2003 entry for "multiverse": "1895 W. JAMES in Internat. Jrnl. Ethics 6 10 Visible nature is all plasticity and indifference, a multiverse, as one might call it, and not a universe."
  2. ^ Tegmark, Max (May 2003). "Parallel Universes". Scientific American. 
  3. ^ Tegmark, Max (January 23 2003) (PDF). Parallel Universes. http://www.wintersteel.com/files/ShanaArticles/multiverse.pdf. Retrieved 2006-02-07.  (PDF)
  4. ^ a b c d "Parallel universes. Not just a staple of science fiction, other universes are a direct implication of cosmological observations.", Tegmark M., Sci Am. 2003 May;288(5):40-51.
  5. ^ http://arxiv.org/PS_cache/astro-ph/pdf/0302/0302131v1.pdf
  6. ^ Tegmark, Max, The Interpretation of Quantum Mechanics: Many Worlds or Many Words?, 1998. Deutsch, David, David Deutsch's Many Worlds, Frontiers, 1998.
  7. ^ Tegmark, Max (January 23 2003) (PDF). Parallel Universes. http://www.wintersteel.com/files/ShanaArticles/multiverse.pdf. Retrieved 2006-02-07.  (PDF).
  8. ^ J. Schmidhuber (1997): A Computer Scientist's View of Life, the Universe, and Everything. Lecture Notes in Computer Science, pp. 201-208, Springer: IDSIA - Dalle Molle Institute for Artificial Intelligence
  9. ^ J. Schmidhuber (2000): Algorithmic Theories of Everything arXiv.org e-Print archive
  10. ^ J. Schmidhuber (2002): Hierarchies of generalized Kolmogorov complexities and nonenumerable universal measures computable in the limit. International Journal of Foundations of Computer Science 13(4):587-612 IDSIA - Dalle Molle Institute for Artificial Intelligence
  11. ^ J. Schmidhuber (2002): The Speed Prior: A New Simplicity Measure Yielding Near-Optimal Computable Predictions. Proc. 15th Annual Conference on Computational Learning Theory (COLT 2002), Sydney, Australia, Lecture Notes in Artificial Intelligence, pp. 216-228. Springer: IDSIA - Dalle Molle Institute for Artificial Intelligence
  12. ^ Steven Weinberg(2005)"Living in the Multiverse"
  13. ^ a b Richard J Szabo, An introduction to string theory and D-brane dynamics (2004)
  14. ^ a b Maurizio Gasperini, Elements of String Cosmology (2007)
  15. ^ Paul Halpern, The Great Beyond, 2005
  16. ^ Trinh, Xuan Thuan (2006). Staune, Jean. ed. Science & the Search for Meaning: Perspectives from International Scientists. West Conshohocken, PA: Templeton Foundation. p. 186. ISBN 1599471027. 
  17. ^ Baird, Eric (2007). Relativity in Curved Spacetime. Chocolate Tree. p. 241. ISBN 0955706807. 
  18. ^ Lewis, David (1986). On the Plurality of Worlds. Basil Blackwell. 
  19. ^ Deutsch, Harry, "Relative Identity", The Stanford Encyclopedia of Philosophy (Summer '02), Edward N. Zalta (ed.)
  20. ^ Paul B. Kantor "The Interpretation of Cultures and Possible Worlds", 1 October 2002
  21. ^ IngentaConnect Home
  22. ^ The Australian National University
  23. ^ Adi Setia (2004), "Fakhr Al-Din Al-Razi on Physics and the Nature of the Physical World: A Preliminary Survey", Islam & Science 2, http://findarticles.com/p/articles/mi_m0QYQ/is_2_2/ai_n9532826/, retrieved 2010-03-02 
  24. ^ Carl Sagan, Placido P D'Souza (1980s). 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 – from the Babylonians to the Maya.
  25. ^ "John Grant" interviewed by Lou Anders, accessed 24 October 2009
  26. ^ [Robert A. Heinlein: A Reader's Companion, James Gifford, Nitrosyncretic Press, Sacramento, California, 2000.]

References

  • Bernard Carr, ed. (2007) Universe or Multiverse? Cambridge Univ. Press.
  • Deutsch, David (45841 1985). Splash. ed. Quantum theory, the Church-Turing principle and the universal quantum computer (Proceedings of the Royal Society of London A 400 ed.). pp. 97–117. 

External links


Simple English

A multiverse (or meta-universe) is the theory of a set of multiple possible universes, including our universe, which make up reality. These universes are sometimes called parallel universes. It is believed by some[who?] physicists that our universe is perfect for life, because it had thousands of other chances at life, each of which is a different universe in the multiverse. The term "multiverse" was coined by psychologist William James.[1]

References

  1. James, William, The Will to Believe, 1895; and earlier in 1895, as cited in OED's new 2003 entry for "multiverse": "1895 W. JAMES in Internat. Jrnl. Ethics 6 10 Visible nature is all plasticity and indifference, a multiverse, as one might call it, and not a universe."

Citable sentences

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