Multiverse

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Although no scientific evidence suggesting the possibility of other realms outside our own universe has been discovered yet, the concept of other universes (also described as "alternate" universes) has been proposed by theoretical scientists. In the absence of direct evidence, the case for multiple universes is related to the principle of Ockham's Razor; the existence of our universe and possibly quantum decoherence within it are most simply explained by the existence of many universes. Further the apparent fine tuning of the universe can be explained by the multiverse theory.

There is also a strong line of reasoning leading to the conclusion that all possible worlds exist.

A majority of cosmologists now believe that Everett's many-worlds interpretation of quantum theory is correct. (Source: Michael Price's Everett FAQ)

The Multiverse is a concept derived originally, by philosophers in prior centuries; but theoretical physicist David Deutsch was the first to discover and contribute physical evidence to support the theory on a quantum scale. David Deutsch is also a major proponent of the collaboration of scientists working to instill factuality of quantum theory on a macrocosmic level. Deutsch specializes in quantum computing, a modern revolution in computer technology.

The term was invented in December 1960, by Andy Nimmo, then vice chairman of the British Interplanetary Society, Scottish Branch, for a talk on the Everett many-worlds interpretation of quantum physics which had been published in 1957, to the branch. This was given in February 1961, and the word with its original definition, "an apparent universe, a multiplicity of which, go to make up the whole universe" was then first used. This was because the then dictionary definition of the word 'universe' was, "All that there is" and one cannot have "Alls that there is" etymologically. 'Uni' means one, and 'multi' means many, so you can have many multiverses.

The concept of the Multiverse is present in the recent box-office hit, "The One", starring Jet Li.

The Multiverse was physically conveyed through the product of the famous "double-slit experiment" (invented by Thomas Young in 1803 - long before quantum theory) in which photons were emitted at a wall with 2 openings, and the sensor behind the wall recorded the collision points of the photons. As one photon was emitted, multiple points were registered on the grid, thus conveying the idea that the photon (a quanta of light) was making multiple decisions. The data is also recorded with sensitive "quantum" cameras.

Template:Cosmology A multiverse (or meta-universe) is the hypothetical set of multiple possible universes (including our universe) that together comprise all of physical reality. The different universes within a 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, philosophy, theology, and fiction, particularly in science fiction and fantasy. The specific term "multiverse," which was coined by William James,^[1] was popularized by science fiction author Michael Moorcock. In these contexts, parallel universes are also called "alternative universes," "quantum universes," "parallel worlds," "alternate realities," "alternative timelines," etc.

The possibility of many universes raises various scientific, philosophical, and theological questions.

Multiverse hypotheses in physics

Classification

According to Max Tegmark,^[2] 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.^[3] 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 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.^[4]

The levels according to Tegmark's classification and using Ellis, Koechner and Stoeger's terminology are briefly described below.

Multi-domain universes (Ellis, Koechner and Stoeger sense):

Level I: (Open multiverse) A generic prediction of cosmic inflation is an infinite ergodic universe, which, being infinite, must contain Hubble volumes realizing all initial conditions – including an identical copy of a given person about <math>10^{10^{29}}</math> m away.[1] See also Criticism of Many worlds in one

Level II: (Andrei Linde's bubble theory) In chaotic inflation, other thermalized regions may have different effective physical constants, dimensionality and particle content. (Surprisingly, this level includes Wheeler's oscillating universe theory as well.)

Multiverses (Ellis, Koechner and Stoeger sense)

Level III: (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".

Level IV: (The ultimate "Ensemble theory" of Tegmark) Other mathematical structures give different fundamental equations of physics. This level considers "real" any hypothetical universe based on one of these structures. M-theory might be placed here. Since this subsumes all other possible ensembles, it brings closure to the hierarchy of multiverses: there cannot be a Level V. The question is open whether or not scientists will subdivide Level IV in the future.

Open multiverse

Some physicists believe that the universe is spatially unbounded. The theory of relativity places a firm upper limit on the speed at which information can travel. Nothing except hypothetically Tachyons can travel faster than light. This effectively divides this infinite space into "local" universes. Our observable universe, for example, is a sphere centered on the Earth (centered, that is, on whoever is doing the calculating), currently about 46.5 billion light years in radius.

Thus, there are an infinite number of regions of space the same size as our observable universe – an infinite number of observable universes, that is. This infinite set (which must contain, among other things, an infinite number of identical copies of you,^[5] the nearest of which is about <math>10^{10^{29}}</math> m away, and an equally infinite number of not-quite-identical copies) comprises the level-I multiverse. By the Bekenstein bound there are only a finite number of configurations possible within any region, hence exact duplication is inevitable.

Overtly or not, physicists often use the idea of an Open Multiverse when evaluating theories. For example, Max Tegmark writes:

...consider how cosmologists used the microwave background to rule out a finite spherical geometry. Hot and cold spots in microwave background maps have a characteristic size that depends on the curvature of space, and the observed spots appear too small to be consistent with a spherical shape. But it is important to be statistically rigorous. The average spot size varies randomly from one Hubble volume to another, so it is possible that our universe is fooling us – it could be spherical but happen to have abnormally small spots. When cosmologists say they have ruled out the spherical model with 99.9 percent confidence, they really mean that if this model were true, fewer than one in 1,000 Hubble volumes would show spots as small as those we observe.

Bubble theory

Bubble theory posits an infinite number of open multiverses, each with different physical constants. (The set of bubble universes is thus a Level II multiverse.) Counter-intuitively, these universes are farther away than even the farthest universe in our open multiverse.

The formation of our universe from a "bubble" of a multiverse was proposed by Andre Linde. This Bubble universe theory fits well with the widely accepted theory of cosmic inflation. The bubble universe concept involves creation of universes from the quantum foam of a "parent universe." On very small scales, the foam is frothing due to energy fluctuations. These fluctuations may create tiny bubbles and wormholes. If the energy fluctuation is not very large, a tiny bubble universe may form, experience some expansion like an inflating balloon, and then contract and disappear from existence. However, if the energy fluctuation is greater than a particular critical value, a tiny bubble universe forms from the parent universe, experiences long-term expansion, and allows matter and large-scale galactic structures to form.

Big bounce

According to some quantum loop gravity theorists, the Big Bang was merely the beginning of a period of expansion that followed a period of contraction. In this oscillatory universe hypothesis (originally attributable to John Wheeler), the universe undergoes an infinite series of oscillations, each beginning with a big bang and ending with a big crunch. After the big bang, the universe expands for a while before the gravitational attraction of matter causes it to collapse back in and undergo a Big bounce. Although the model was abandoned for a time, the theory has been revived in brane cosmology as the cyclic model.

Like Bubble Theory, this oscillatory view posits a Level-II multiverse.

Many worlds interpretation of quantum physics

Hugh Everett's many-worlds interpretation (MWI) is one of several mainstream interpretations of quantum mechanics. Other interpretations include the 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^[6] through quantum interference.^[7] 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.

M-theory

A multiverse of a somewhat different kind has been envisaged within the 11-dimensional extension of string theory known as M-theory. In M-theory our universe and others are created by collisions between membranes in an 11-dimensional space. Unlike the universes in the "quantum multiverse", these universes can have different laws of physics.

String landscape

The string landscape theory asserts that a different universe exists for each of the very large ensemble of solutions generated when ten dimensional string theory is reduced to the four-dimensional low-energy world we see.

Criticisms of multiverse theories

Non-scientific claims

Critics claim that these theories lack empirical correlation and testability, and without hard physical evidence are unfalsifiable; outside the methodology of scientific investigation to confirm or disprove; and therefore more mathematically theoretical and metaphysical than scientific in nature.

Tegmark notes that improved measurements of the microwave background radiation and of the large-scale distribution of matter may fortify or knock down two pillars of the multiverse – the infinitude of space and the theory of chaotic inflation – so at least part of the theory may be testable. However, chaotic inflation is not the only version of cosmic inflation that can lead naturally to the multiverse hypothesis, as "new inflation" is also eternal and offers a scientific justification of the anthropic principle. Furthermore, not all models of inflation are eternal.

Bad science

Some have argued that the job of a scientist is to provide fundamental explanations for observed phenomena, without making reference to observers. Resorting to anthropic principles constitutes a "lazy way out" of accounting for features such as the apparent fine-tuning of parameters in relation to the existence of life.

Leonard Susskind claims, however, that some form of multiverse is unavoidable, given the current state of physics, and that observer effects are inevitable and have to be taken into account in other sciences.

Occam's Razor

To postulate an infinity of unseen and unseeable verses 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 verses by default. To deny the existence of those verses, 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."^[8] Thus, according to Tegmark, paradoxically the multiverse scenario is more parsimonious than that of a single verse.

David Lewis, however, draws a distinction between qualitative and quantitative excess. Postulating extra universe just like our own does not increase the number of kinds of things there are, and thus is only quantitative excess.

One unique universe

It is sometimes argued that the observed universe is the unique possible universe, so that talk of "other" universes is ipso facto meaningless. The above fails to state why the observed universe is unique. Einstein raised this possibility when he wondered whether the universe could have been otherwise, or non-existent altogether. This possibility is also expressed in theories such as determinism and chaos theory. The hope is sometimes expressed that once a grand unified theory of everything is achieved, it will turn out to have a unique "solution" corresponding to the observed universe.

Creating more problems

Multiverse proponents are often vague about how the parameter values are selected across the defined ensemble. If there is a "law of laws" or meta-law describing how parameter values are assigned from one universe to the next, then we have only shifted the central problems of cosmology up one level, because we need to explain where the meta-law comes from. Moreover, the set of such meta-laws is infinite, so we have merely replaced the question "why this universe?" with "why this meta-law?". There would seem to be little point in invoking an infinite number of universes when it would be simpler to postulate a single universe with a single principle. There is no reason to assume that any meta-law is fine-tuned. We do not know whether or not any meta-law would have to be in a narrow range to allow at least one universe like ours. We do not know enough about any meta-law to say whether it needs to be fine-tuned or can be coarsely-tuned.

Tegmark maintains that in his extreme multiverse theory this problem is circumvented, because in that case all possible meta-laws (or all possible unified theories) are in force and describe really-existing multiverses. However, his ultimate ensemble is still restricted to mathematical (or mathematically describable) laws, processes and structures. If it is in any way possible for something non-mathematical to exist, his ensemble is not ultimate, and relies on a contingent meta-law law excluding the non-mathematical from actual existence.

Other objections

Another objection to the existing multiverse theories is a challenge to the criteria for defining universes. In most multiverse theories, universes are labeled by laws of physics and initial conditions. It might be argued that these terms are narrow and chauvinistic; there may be criteria for categorization that lie completely beyond the scope of human comprehension.

However, any algorithmic form is covered by Max Tegmark's ultimate ensemble.

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 "inflatons".^[9]

Anthropic principle

Main article: 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 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 multiverses, this scarcity of life-supporting universes does not imply intelligent design as the only explanation of our existence.

Critics of this argument (Steven Jay Gould, Richard Dawkins and many others) point out that the cause and the effect have been reversed by those who claim that the universe seems to be fine-tuned for our benefit. Dr. Gould compared it to claiming that hotdogs were originally made long and narrow so that they would fit modern hotdog buns, or that humans evolved fingernails because fingernail polish would inevitably be invented. Critics cite the vast store of evolutionary evidence which shows that life is perfectly and naturally tuned to the universe it arose in. Fossil, genetic and other biological evidence abundantly supports the observation that life adapts to physics, not the other way around.

The paleophysicist Caroline Miller writes: "The Anthropic Principle is based on the underlying belief that the universe was created for our benefit. Unfortunately for its adherents, all of the reality-based evidence at our disposal contradicts this belief. In a non-anthropocentric universe, there is no need for multiple universes or supernatural entities to explain life as we know it."

Modal realism

Additionally, 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).^[10]

Trans-world identity issues

A metaphysical issue that crops up with 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. David Lewis then proposed his counterpart theory where he substitutes the identity relation between possible worlds for a similarity relation.

The problem

The problem lies in the tension between classical notions of identity and quantum indeterminacy. In short, quantum reality does not allow classical – radically mechanical – 'identities' due to the Heisenberg Uncertainty Principle. However, in an infinite set of possible universes such a correspondence is presumed to exist. The question then becomes whether one can claim a distinction between entities that vary only in terms of some arbitrary dimensional metric in De Sitter space.

Suggested resolutions include the possibilities that:

• Synchronous unitemporal parallel universe ontologies are invalid.
• Synchronous unitemporal parallel universes belong to a part-whole relationship.
• Quantum fluctuations average out within the Heisenberg limit between duplicates.
• Alternative criteria are needed to hermeneutically assess the concept of 'identity'.
• Objects may not be completely identical. Nonquantifiable attributes of objects may vary over an infinite range.
  See, Criticism of Many worlds in one

Relative Identity

Trans-world identity is also considered in depth in possible worlds concepts.^[11][12]

Virtual realities as a multiverse

Further information: Simulated reality

Most scientists are prepared to entertain the possibility of conscious machines, and some artificial intelligence advocates even claim we are not far from producing conscious computers. It is then but a small step to the point where the engineered conscious beings inhabit a simulated reality. For such beings, their "fake" universe will appear indistinguishable from reality. So should we include these simulated universes in the ensemble that constitutes the multiverse? Is it meaningful to assign equal ontological status to our own, observed, universe and universes that are virtual? If it is not then is it meaningful to assign equal ontological status to our own, observed, universe and universes that can never be observed by any sentient being?

Incidentally, this of course assumes that our observed universe is 'real' and not virtual; at least one philosopher, Nick Bostrom, has proposed that this may not be the case.

Multiverse hypotheses in philosophy

Sikh beliefs

Sikh believe in the multiverse, and in relativity. In Japji Sahib, Stanza 22, it is written: patala patal lakh agasa agas ("there are countless world beneath us and countless world above us"; ਖੰਡ ਪਤਾਲ ਅਸੰਖ ਮੈ ਗਣਤ ਨ ਹੋਈ ॥ "There are countless worlds and nether regions; I cannot calculate their number"; see Guru Granth Sahib.)

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.^[13]

Other contemporary religious references

Main article: Mormon cosmology

The Church of Jesus Christ of Latter Day Saints (the "Mormon Church") has a concept which dovetails somewhat with theories of multiple universes, though there is no church position on this.

Fictional multiverses

Main article: Parallel universe (fiction)

The word was then both used correctly and misused in both scientific and science fiction circles over several years by those who attended the meeting and others. In the late 1960s science fiction author Michael Moorcock interpreted the word in a novel that was read by David Deutsch. Deutsch then used the term "multiverse" in a scientific work as the totality of all possible universes throughout time, including our observable universe- the opposite of its previous definition. Other scientists, not being etymologists, then picked up and adopted the popular redefinition of the word. The popular comic book publishers Marvel Comics and DC Comics each have their own fictional "multiverses" that exist within the framework of their separate continuities.

A large number of fantasy stories involve a character being suddenly transported from one world or universe (often from our own Earth) into another universe. Notable stories of this sort include the Thomas Covenant stories of Stephen R. Donaldson, and the Guardians of the Flame series by Joel Rosenberg.

Michael Crichton, the author of 'Jurassic Park' also delved into the possibility of travel between other realities in the multiverse in his novel Timeline.

The concept of the multiverse figures prominently in many science fiction and fantasy novels. Among the more famous fictional "multiverses" are those of Michael Moorcock, though "alternate universe" stories have appeared in popular science fiction. A classic episode of Star Trek entitled "Mirror, Mirror" featured an "alternate" version of the Star Trek universe where the main characters were barbaric and evil. The science fiction TV series Sliders is founded upon the idea of an infinite number of "alternate" Earths, with each Earth existing in a different and separate universe.

On developing his concept of the multiverse, Moorcock was developing his "Eternal Champion" stories at around the time Everett was developing his theory. Moorcock first used the term in print in the 1962 novel The Blood-Red Game. In the same year, the original Eternal Champion novella was published in Science Fantasy Magazine. On the influence of Everett's work, he says:

It was an idea in the air, as most of these are, and I would have come across a reference to it in New Scientist (one of my best friends was then editor) ... [or] physicist friends would have been talking about it. ... Sometimes what happens is that you are imagining these things in the context of fiction while the physicists and mathematicians are imagining them in terms of science. I suspect it is the romantic imagination working, as it often does, perfectly efficiently in both the arts and the sciences.

The concept of the multiverse figures prominently in many science fiction and fantasy novels. For some it serves primarily as a plot device, a means to put characters into an unfamiliar situation, or a framework that usually lies in the background for continuity purposes. For others it is a major theme and focus of the work. It is sometimes used as the basis for exploring "what if" scenarios, such as in alternate history stories. The film The One (2002) starring Jet Li carried the same idea to the action film medium. The popular MYST computer game franchise uses concepts of describing a world and then linking to that world, which is part of a multiverse of infinite possible and concurrently existing universes, matching the descriptions. Also, the computer game Legacy of Kain: Soul Reaver and its sequels feature two distinct parallel universes. The protagonist, Raziel, is capable of existing in both the Material Realm, or normal reality, and the Spectral Realm, a dark and distorted version of the former with its own physics and properties. The Michael Crichton novel Timeline featured a method for what appeared to be time travel by traveling to parallel universes that are identical except for the moment of their birth, thus rendering off-set yet parallel time. The DC Universe, famous home of Batman and Superman, uses the multiverse as the basis for their universe. This is in part to help deal with their 67 year history. In the 1980s DC published the ever popular Crisis on Infinite Earths which detailed a breakdown of the Multiverse at the hands of the Anti-Monitor. The television series Star Trek has many times gone into parallel "Mirror" universes, and Stargate SG-1 has postulated parallel universes. The Anime series Bokurano is based on a multiverse.

References

• Deutsch, David (45841 1985). in Splash: Quantum theory, the Church-Turing principle and the universal quantum computer, Proceedings of the Royal Society of London A 400, mos craciun, 97-117. iulianveza12@yahoo.com. 

See also

• The Fabric of Reality
• Fictional universe
• Multiple histories
• Parallel universe
• Philosophy of physics
• Philosophy of space and time
• Quantum gravity
• Reductionism
• Simulated reality
• String theory landscape
• His Dark Materials
• Counterpart theory

External links

• Preprint of David Deutsch's paper The Structure of the Multiverse
  • http://xxx.lanl.gov/abs/quant-ph/0104033
• The relevant part of Michael Price's Everett FAQ
  • http://www.hedweb.com/manworld.htm#believes
• Preprint of David Deutsch's paper The Structure of the Multiverse
• BBC Horizon -Parallel Universes
• Michael Price's Everett FAQ
• Against Many-Worlds Interpretations Adrian Kent, The Institute for Advanced Study, School of Natural Sciences, Princeton, New Jersey
• 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
• Mulitverse Cosmological Models by P.C.W. Davies
• The 'Everything' mailing list (and archives), A "discussion of the idea that all possible universes exist".
• 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 ThoughtCast.

References

• Adapted from the Wikipedia article, "Multiverse" http://en.wikipedia.org/wiki/Multiverse, used under the GNU Free Documentation License