Physical cosmology

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The multiverse (or meta-universe) is the hypothetical set of multiple possible universes (including our universe) that together comprise all of reality. Physical cosmology, as a branch of Astronomy, is the study of the large-scale structure of the Universe and is concerned with fundamental questions about its The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. The age of the Universe is the time elapsed between the theory of the Big Bang and the present day This timeline of the Big Bang describes the events according to the Scientific theory of the Big Bang, using the cosmological time parameter of Comoving coordinates The ultimate fate of the universe is a topic in Physical cosmology. The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy Reality, in everyday usage means "the state of things as they actually exist" The different universes within the multiverse are sometimes called parallel universes or dimensions. 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, theology, and fiction, particularly in science fiction and fantasy. Cosmology (from Greek grc κοσμολογία - grc κόσμος kosmos, "universe" and grc -λογία -logia) is study Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study Philosophy is the study of general problems concerning matters such as existence knowledge truth beauty justice validity mind and language Theology is the study of a god or the gods from a religious perspective Fiction is the telling of stories which are not real More specifically fiction is an imaginative form of Narrative, one of the four basic Rhetorical modes. Fantasy is a Genre that uses magic and other Supernatural forms as a primary element of plot, theme, and/or setting The specific term "multiverse," which was coined in 1895 by psychologist William James,^[1] was popularized by science fiction author Michael Moorcock. For other people named William James see William James (disambiguation William James (January 11 1842 – August 26 1910 was a pioneering Michael John Moorcock (born 18 December 1939, in London) is an English writer primarily of Science fiction and fantasy who has also In these contexts, parallel universes are also called "alternative universes," "quantum universes," "parallel worlds," "alternate realities," "alternative timelines," etc.

Multiverse hypotheses in physics

Laura Mersini-Houghton claims that the WMAP cold spot may provide testable empirical evidence for a parallel universe within the multiverse. Dr Laura Mersini-Houghton (née Laura Mersini is a theoretical Physicist - Cosmologist and professor at the University of North Carolina at Chapel Hill In 2004 the Wilkinson Microwave Anisotropy Probe (WMAP mapped out a region in the Eridanus Constellation which had Cosmic microwave background radiation (CMB that According to Max Tegmark,^[2] the existence of other universes is a direct implication of cosmological observations. Max Tegmark (born 5 May 1967) is a Swedish - American cosmologist. 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]

Classification

In order to clarify terminology, George Ellis, U. George F R Ellis, FRS, (born August 11, 1939) is the Distinguished Professor of Complex Systems in the Department of Mathematics and Applied 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. Topology ( Greek topos, "place" and logos, "study" is the branch of Mathematics that studies the properties of SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS The Chaotic Inflation theory is a variety of the Inflationary universe model which is itself an outgrowth (or extension of the Big bang theory ^[4]

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

Multi-domain universes (Ellis, Kirchner 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. In Physical cosmology, cosmic inflation is the idea that the nascent Universe passed through a phase of exponential expansion that Infinity (symbolically represented with ∞) comes from the Latin infinitas or "unboundedness In Physics and Thermodynamics, the ergodic hypothesis says that over long periods of time the time spent by a particle in some region of the Phase space The Hubble volume, or Hubble sphere, is the volume of the Universe bounded by the Hubble limit.

Universes with different physical constants

Level II: (Andrei Linde's bubble theory) In chaotic inflation, other thermalized regions may have different effective physical constants, dimensionality and particle content. Andrei Dmitriyevich Linde (b March 2, 1948 in Moscow, USSR) is a Russian-American theoretical Physicist and Professor The Chaotic Inflation theory is a variety of the Inflationary universe model which is itself an outgrowth (or extension of the Big bang theory The Chaotic Inflation theory is a variety of the Inflationary universe model which is itself an outgrowth (or extension of the Big bang theory A physical Constant is a Physical quantity that is generally believed to be both universal in nature and constant in time (Surprisingly, this level includes Wheeler's oscillating universe theory as well. The oscillatory universe is a Cosmological model, originally derived by Alexander Friedman in 1922 investigated briefly by Einstein in 1930 and critiqued )

Multiverses (Ellis, Kirchner 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. Hugh Everett III ( November 11, 1930 – July 19, 1982) was an American physicist who first proposed the Many-worlds interpretation The many-worlds interpretation or MWI (also known as relative state formulation, theory of the universal wavefunction, parallel universes, Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons 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. In Mathematical logic, a Logical theory T_2 is a ( proof theoretic) conservative extension of a theory T_1 if the language of T_2 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. David Elieser Deutsch FRS (born 1953 in Haifa, Israel) is a Physicist at the University of Oxford. ^{[5] [6]}

Ultimate ensemble

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. Since this subsumes all other possible ensembles, it brings closure to the hierarchy of multiverses: there cannot be a Level V.

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. Jürgen Schmidhuber (born 1963 in Munich) is a Computer scientist and Artist known for his work on Machine learning, universal In the fields of Architecture and Civil engineering, construction is a process that consists of the Building or assembling of Infrastructure Computer programs (also software programs, or just programs) are instructions for a Computer. 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 ^[7][8][9]. Kurt Gödel (kʊɐ̯t ˈgøːdl̩ (April 28 1906 – January 14 1978 was an Austrian American Logician, Mathematician and Philosopher He also explicitly discusses the more restricted ensemble of quickly computable universes ^[10].

Bubble theory

"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.

Bubble theory posits an infinite number of open multiverses, each with different physical constants. A physical Constant is a Physical quantity that is generally believed to be both universal in nature and constant in time (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. Andrei Dmitriyevich Linde (b March 2, 1948 in Moscow, USSR) is a Russian-American theoretical Physicist and Professor This Bubble universe theory fits well with the widely accepted theory of cosmic inflation. The Chaotic Inflation theory is a variety of the Inflationary universe model which is itself an outgrowth (or extension of the Big bang theory In Physical cosmology, cosmic inflation is the idea that the nascent Universe passed through a phase of exponential expansion that The bubble universe concept involves creation of universes from the quantum foam of a "parent universe. Quantum foam, also referred to as spacetime foam, is a concept in Quantum mechanics, devised by John Wheeler in 1955. " On very small scales, the foam is frothing due to energy fluctuations. These fluctuations may create tiny bubbles and wormholes. In Physics, a wormhole is a hypothetical topological feature of Spacetime that is fundamentally a 'shortcut' through Space and Time 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.

Many worlds interpretation of quantum physics

Hugh Everett's many-worlds interpretation (MWI) is one of several mainstream interpretations of quantum mechanics. Hugh Everett III ( November 11, 1930 – July 19, 1982) was an American physicist who first proposed the Many-worlds interpretation The many-worlds interpretation or MWI (also known as relative state formulation, theory of the universal wavefunction, parallel universes, An interpretation of quantum mechanics is a statement which attempts to explain how Quantum mechanics informs our Understanding of Nature. Other interpretations include the Copenhagen and the consistent histories interpretations. The Copenhagen interpretation is an interpretation of Quantum mechanics. In Quantum mechanics, the consistent histories approach is intended to give a modern Interpretation of quantum mechanics, generalising the conventional Copenhagen 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^[11] through quantum interference. In physics interference is the addition ( superposition) of two or more Waves that result in a new wave pattern ^[12] 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. Quantum superposition is the fundamental law of Quantum mechanics. The Universal Wavefunction or Universal Wave Function is a term introduced by Hugh Everett in his Princeton PhD Thesis entitled The Theory of the Universal Wave Related are Richard Feynman's multiple histories interpretation and H. Dieter Zeh's many-minds interpretation. Richard Phillips Feynman (ˈfaɪnmən May 11 1918 – February 15 1988 was an American Physicist known for the Path integral formulation of quantum The concept of multiple histories is closely related to the Many-worlds interpretation of Quantum mechanics. Heinz-Dieter Zeh (usually referred to as H Dieter Zeh) (born 8 May 1932) is a Professor Emeritus of the University of Heidelberg The many-minds interpretation of Quantum mechanics extends the Many-worlds interpretation by proposing that the distinction between worlds should be made at the level

Many worlds interpretation cannot explain the apparently Fine-tuned universe. The fine-tuned Universe is the idea that the conditions that allow Life in the Universe can only occur when certain universal Physical constants lie within 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. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 See Rare Earth hypothesis. In Planetary astronomy and Astrobiology, the Rare Earth hypothesis argues that the emergence of complex Multicellular life ( Metazoa 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. String theory is a still-developing scientific approach to Theoretical physics, whose original building blocks are one-dimensional extended objects called strings In Theoretical physics, M-theory is a new limit of String theory in which 11 dimensions of Spacetime may be identified In M-theory our universe and others are created by collisions between membranes in an 11-dimensional space. This is unlike the universes in the "quantum multiverse". The many-worlds interpretation or MWI (also known as relative state formulation, theory of the universal wavefunction, parallel universes,

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. The string theory landscape or anthropic landscape refers to the large number of possible false vacua in String theory.

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. In Philosophy, empiricism is a theory of Knowledge which asserts that knowledge arises from Experience. Testability, a property applying to an Empirical Hypothesis, involves two components (1 the logical property that is variously described as Contingency Falsifiability (or "refutability" is the logical possibility that an assertion can be shown false by an observation or a physical experiment Scientific method refers to bodies of Techniques for investigating phenomena

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. Leonard Susskind (born 1940 is the Felix Bloch professor of Theoretical physics at Stanford University in the field of String theory and

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. Occam's razor (sometimes spelled Ockham's razor) is a principle attributed to the 14th-century English Logician and Franciscan Friar,

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, wave function collapse and ontological asymmetry. In Mathematics, a finite topological space is a Topological space for which the underlying point set is finite. In certain interpretations of quantum mechanics, wave function collapse is one of two processes by which Quantum systems apparently evolve according to the laws of Our judgment therefore comes down to which we find more wasteful and inelegant: many worlds or many words. "^[13] Thus, according to Tegmark, paradoxically the multiverse scenario is more parsimonious than that of a single universe. This reflects an old insight from algorithmic information theory: the information conveyed by a set may be far less than the information conveyed by its individual elements. Algorithmic information theory is a subfield of Information theory and Computer science that concerns itself with the relationship between computation According to Jürgen Schmidhuber, the appropriate mathematical theory of Occam's razor already exists, namely, Ray Solomonoff's theory of optimal inductive inference ^[14] and its extensions ^[15]. Jürgen Schmidhuber (born 1963 in Munich) is a Computer scientist and Artist known for his work on Machine learning, universal Occam's razor (sometimes spelled Ockham's razor) is a principle attributed to the 14th-century English Logician and Franciscan Friar, Ray Solomonoff (born 1926 Cleveland Ohio son of Russianimmigrants invented Algorithmic Probability in 1960

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

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. Einstein raised this possibility when he wondered whether the universe could have been otherwise, or non-existent altogether. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical This possibility is also expressed in theories such as determinism and chaos theory. Determinism is the philosophical Proposition that every event including human cognition and behaviour decision and action is causally determined In Mathematics, chaos theory describes the behavior of certain dynamical systems – that is systems whose state evolves with time – that may exhibit dynamics that 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. A theory of everything ( TOE) is a putative Theory of Theoretical physics that fully explains and links together all known physical phenomena

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. Intelligent William Dembski in particular, derides it as inflating explanatory resources without evidence or warrant, and terms such concepts "inflatons". William Albert "Bill" Dembski (born July 18 1960) is an American proponent of Intelligent design, and its opposition to the The inflaton is the generic name of the unidentified scalar field (and its associated particle that may be responsible for an episode of inflation in the very early ^[16]

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. In Physics and Cosmology, the anthropic principle states that humans should take into account the constraints that human existence imposes on the kind of theoretical The fine-tuned Universe is the idea that the conditions that allow Life in the Universe can only occur when certain universal Physical constants lie within 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. Life is a state that distinguishes Organisms from non-living objects such as non-life and dead organisms being manifested by growth through Metabolism 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. A teleological argument, or argument from design, is an Argument for the Existence of God or a creator based on perceived evidence of order purpose design

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. Stephen Jay Gould (September 10 1941 &ndash May 20 2002 was a prominent American paleontologist, evolutionary biologist, and historian of science Clinton Richard Dawkins, FRS, FRSL (born 26 March 1941 is a British ethologist, evolutionary biologist, and Popular science Dr. Gould compared it to claiming that sausages were originally made long and narrow so that they would fit modern hotdog buns, or that humans evolved fingernails so that fingernail polish would 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). David Kellogg Lewis ( September 28, 1941  &ndash October 14, 2001) is considered to have been one of the leading philosophers of the latter Modal realism is the view notably propounded by David Lewis, that Possible worlds are as real as the actual world ^[17]

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. Counterpart theory ( CT) is a theoretical framework It uses the counterpart relation (hereafter C-relation to replace the identity relation between objects in different David Lewis may refer to: Academics David Lewis (lawyer (c1520–1584 civil lawyer and first Principal of Jesus College Oxford David ^[18][19]

Virtual realities as a multiverse

Further information: Simulated reality

Some scientists entertain the possibility of creating artificial conscious machines, and some artificial intelligence advocates even claim we are not far from producing conscious computers. Simulated reality is the proposition that Reality could be simulated—perhaps by Computer simulation —to a degree indistinguishable from "true" Reality It is then but a small step to the point where the engineered conscious beings inhabit a simulated reality. Simulated reality is the proposition that Reality could be simulated—perhaps by Computer simulation —to a degree indistinguishable from "true" Reality For such beings, their "fake" universe will appear indistinguishable from reality.

Multiverse hypotheses in religions around the globe

Hindu universes

The earliest known records describing the concept of a multiverse are found in ancient Hindu cosmology, in texts such as the Puranas. According to Hindu mythology and Cosmology, the universe is cyclically created and destroyed For other meanings see Purana (disambiguation. The Puranas ( Sanskrit: sa पुराण purāṇa, "of ancient times" 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 is infinite. ^[20]

Fictional multiverses

The concept of the multiverse has been used in fiction and information on this can be found in the following article: Parallel universe (fiction). Parallel universe or alternative reality is a self-contained separate reality coexisting with one's own

See also

• The Fabric of Reality
• Fictional universe
• Multiple histories
• Parallel universes in fiction
• Philosophy of physics
• Philosophy of space and time
• Planescape
• Quantum gravity
• Reductionism
• Simulated reality
• String theory landscape
• Counterpart theory

Notes

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.  

External links

• Physics in the Multiverse, published by Aurélien Barrau in the CERN Courier
• Preprint of David Deutsch's paper The Structure of the Multiverse
• BBC Horizon -Parallel Universes
• Michael Price's Everett FAQ
• Mulitverse Cosmological Models by P. Aurélien Barrau is a French Astrophysicist, specialized in Astroparticle physics, Black holes and cosmology. C. W. Davies
• The ensemble of universes describable by constructive mathematics by Jürgen Schmidhuber
• 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.
• Joseph Pine II about Multiverse, Presentation at Mobile Monday Amsterdam, 2008