 | Multiverse: Encyclopedia II - Multiverse - Multiverse hypotheses in physics
Multiverse - Multiverse hypotheses in physics
Multiverse - Classification
According to Max Tegmark, the existence of other universes are a direct implication of cosmological observations. In an article entitled "Parallel Universes" in the May 2003 issue of Scientific American, he presents a clear and comprehensive picture of the idea of parallel universes. Tegmark describes the set of related concepts which share the notion that there are universes beyond the familiar observable one. He goes on to provide a taxonomy of parallel universes organized by levels.
Level I: (Open multiverse) A generic prediction of cosmic inflation is an infinite ergodic universe, which contains Hubble volumes realizing all initial conditions - including an identical copy of you about meters away.
Level II: (Andre 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.
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 is concerned, it leads to no new results. According to Tegmark "This 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. M-theory would be placed here. Since this subsumes all other ensembles, it therefore brings closure to the hierarchy of multiverses: there cannot be a Level V.
Multiverse - Open multiverse
Alexander Vilenkin, with Jaume Garriga and others, have recently argued that there are an infinite number of regions of space the same size as our observable universe that is, that one can travel forever in any direction and always continue to reach new points. This assumption relies on the theory that at some stage in the past matter was distributed fairly evenly across space, and later condensed to form objects dense enough to become the source for a big bang. However, in this situation we would expect that rather than there being only a single big bang, matter would condense in a number of places separated by astronomical distances, forming a network or lattice of big bangs all exploding and then contracting like a network of flashing lights or the atoms in a crystal. Thus, rather than having a single big bang and a single universe, there would be a collection of universes, or a multiverse.
Multiverse - Bubble Theory
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 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.
Multiverse - 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.
Multiverse - Many world 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. The state of the entire multiverse is related to the states of the constituent universes by quantum superposition. Related are Richard Feynman's multiple histories interpretation and H. Dieter Zeh's many-minds interpretation.
Multiverse - 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 completely different laws of physics—anything may be possible.
Multiverse - String Landscape
Another proposal for a multiverse in string theory, this type IIB string theory, has received considerable attention lately. It is called the string landscape and asserts that, roughly speaking, there are a very large number of ways to go from ten dimensional string theory down to the four-dimensional low-energy world we see, and each one of these corresponds to a radically different universe.
Other related archivesAge of the universe, Alexander Vilenkin, Andre Linde, Anthropic Principle, Anthropic landscape, Astrophysics, Big Bang, Big bounce, Bubble universe theory, Catholic Church, Christoph Schönborn, Comoving distance, Copenhagen, Cosmic microwave background, Dark energy, Dark matter, David Lewis, De Sitter space, Einstein, FLRW metric, Fine-tuned universe, Friedmann equations, Galaxy formation, General relativity, H. Dieter Zeh, Heisenberg limit, Hubble's law, Hugh Everett, Inflation, John Wheeler, Lambda-CDM model, Large-scale structure, Leonard Susskind, M-theory, Max Tegmark, Modal realism, Nucleosynthesis, Observable universe, Occam's Razor, Parallel universe, Particle physics, Philosophy of physics, Philosophy of space and time, Possible worlds, Quantum fluctuations, Quantum gravity, Redshift, Reductionism, Richard Feynman, Scientific American, Shape of the universe, Theory of relativity, Timeline of cosmology, Timeline of the Big Bang, Ultimate fate of the universe, Uncertainty Principle, Universe, William Dembski, alternative history (fiction), anthropic principle, artificial intelligence, astronomical distances, atoms, big bang, big crunch, biology, brane cosmology, chaotic inflation, conscious computers, conservative extension, consistent histories, cosmic inflation, crystal, cyclic model, design, empirical, ergodic, fine-tuned, fine-tuning, hermeneutically, identity, infinite, inflatons, initial conditions, intelligent design, interpretations of quantum mechanics, life, many-minds interpretation, many-worlds interpretation, metaphysical, microwave background radiation, modal realism, multiple histories, observable universe, ontological, oscillatory universe, physical constants, possible worlds, quantum foam, quantum indeterminacy, quantum loop gravity, quantum mechanics, quantum multiverse, quantum superposition, science fiction, scientific investigation, simulated world, space, string landscape, string theory, tautology, testability, unfalsifiable, universes, wave function collapse, wormholes
 Adapted from the Wikipedia article "Multiverse hypotheses in physics", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki |
