Brane cosmology refers to several theories in particle physics and cosmology related to string theory, superstring theory and M-theory. Brane and bulk The central idea is that the visible, four-dimensional universe is restricted to a brane inside a higher-dimensional space, called the "bulk" (also known as "hyperspace"). Why gravity is weak and the cosmological constant is small Some versions of brane cosmology, based on the large extra dimension idea, can explain the weakness of gravity relative to the other fundamental forces of nature, thus solving the so-called hierarchy problem. Models of brane cosmology One of the earliest documented attempts to apply brane cosmology as part of a conceptual theory is dated to 1983. The authors discussed the possibility that the Universe has dimensions, but ordinary particles are confined in a potential well which is narrow along spatial directions and flat along three others, and proposed a particular five-dimensional model.
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The Inflationary universeJohn C. LillyJohn Cunningham Lilly (January 6, 1915 – September 30, 2001) was a American physician, neuroscientist, psychoanalyst, psychonaut, philosopher, writer and inventor. He was a researcher of the nature of consciousness using mainly isolation tanks, dolphin communication, and psychedelic drugs, sometimes in combination. Early life and education John Lilly was born to a wealthy family on January 6, 1915, in Saint Paul, Minnesota. His father was Richard Coyle Lilly, president of the First National Bank of St. Paul. Lilly showed an interest in science at an early age. While at St. Despite his father's wishes for him to go to an eastern Ivy-league college to become a banker, Lilly accepted a scholarship at the California Institute of Technology to study science. In 1934, Lilly read Aldous Huxley's Brave New World. Lilly became engaged to his first wife, Mary Crouch, at the beginning of his junior year at Caltech. At the University of Pennsylvania, Lilly met a professor named H. S.E.T.I.
The Brane multiverseQuantum informationIn physics and computer science, quantum information is information that is held in the state of a quantum system. Quantum information is the basic entity that is studied in the growing field of quantum information theory, and manipulated using the engineering techniques of quantum information processing. Much like classical information can be processed with digital computers, transmitted from place to place, manipulated with algorithms, and analyzed with the mathematics of computer science, so also analogous concepts apply to quantum information. Quantum information Quantum information differs strongly from classical information, epitomized by the bit, in many striking and unfamiliar ways. A unit of quantum information is the qubit. The study of all of the above topics and differences comprises quantum information theory. Quantum information theory The theory of quantum information is a result of the effort to generalize classical information theory to the quantum world.
Eternal inflationEternal inflation is predicted by many different models of cosmic inflation. MIT professor Alan H. Guth proposed an inflation model involving a "false vacuum" phase with positive vacuum energy. Parts of the Universe in that phase inflate, and only occasionally decay to lower-energy, non-inflating phases or the ground state. In chaotic inflation, proposed by physicist Andrei Linde, the peaks in the evolution of a scalar field (determining the energy of the vacuum) correspond to regions of rapid inflation which dominate. Alan Guth's 2007 paper, "Eternal inflation and its implications", details what is now known on the subject, and demonstrates that this particular flavor of inflationary universe theory is relatively current, or is still considered viable, more than 20 years after its inception.  Inflation and the multiverse Both Linde and Guth believe that inflationary models of the early universe most likely lead to a multiverse but more proof is required. History
String theoryString theory was first studied in the late 1960s as a theory of the strong nuclear force before being abandoned in favor of the theory of quantum chromodynamics. Subsequently, it was realized that the very properties that made string theory unsuitable as a theory of nuclear physics made it a promising candidate for a quantum theory of gravity. Five consistent versions of string theory were developed until it was realized in the mid-1990s that they were different limits of a conjectured single 11-dimensional theory now known as M-theory. Many theoretical physicists, including Stephen Hawking, Edward Witten and Juan Maldacena, believe that string theory is a step towards the correct fundamental description of nature: it accommodates a consistent combination of quantum field theory and general relativity, agrees with insights in quantum gravity (such as the holographic principle and black hole thermodynamics) and has passed many non-trivial checks of its internal consistency.
The quilted universeStanding waveTwo opposing waves combine to form a standing wave. For waves of equal amplitude traveling in opposing directions, there is on average no net propagation of energy. Moving medium As an example of the first type, under certain meteorological conditions standing waves form in the atmosphere in the lee of mountain ranges. Standing waves and hydraulic jumps also form on fast flowing river rapids and tidal currents such as the Saltstraumen maelstrom. Opposing waves In practice, losses in the transmission line and other components mean that a perfect reflection and a pure standing wave are never achieved. Another example is standing waves in the open ocean formed by waves with the same wave period moving in opposite directions. Mathematical description In one dimension, two waves with the same frequency, wavelength and amplitude traveling in opposite directions will interfere and produce a standing wave or stationary wave. and where: Examples Sound waves Light
Cyclic modelA cyclic model (or oscillating model) is any of several cosmological models in which the universe follows infinite, or indefinite, self-sustaining cycles. For example, the oscillating universe theory briefly considered by Albert Einstein in 1930 theorized a universe following an eternal series of oscillations, each beginning with a big bang and ending with a big crunch; in the interim, the universe would expand for a period of time before the gravitational attraction of matter causes it to collapse back in and undergo a bounce. Overview In the 1920s, theoretical physicists, most notably Albert Einstein, considered the possibility of a cyclic model for the universe as an (everlasting) alternative to the model of an expanding universe. However, work by Richard C. One new cyclic model is a brane cosmology model of the creation of the universe, derived from the earlier ekpyrotic model. Other cyclic models include Conformal cyclic cosmology and Loop quantum cosmology. See also
The Physics ClassroomThe Cyclic multiverseString theory landscapeThe string theory landscape refers to the huge number of possible false vacua in string theory. The large number of theoretically allowed configurations has prompted suggestions that certain physical mysteries, particularly relating to the fine-tuning of constants like the cosmological constant or the Higgs boson mass, may be explained not by a physical mechanism but by assuming that many different vacua are physically realized. The anthropic landscape thus refers to the collection of those portions of the landscape that are suitable for supporting intelligent life, an application of the anthropic principle that selects a subset of the otherwise possible configurations. Anthropic principle Bayesian probability Some physicists, starting with Weinberg, have proposed that Bayesian probability can be used to compute probability distributions for fundamental physical parameters, where the probability of observing some fundamental parameters is given by, where and . Criticism
The Landscape multiverseMany-worlds interpretationThe quantum-mechanical "Schrödinger's cat" paradox according to the many-worlds interpretation. In this interpretation, every event is a branch point; the cat is both alive and dead, even before the box is opened, but the "alive" and "dead" cats are in different branches of the universe, both of which are equally real, but which do not interact with each other. The many-worlds interpretation is an interpretation of quantum mechanics that asserts the objective reality of the universal wavefunction and denies the actuality of wavefunction collapse. The original relative state formulation is due to Hugh Everett in 1957. Later, this formulation was popularized and renamed many-worlds by Bryce Seligman DeWitt in the 1960s and 1970s. The decoherence approaches to interpreting quantum theory have been further explored and developed, becoming quite popular. Before many-worlds, reality had always been viewed as a single unfolding history. Outline Wojciech H.