Quintom scenario

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The Quintom scenario (derived from the words quintessence and phantom, as in phantom energy) is a hypothetical model of dark energy.

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Equation of State

In this scenario, the equation of state of the dark energy, relating its pressure and energy density, can cross the boundary associated with the cosmological constant. The boundary separates the phantom-energy-like behavior with from the quintessence-like behavior with . A no-go theorem shows that this behavior requires at least two degrees of freedom for dark energy models involving ideal gases or scalar fields. [1]

The Quintom scenario was applied in 2008 to produce a model of inflationary cosmology with a Big Bounce instead of a Big Bang singularity. [2]

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The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the earliest known periods through its subsequent large-scale form. These models offer a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, and large-scale structure. The overall uniformity of the Universe, known as the flatness problem, is explained through cosmic inflation: a sudden and very rapid expansion of space during the earliest moments. However, physics currently lacks a widely accepted theory of quantum gravity that can successfully model the earliest conditions of the Big Bang.

<span class="mw-page-title-main">Physical cosmology</span> Branch of cosmology which studies mathematical models of the universe

Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood.

<span class="mw-page-title-main">Inflation (cosmology)</span> Theory of rapid universe expansion

In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from 10−36 seconds after the conjectured Big Bang singularity to some time between 10−33 and 10−32 seconds after the singularity. Following the inflationary period, the universe continued to expand, but at a slower rate. The acceleration of this expansion due to dark energy began after the universe was already over 7.7 billion years old.

<span class="mw-page-title-main">Cosmological constant</span> Constant representing stress–energy density of the vacuum

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<span class="mw-page-title-main">Accelerating expansion of the universe</span> Cosmological phenomenon

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<span class="mw-page-title-main">Big Crunch</span> Theoretical scenario for the ultimate fate of the universe

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<span class="mw-page-title-main">Big Bounce</span> Hypothetical cosmological model for the origin of the known universe

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Paul Joseph Steinhardt is an American theoretical physicist whose principal research is in cosmology and condensed matter physics. He is currently the Albert Einstein Professor in Science at Princeton University where he is on the faculty of both the Departments of Physics and of Astrophysical Sciences.

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<span class="mw-page-title-main">Dark energy</span> Unknown property in cosmology that causes the expansion of the universe to accelerate

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Sergei D. Odintsov is a Russian astrophysicist active in the fields of cosmology, quantum field theory and quantum gravity. Odintsov is an ICREA Research Professor at the Institut de Ciències de l'Espai (Barcelona) since 2003. He also collaborates as group leader at research projects of the Tomsk State Pedagogical University. He is editor-in-chief of Symmetry, and is a member of the editorial boards of Gravitation and Cosmology, International Journal of Geometric Methods in Modern Physics, International Journal of Modern Physics D, Journal of Gravity, Universe, and the Tomsk State Pedagogical University Bulletin. Odintsov also is an advisory panel member of Classical and Quantum Gravity.

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Entropic gravity, also known as emergent gravity, is a theory in modern physics that describes gravity as an entropic force—a force with macro-scale homogeneity but which is subject to quantum-level disorder—and not a fundamental interaction. The theory, based on string theory, black hole physics, and quantum information theory, describes gravity as an emergent phenomenon that springs from the quantum entanglement of small bits of spacetime information. As such, entropic gravity is said to abide by the second law of thermodynamics under which the entropy of a physical system tends to increase over time.

Horndeski's theory is the most general theory of gravity in four dimensions whose Lagrangian is constructed out of the metric tensor and a scalar field and leads to second order equations of motion. The theory was first proposed by Gregory Horndeski in 1974 and has found numerous applications, particularly in the construction of cosmological models of Inflation and dark energy. Horndeski's theory contains many theories of gravity, including General relativity, Brans-Dicke theory, Quintessence, Dilaton, Chameleon and covariant Galileon as special cases.

References

  1. Cai, Yi-Fu; Saridakis, Emmanuel N.; Setare, Mohammed R.; Xia, Jun-Qing (22 Apr 2010). "Quintom Cosmology - theoretical implications and observations". Physics Reports. 493 (1): 1–60. arXiv: 0909.2776 . Bibcode:2010PhR...493....1C. doi:10.1016/j.physrep.2010.04.001. S2CID   118866606.
  2. Cai, Yi-Fu; Qiu, Taotao; Xia, Jun-Qing; Zhang, Xinmin (2009). "A Model of Inflationary Cosmology Without Singularity". Physical Review D. 79 (2): 021303. arXiv: 0808.0819 . Bibcode:2009PhRvD..79b1303C. doi:10.1103/PhysRevD.79.021303. S2CID   118378803.