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Quintom Scenario
The Quintom scenario (derived from the words '' quintessence'' and ''phantom'', as in phantom energy) is a hypothetical model of dark energy. Equation of State In this scenario, the equation of state p = w\rho of the dark energy, relating its pressure and energy density, can cross the boundary w = -1 associated with the cosmological constant. The boundary separates the phantom-energy-like behavior with w -1. 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. The Quintom scenario was applied in 2008 to produce a model of inflationary cosmology 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 seconds after the conjectured Big Bang singularit ... with a Big Bounce instead of a Big Bang singularity. References External links Dark Energ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quintessence (physics)
In physics, quintessence is a hypothetical form of dark energy, more precisely a scalar field, postulated as an explanation of the observation of an accelerating rate of expansion of the universe. The first example of this scenario was proposed by Ratra and Peebles (1988) and Wetterich (1988). The concept was expanded to more general types of time-varying dark energy, and the term "quintessence" was first introduced in a 1998 paper by Robert R. Caldwell, Rahul Dave and Paul Steinhardt. It has been proposed by some physicists to be a fifth fundamental force. Quintessence differs from the cosmological constant explanation of dark energy in that it is dynamic; that is, it changes over time, unlike the cosmological constant which, by definition, does not change. Quintessence can be either attractive or repulsive depending on the ratio of its kinetic and potential energy. Those working with this postulate believe that quintessence became repulsive about ten billion years ago, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phantom Energy
Phantom energy is a hypothetical form of dark energy satisfying the equation of state with w < -1. It possesses negative kinetic energy, and predicts expansion of the universe in excess of that predicted by a , which leads to a . The idea of phantom energy is often dismissed, as it would suggest that the is with |
Dark Energy
In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the universe does not expand at a constant rate; rather, the universe's expansion is accelerating. Understanding the universe's evolution requires knowledge of its starting conditions and composition. Before these observations, scientists thought that all forms of matter and energy in the universe would only cause the expansion to slow down over time. Measurements of the cosmic microwave background (CMB) suggest the universe began in a hot Big Bang, from which general relativity explains its evolution and the subsequent large-scale motion. Without introducing a new form of energy, there was no way to explain how scientists could measure an accelerating universe. Since the 1990s, dark energy has been the most accepted premise to account for the acce ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equation Of State (cosmology)
In cosmology, the equation of state of a perfect fluid is characterized by a dimensionless number w, equal to the ratio of its pressure p to its energy density \rho: w \equiv \frac. It is closely related to the thermodynamic equation of state and ideal gas law. The equation The perfect gas equation of state may be written as p = \rho_m RT = \rho_m C^2 where \rho_m is the mass density, R is the particular gas constant, T is the temperature and C=\sqrt is a characteristic thermal speed of the molecules. Thus w \equiv \frac = \frac = \frac\approx 0 where c is the speed of light, \rho = \rho_mc^2 and C\ll c for a "cold" gas. FLRW equations and the equation of state The equation of state may be used in Friedmann–Lemaître–Robertson–Walker (FLRW) equations to describe the evolution of an isotropic universe filled with a perfect fluid. If a is the scale factor then \rho \propto a^. If the fluid is the dominant form of matter in a flat universe, then a \propto t^, where t is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and even by industry. Further, both spellings are often used ''within'' a particular industry or country. Industries in British English-speaking countries typically use the "gauge" spelling. is the pressure relative to the ambient pressure. Various units are used to express pressure. Some of these derive from a unit of force divided by a unit of area; the SI unit of pressure, the pascal (Pa), for example, is one newton per square metre (N/m2); similarly, the pound-force per square inch (psi) is the traditional unit of pressure in the imperial and U.S. customary systems. Pressure may also be expressed in terms of standard atmospheric pressure; the atmosphere (atm) is equal to this pressure, and the torr is defined as of this. Manometric u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Energy Density
In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It is sometimes confused with energy per unit mass which is properly called specific energy or . Often only the ''useful'' or extractable energy is measured, which is to say that inaccessible energy (such as rest mass energy) is ignored. In cosmological and other general relativistic contexts, however, the energy densities considered are those that correspond to the elements of the stress–energy tensor and therefore do include mass energy as well as energy densities associated with pressure. Energy per unit volume has the same physical units as pressure and in many situations is synonymous. For example, the energy density of a magnetic field may be expressed as and behaves like a physical pressure. Likewise, the energy required to compress a gas to a certain volume may be determined by multiplying the difference between the gas pressure and the external pressure by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
No-go Theorem
In theoretical physics, a no-go theorem is a theorem that states that a particular situation is not physically possible. Specifically, the term describes results in quantum mechanics like Bell's theorem and the Kochen–Specker theorem that constrain the permissible types of Hidden variable theory, hidden variable theories which try to explain the apparent randomness of quantum mechanics as a deterministic model featuring hidden states. Instances of no-go theorems Full descriptions of the no-go theorems named below are given in other articles linked to their names. A few of them are broad, general categories under which several theorems fall. Other names are broad and general-sounding but only refer to a single theorem. * Antidynamo theorems is a general category of theorems that restrict the type of magnetic fields that can be produced by dynamo theory, dynamo action. ** Cowling's theorem states that an axisymmetric magnetic field cannot be maintained through a self-sustaining ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inflationary Cosmology
In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of the universe, expansion of space in the early universe. The inflationary epoch lasted from seconds after the conjectured Big Bang singularity to some time between and 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 (5.4 billion years ago). Inflation theory was developed in the late 1970s and early 80s, with notable contributions by several theoretical physics, theoretical physicists, including Alexei Starobinsky at Landau Institute for Theoretical Physics, Alan Guth at Cornell University, and Andrei Linde at Lebedev Physical Institute. Alexei Starobinsky, Alan Guth, and Andrei Linde won the 2014 Kavli Prize "for pioneering the theory of cosmic i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Big Bounce
The Big Bounce is a hypothesized cosmological model for the origin of the known universe. It was originally suggested as a phase of the ''cyclic model'' or ''oscillatory universe'' interpretation of the Big Bang, where the first cosmological event was the result of the collapse of a previous universe. It receded from serious consideration in the early 1980s after inflation theory emerged as a solution to the horizon problem, which had arisen from advances in observations revealing the large-scale structure of the universe. In the early 2000s, inflation was found by some theorists to be problematic and unfalsifiable in that its various parameters could be adjusted to fit any observations, so that the properties of the observable universe are a matter of chance. Alternative pictures including a Big Bounce may provide a predictive and falsifiable possible solution to the horizon problem, and are under active investigation as of 2017. Expansion and contraction The concept of the B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Big Bang
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. Crucially, these models are compatible with the Hubble–Lemaître law—the observation that the farther away a galaxy is, the faster it is mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dark Energy
In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the universe does not expand at a constant rate; rather, the universe's expansion is accelerating. Understanding the universe's evolution requires knowledge of its starting conditions and composition. Before these observations, scientists thought that all forms of matter and energy in the universe would only cause the expansion to slow down over time. Measurements of the cosmic microwave background (CMB) suggest the universe began in a hot Big Bang, from which general relativity explains its evolution and the subsequent large-scale motion. Without introducing a new form of energy, there was no way to explain how scientists could measure an accelerating universe. Since the 1990s, dark energy has been the most accepted premise to account for the acce ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Énergie Fantôme
Énergie is a Canadian radio network of French-language mainstream rock outlets broadcasting throughout the province of Quebec and portions of eastern Ontario, in Eastern Canada. They offer a personality-driven mix of francophone and anglophone classic rock and alternative rock songs, catering to a young adult audience. Although the flagship station is CKMF-FM Montreal, the 10 stations in the network usually have their own talent and format for each of their own markets. They are owned by Bell Media. Most "Énergie" stations broadcast in the same markets as Bell's adult contemporary network Rouge FM. History In December 1988, "Énergie" was created. In 2006, Astral Media programmed a satellite radio channel, branded as Énergie2, for broadcast on Sirius Canada and Sirius Satellite Radio, on channel 89. This channel offered essentially the same format as the terrestrial network, and was hosted by Richard Fortin and Nicolas Wilson. However, the Énergie brand was entirely discarde ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
