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Vaidya Metric
In general relativity, the Vaidya metric describes the non-empty external spacetime of a spherically symmetric and nonrotating star which is either emitting or absorbing null dusts. It is named after the Indian physicist Prahalad Chunnilal Vaidya and constitutes the simplest non-static generalization of the non-radiative Schwarzschild solution to Einstein's field equation, and therefore is also called the "radiating(shining) Schwarzschild metric". From Schwarzschild to Vaidya metrics The Schwarzschild metric as the static and spherically symmetric solution to Einstein's equation reads To remove the coordinate singularity of this metric at r=2M, one could switch to the Eddington–Finkelstein coordinates. Thus, introduce the "retarded(/outgoing)" null coordinate u by and Eq(1) could be transformed into the "retarded(/outgoing) Schwarzschild metric" or, we could instead employ the "advanced(/ingoing)" null coordinate v by so Eq(1) becomes the "advanced(/ingoing) Schwarzschi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
General Relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the ' is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of second order partial differential equations. Newton's law of universal gravitation, which describes classical gravity, can be seen as a prediction of general relativity for the almost flat spacetime geometry around stationary mass distributions. Some predictions of general relativity, however, are beyond Newton's law of universal gra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rest Mass
The invariant mass, rest mass, intrinsic mass, proper mass, or in the case of bound systems simply mass, is the portion of the total mass of an object or system of objects that is independent of the overall motion of the system. More precisely, it is a characteristic of the system's total energy and momentum that is the same in all frames of reference related by Lorentz transformations.Lawrence S. LernerPhysics for Scientists and Engineers, Volume 2, page 1073 1997. If a center-of-momentum frame exists for the system, then the invariant mass of a system is equal to its total mass in that "rest frame". In other reference frames, where the system's momentum is nonzero, the total mass (a.k.a. relativistic mass) of the system is greater than the invariant mass, but the invariant mass remains unchanged. Because of mass–energy equivalence, the rest energy of the system is simply the invariant mass times the speed of light squared. Similarly, the total energy of the system is its to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Four-velocity
In physics, in particular in special relativity and general relativity, a four-velocity is a four-vector in four-dimensional spacetimeTechnically, the four-vector should be thought of as residing in the tangent space of a point in spacetime, spacetime itself being modeled as a smooth manifold. This distinction is significant in general relativity. that represents the relativistic counterpart of velocity, which is a three-dimensional vector in space. Physical events correspond to mathematical points in time and space, the set of all of them together forming a mathematical model of physical four-dimensional spacetime. The history of an object traces a curve in spacetime, called its world line. If the object has mass, so that its speed is necessarily less than the speed of light, the world line may be parametrized by the proper time of the object. The four-velocity is the rate of change of four-position with respect to the proper time along the curve. The velocity, in contrast, is t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
World Line
The world line (or worldline) of an object is the path that an object traces in 4-dimensional spacetime. It is an important concept in modern physics, and particularly theoretical physics. The concept of a "world line" is distinguished from concepts such as an "orbit" or a "trajectory" (e.g., a planet's ''orbit in space'' or the ''trajectory'' of a car on a road) by the ''time'' dimension, and typically encompasses a large area of spacetime wherein perceptually straight paths are recalculated to show their ( relatively) more absolute position states—to reveal the nature of special relativity or gravitational interactions. The idea of world lines originates in physics and was pioneered by Hermann Minkowski. The term is now most often used in relativity theories (i.e., special relativity and general relativity). Usage in physics In physics, a world line of an object (approximated as a point in space, e.g., a particle or observer) is the sequence of spacetime events corresp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proper Time
In relativity, proper time (from Latin, meaning ''own time'') along a timelike world line is defined as the time as measured by a clock following that line. It is thus independent of coordinates, and is a Lorentz scalar. The proper time interval between two events on a world line is the change in proper time. This interval is the quantity of interest, since proper time itself is fixed only up to an arbitrary additive constant, namely the setting of the clock at some event along the world line. The proper time interval between two events depends not only on the events, but also the world line connecting them, and hence on the motion of the clock between the events. It is expressed as an integral over the world line (analogous to arc length in Euclidean space). An accelerated clock will measure a smaller elapsed time between two events than that measured by a non-accelerated (inertial) clock between the same two events. The twin paradox is an example of this effect. By convention ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
William Morris Kinnersley
William Morris Kinnersley is an American physicist who is well known for his contributions to general relativity. Kinnersley earned his Ph.D. from Caltech in 1968, under the direction of Jon Mathews. In 1969, he published an exact null dust solution to the Einstein field equation and thereby created the photon rocket A photon rocket is a rocket that uses thrust from the momentum of emitted photons ( radiation pressure by emission) for its propulsion. Photon rockets have been discussed as a propulsion system that could make interstellar flight possible, which r ..., an object with mass propelled by the emission of light (radiation without mass). This solution remains one of the few known exact solutions with clear physical interpretations, and in consequence it is widely cited as an important breakthrough. In 1978, Kinnersley, C. Hoenselaers, and Basilis C. Xanthopoulos published an important solution generating method for solving the Einstein field equation. References * . ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weyl Metrics
In general relativity, the Weyl metrics (named after the German-American mathematician Hermann Weyl) are a class of ''static'' and ''axisymmetric'' solutions to Einstein's field equation. Three members in the renowned Kerr–Newman family solutions, namely the Schwarzschild, nonextremal Reissner–Nordström and extremal Reissner–Nordström metrics, can be identified as Weyl-type metrics. Standard Weyl metrics The Weyl class of solutions has the generic formJeremy Bransom Griffiths, Jiri Podolsky. ''Exact Space-Times in Einstein's General Relativity''. Cambridge: Cambridge University Press, 2009. Chapter 10.Hans Stephani, Dietrich Kramer, Malcolm MacCallum, Cornelius Hoenselaers, Eduard Herlt. ''Exact Solutions of Einstein's Field Equations''. Cambridge: Cambridge University Press, 2003. Chapter 20. where \psi(\rho,z) and \gamma(\rho,z) are two metric potentials dependent on ''Weyl's canonical coordinates'' \. The coordinate system \ serves best for symmetries of Weyl's space ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Killing Vector Field
In mathematics, a Killing vector field (often called a Killing field), named after Wilhelm Killing, is a vector field on a Riemannian manifold (or pseudo-Riemannian manifold) that preserves the metric tensor, metric. Killing fields are the Lie group#The Lie algebra associated to a Lie group, infinitesimal generators of isometry, isometries; that is, flow (geometry), flows generated by Killing fields are Isometry (Riemannian geometry), continuous isometries of the manifold. More simply, the flow generates a symmetry, in the sense that moving each point of an object the same distance in the direction of the Killing vector will not distort distances on the object. Definition Specifically, a vector field ''X'' is a Killing field if the Lie derivative with respect to ''X'' of the metric ''g'' vanishes: :\mathcal_ g = 0 \,. In terms of the Levi-Civita connection, this is :g\left(\nabla_Y X, Z\right) + g\left(Y, \nabla_Z X\right) = 0 \, for all vectors ''Y'' and ''Z''. In local c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Event Horizon
In astrophysics, an event horizon is a boundary beyond which events cannot affect an observer. Wolfgang Rindler coined the term in the 1950s. In 1784, John Michell proposed that gravity can be strong enough in the vicinity of massive compact objects that even light cannot escape. At that time, the Newtonian theory of gravitation and the so-called corpuscular theory of light were dominant. In these theories, if the escape velocity of the gravitational influence of a massive object exceeds the speed of light, then light originating inside or from it can escape temporarily but will return. In 1958, David Finkelstein used general relativity to introduce a stricter definition of a local black hole event horizon as a boundary beyond which events of any kind cannot affect an outside observer, leading to information and firewall paradoxes, encouraging the re-examination of the concept of local event horizons and the notion of black holes. Several theories were subsequently developed, s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Construction Of A Complex Null Tetrad
Calculations in the Newman–Penrose (NP) formalism of general relativity normally begin with the construction of a complex null tetrad \, where \ is a pair of ''real'' null vectors and \ is a pair of ''complex'' null vectors. These tetrad vectors respect the following normalization and metric conditions assuming the spacetime signature (-,+,+,+): *l_a l^a=n_a n^a=m_a m^a=\bar_a \bar^a=0\,; *l_a m^a=l_a \bar^a=n_a m^a=n_a \bar^a=0\,; *l_a n^a=l^a n_a=-1\,,\;\; m_a \bar^a=m^a \bar_a=1\,; *g_=-l_a n_b - n_a l_b +m_a \bar_b +\bar_a m_b\,, \;\; g^=-l^a n^b - n^a l^b +m^a \bar^b +\bar^a m^b\,. Only after the tetrad \ gets constructed can one move forward to compute the directional derivatives, spin coefficients, commutators, Weyl-NP scalars \Psi_i, Ricci-NP scalars \Phi_ and Maxwell-NP scalars \phi_i and other quantities in NP formalism. There are three most commonly used methods to construct a complex null tetrad: # All four tetrad vectors are nonholonomic combination ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
