共查询到20条相似文献，搜索用时 34 毫秒
1.
B. Kuchowicz 《Astrophysics and Space Science》1976,39(1):157-172
The Einstein-Cartan theory, which is a slight modification of the general theory of relativity, is almost indistinguishable in its practical consequences from the latter theory. A characteristic spin-spin repulsive interaction which is of some importance at ultraheavy densities, prevents the singularities occurring in the Einstein-Cartan treatment. It is shown how this mechanism of preventing the singularity applies to cosmological models in which the spins of matter are aligned along some symmetry axis. Some exact solutions without singularities of the relevant set of equations are obtained. 相似文献
2.
Vladimír Skalský 《Astrophysics and Space Science》2010,330(2):373-398
Assuming that the relativistic universe is homogeneous and isotropic, we can unambiguously determine its model and physical properties, which correspond with the Einstein general theory of relativity (and with its two special partial solutions: Einstein special theory of relativity and Newton gravitation theory), quantum mechanics, and observations, too. 相似文献
3.
Exact theory for expanding density perturbations under the following assumptions: (i) Friedmann universes made of dust only; (ii) spherically-symmetric perturbations (iii) isolated perturbations; (iv) null peculiar velocity field; is reviewed and extended. The overdensity equation is derived and the related solution is determined concerning both mean overdensity and local overdensity, and including both the growing and the decreasing mode, in terms of non-dimensional variables normalized to the initial configuration. A first-order and zero-order approximation to the exact theory is also performed in view of applications to specific problems, e.g., the acquisition of angular momentum by tidal torques. The idealized case presented here makes a necessary reference in dealing with more general situations involving both analytical and numerical approaches. 相似文献
4.
A. I. Shapiro 《Astrophysics》2002,45(2):215-222
A model problem in the theory of line formation in an optically thick, purely scattering, stellar atmosphere is considered. The integral equation of radiation transfer at line frequencies is solved numerically for a two-level atom in the approximation of complete frequency redistribution in scattering. The numerical results are compared with those calculated from equations of the asymptotic theory. On the basis of the asymptotic theory, the positions of intensity maxima in a line are found for different absorption profiles. 相似文献
5.
A form of planetary perturbation theory based on canonical equations of motion, rather than on the use of osculating orbital elements, is developed and applied to several problems of interest. It is proved that, with appropriately selected initial conditions on the orbital elements, the two forms of perturbation theory give rise to identical predictions for the observable coordinates and velocities, while the orbital elements themselves may be strikingly different. Differences between the canonical form of perturbation theory and the classical Lagrange planetary perturbation equations are discussed. The canonical form of perturbation theory in some cases has advantages when the perturbing forces are velocity-dependent, but the two forms of perturbation theory are equivalent if the perturbing forces are dependent only on position and not on velocity. The canonical form of the planetary perturbation equations are derived and applied to the Lense Thirring precession of a test body in a Keplerian orbit around a rotating mass source. 相似文献
6.
7.
We show that introducing torsion in general relativity, that is, physically, considering the effect of the spin, and linking the torsion to defects in the space-time topology we can have a minimum unit of time. In this context we have the possibility of identifying the defects in space-time topology induced by torsion as behaving like a string so that the minimum length, derived by treating the spin as an extra dimension, is related with string tension. Physical implications are considered for field theory (we can eliminate the divergence of self-energy integral without introducing anyad hoc cut-off), particle decay, evaporation of black holes, and information theory. 相似文献
8.
Vincent Icke 《Astrophysics and Space Science》1996,244(1-2):293-311
Our Universe consistes of particles, space and time. Ever since Descartes we have known that true emptiness cannot exist; ever since Einstein we have known that space and time are part of the stuff of our world. Efforts to determine the structure of particles go in parallel with the search for the structure of spacetime. Einstein gave us a geometrical answer regarding the structure of spacetime: a distance recipe (Lorentz-Minkowski) suffices. The theory boils down to a patching together of local Lorentz frames into a global whole, which gives it the form of a gauge field theory based on local Lorentz symmetry. On large scales, the Einstein Equation seems to work well. The structure of particles is described by a gauge field. too. On small scales the Standard Model seems to work very well.However, we know from Newtonian gravity that the presence of particles must be related to the structure of spacetime. Einstein made a conjecture for the form of this connection using the Newtonian limit of small speeds and weak fields. The right hand side of his equation for the bulk theory of matter (the energy-momentum tensor), is equated to the Einstein tensor from non-Euclidian geometry.But that connection is wrong. The structure of spacetime cannot be equated to the density of particles if we include the Standard Model in the matter tensor. In field theory a potential is not something that can be freely changed by adding an arbitrary scalar term; due to the local (as opposed to global) character of the fields, a potential becomes an entity in itself. Einstein's conjecture runs into profound trouble because the reality of potentials implies that the zero point energy of the vacuum must be included in the Einstein equation. The net result is the appearance of a term equivalent to a cosmological constant A of stupendous size, some 10118 times the critical cosmic density.The crisis due to the zero point fluctuations in the energy-momentum tensor is a clash of titans: Einstein's geometrical ideas on spacetime structure vs the behaviour of particles and the vacuum discribed by Dirac and followers. Someone, or everyone, is wrong. In my opinion the straightforward quantization of spacetime will always be impossible because the usual particle symmetries (U(1), SU(2), SU(3) and relatives) connect fermions and bosons, whereas relativistic analogies of these symmetries (the Lorentz symmetry) says something about spacetime and not about particles. 相似文献
9.
Probhas Ray Chaudhuri 《Astrophysics and Space Science》1971,12(2):325-328
The spectroscopic determination of the helium abundance in the oldest stars of the galaxy is supported by the theory of stellar evolution when neutrino emission is considered according to the photon-neutrino coupling theory, if it is assumed that the population II stars started their life with a low surface helium content.Receipt delayed by postal strike in Great Britain. 相似文献
10.
Cezary Migaszewski Krzysztof Go&#;dziewski 《Monthly notices of the Royal Astronomical Society》2008,388(2):789-802
We present the secular theory of coplanar N -planet system, in the absence of mean motion resonances between the planets. This theory relies on the averaging of a perturbation to the two-body problem over the mean longitudes. We expand the perturbing Hamiltonian in Taylor series with respect to the ratios of semimajor axes which are considered as small parameters, without direct restrictions on the eccentricities. Next, we average out the resulting series term by term. This is possible thanks to a particular but in fact quite elementary choice of the integration variables. It makes it possible to avoid Fourier expansions of the perturbing Hamiltonian. We derive high-order expansions of the averaged secular Hamiltonian (here, up to the order of 24) with respect to the semimajor axes ratio. The resulting secular theory is a generalization of the octupole theory. The analytical results are compared with the results of numerical (i.e. practically exact) averaging. We estimate the convergence radius of the derived expansions, and we propose a further improvement of the algorithm. As a particular application of the method, we consider the secular dynamics of three-planet coplanar system. We focus on stationary solutions in the HD 37124 planetary system. 相似文献
11.
marta Folgueira Jean Souchay Hiroshi Kinoshita 《Celestial Mechanics and Dynamical Astronomy》1998,70(3):147-157
In this paper, we make a study about the influence of the coefficients of the geopotential C4,m and S4,m, (m=1,2,3,4) on the nutation, starting from the Hamiltonian theory as developed by Kinoshita (1977).We obtain ten coefficients
larger than 0.05 μ as for the nutation in longitude and six for the nutation in obliquity. The present results are included
in the reconstruction of the theory of nutation (REN‐2000) at the level of truncation of 0.1 μ as (Souchay et al., 1997).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
Similarity theory, which is necessary in order to apply the results of laboratory astrophysics experiments to relativistic
astrophysical plasmas, is presented. The analytical predictions of the similarity theory are compared with PIC numerical simulations
and the most recent experimental data on monoenergetic electron acceleration in diluted plasmas and high harmonic generation
at overdense plasma boundaries. We demonstrate that similarity theory is a reliable tool for explaining a surprisingly wide
variety of laboratory plasma phenomena the predictions of which can be scaled up to astrophysical dimensions. 相似文献
13.
Jacques P. Vallée 《New Astronomy Reviews》2011,55(3-4):23-90
Here I present a survey of planetary, stellar and clumpy interstellar magnetic fields, with an emphasis on discoveries made in the last decade. Ground-based and Earth–satellite observations of magnetic fields in astronomical objects are cataloged, as obtained at all multiple electromagnetic wavelengths.For each type of object, the basic observational properties are summarized, and the best theoretical scenario which accounts for the large body of observations is discussed. There is no single unifying magnetic model for all objects (although dynamo theory comes close for many compact objects, and helical theory for many extended objects).The strength of the observed magnetic fields reaches exagauss values (1018 G) in compact objects such as magnetars, and decreases to microgauss values (10?6 G) in the clumpy interstellar medium. 相似文献
14.
《New Astronomy Reviews》2002,46(11):637-643
After an introduction relating to the late Dennis Sciama, I review the interlocked quantization programs of Gravity and Weyl Yang-Mills gauge theory, including the independent emergence of two superalgebraic systems: (a) Supersymmetry with supermultiplets relating multiplets of different Quantum Statistics: (b) superalgebraic extensions of the calculus of differential forms. The latter include the BRST unitarity-inducing constrains and a new tool, the Quillen Superconnection, with contributions from noncommutative geometry. Two examples are reviewed, one predicting the mass of the Higgs meson in Electroweak theory and the other relating to Riemannian Gravity emerging through a similar mechanism. 相似文献
15.
H.J. Melosh 《Icarus》1984,59(2):234-260
Recent discoveries suggest that some meteorites have originated from major planets or satellites. Although it has been suggested that a large primary impact event might eject rock fragments as secondaries, it was previously supposed that material ejected at several kilometers per second would be highly shocked or perhaps melted. It is shown that a small amount of material (0.01 to 0.05 projectile mass) may be ejected at high velocity shock pressures. The approach utilizes observations of stress-wave propagation from large underground explosions to predict stresses and particle velocities in the near-surface environment. The largest fragments ejected at any velocity are spalls that originate from the target planet's surface. The spall size is proportional to the radius of the primary impactor and the target tensile strength and inversely proportional to ejection velocity. The shock level in the spalls is low, typically half of the dynamic crushing strength of the rock. The model also predicts the aspect ratio of the spalled fragments, the angle of ejection, and the sizes and shock level of other fragments originating deeper in the target. Comparison with data from laboratory experiments, the Ries Crater, and secondary crater sizes shows generally good agreement, although the observed fragment size at ejection velocities greater than 1 km/sec is considerably smaller than the simple version of the theory predicts. The theory indicates that although significant masses of solid material could be ejected from the Moon or Mars by large meteorite impacts, the fragments ejected from ca. 30-km-diameter craters are at most a few tens of meters in diameter if the most optimistic assumptions are made. The maximum fragment diameter is more likely to be about a meter. This theory, however, applies rigorously only up to ejection velocities of ca 1 km/sec. Further numerical extensions are necessary before film conclusions can be drawn, especially for Martian ejecta. 相似文献
16.
Pavel Voráček 《Astrophysics and Space Science》1985,116(1):197-206
Mach's principle is formulated in two different ways, heuristic and mathematical. Known problems of the principle are listed and two of them, the problem of its validity in the case the Universe is open and the boundary condition problem, are analyzed separately. Moreover, the history of the cosmic potential is outlined and a short modification of Horák's deduction of the potential is presented together with a discussion on the conditions of the solution. The conclusions are drawn that the Universe is closed and that Mach's principle is compatible with the general theory of relativity, provided that the Big Bang did not start from a singularity but from finite volume and density. In the last section it is shown that Rosen's bimetric theory is compatible with our picture of the Universe. 相似文献
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18.
The exact solution is sought for the cosmological equations of Brans and Dicke's scalar-tensor theory when a power law exists between the gravitational constant and the radius of curvature of the universe. For the space of negative curvature no solution is possible. On the contrary for a closed space the gravitational constant and the radius of curvature increase linearly with respect to the age of the universe. The parameter of the scalar-tensor theory is necessarily negative and can be determined by the present values of the mass-density of the universe, the Hubble-constant and the gravitational constant. The solution has no analogy in Einstein's theory with vanishing cosmological constant, even when the deviations from Einstein's values of the solar relativistic effects are small. 相似文献
19.
Michael E. Hough 《Celestial Mechanics and Dynamical Astronomy》1981,25(2):111-136
An improved theory is presented of long period perigee motion for orbits near the critical inclinations 63.4° and 116.6°. Inclusion of lunisolar perturbations andall measured zonal harmonic coefficients from a recent Earth model are significant improvements over existing theories. Phase portraits are used to depict the interaction between eccentricity magnitude and argument of perigee. The Hamiltonian constant can be chosen as the parameter to display a family of phase plane trajectories consisting of libration, circulation, and asymptotic motion along separatrices near equilibrium points. A two parameter family of phase portraits is defined by the other two integrals, the average semimajor axis and component of angular momentum resolved along the Earth's polar axis. There are regions of the parameter space where the stability and total number of equilibria can change, or two separatrices can coalesce. These phenomena signal large qualitative changes in phase portrait topology. Numerical studies show that lunisolar perturbations control stability of equilibria for orbits with semimajor axes exceeding 1.4 Earth radii. Moreover, a theory which includes lunisolar perturbations predicts larger maximum fluctuations in eccentricity and faster oscillations near stable equilibria compared to a theory which models only the zonal harmonics. 相似文献
20.
I. A. Klimishin 《Astrophysics and Space Science》1973,22(1):3-12
The regularities of strong thermal waves moving in non-uniform media are considered in some detail. The application of thermal wave theory to Nova outburst interpretation is discussed. 相似文献