共查询到20条相似文献,搜索用时 31 毫秒
1.
J. A. Belinchón 《Astrophysics and Space Science》2006,302(1-4):161-170
It is investigated the behaviour of the “constants” G, c and Λ in the framework of a perfect fluid LRS Bianchi I cosmological model. It has been taken into account the effects of
a c-variable into the curvature tensor. Two exact cosmological solutions are investigated, arriving t the conclusion that if
q < 0 (deceleration parameter) then G, c are growing functions on time t while Λ is a negative decreasing function on time. 相似文献
2.
José Antonio Belinchón 《Astrophysics and Space Science》2009,323(3):307-315
We study a massive cosmic strings with BII symmetries cosmological models in two contexts. The first of them is the standard
one with a barotropic equation of state. In the second one we explore the possibility of taking into account variable “constants”
(G and Λ). Both models are studied under the self-similar hypothesis. We put special emphasis in calculating the numerical values
for the equations of state. We find that for ω∈(0,1], G, is a growing time function while Λ, behaves as positive decreasing time function. If ω=0, both “constants”, G and Λ, behave as true constants. 相似文献
3.
Antonio Alfonso-Faus 《Astrophysics and Space Science》2010,325(1):113-117
We present a necessary and sufficient condition for an object of any mass m to be a quantum black hole (q.b.h.): “The product of the cosmological constant Λ and the Planck’s constant
ℏ, Λ and ℏ
corresponding to the scale defined by this q.b.h., must be of order one in a certain universal system of units”. In this system the numerical values known for Λ are of order one in cosmology and about 10122 for Planck’s scale. Proving that in this system the value of the cosmological ℏ
c
is of order one, while the value of ℏ for the Planck’s scale is about 10−122, both scales satisfy the condition to be a q.b.h., i.e. Λℏ≈1. In this sense the Universe is a q.b.h. We suggest that these objects, being q.b.h.’s, give us the linkage between thermodynamics,
quantum mechanics, electromagnetism and general relativity, at least for the scale of a closed Universe and for the Planck’s
scale. A mathematical transformation may refer these scales as corresponding to infinity (our universe) and zero (Planck’s
universe), in a “scale relativity” sense. 相似文献
4.
José Antonio Belinchón 《Astrophysics and Space Science》2012,338(2):381-400
We study how the constants G and Λ may vary in different theoretical models (general relativity with a perfect fluid, scalar cosmological models (“quintessence”)
with and without interacting scalar and matter fields and a scalar-tensor model with a dynamical Λ) in order to explain some
observational results. We apply the program outlined in section II to study three different geometries which generalize the
FRW ones, which are Bianchi V, VII0 and IX, under the self-similarity hypothesis. We put special emphasis on calculating exact power-law solutions which allow
us to compare the different models. In all the studied cases we arrive at the conclusion that the solutions are isotropic
and noninflationary while the cosmological constant behaves as a positive decreasing time function (in agreement with the
current observations) and the gravitational constant behaves as a growing time function. 相似文献
5.
V. A. Kotov 《Bulletin of the Crimean Astrophysical Observatory》2011,107(1):70-77
The hypothesis that some extragalactic objects pulsate with a period of P
0 = 9600.606(12) s, which was first discovered in the Sun, is tested with data on quasar 3C 273. Observations of its rapid
photometric variability were made by different observers in 1968–2005 within several spectral bands. At the 4σ confidence
level, these data show that there is a period of 9600.624(18) s, which is consistent, within the error limits, with P
0 (mean harmonic amplitude 0.006 B magnitude). Its independence from the redshift z is a sign of a cosmological origin of the P
0 pulsation, which is sometimes understood as the “rhythm” of cosmos’ absolute time. This phenomenon is also shown to be deeply
connected—via the Sanchez formula—to the fundamental constants of physics and cosmology. This refutes the standard Big Bang
hypothesis and confirms the Steady State, c-free model of the Universe (c is the speed of light). 相似文献
6.
7.
8.
In this paper, the generalized second law (GSL) of thermodynamics and entropy is revisited in the context of cosmological
models with bouncing behavior such as chameleon cosmology where the boundary of the universe is assumed to be enclosed by
the dynamical apparent horizon. From a thermodynamic point of view, to link between thermodynamic and geometric parameters
in cosmological models, we introduce “entropy rate of change multiplied by the temperature” as a model independent thermodynamic
state parameter together with the well known {r,s} statefinder to differentiate the dark energy models. 相似文献
9.
A perturbation in the ratio of the matter temperature to the radiation temperature in the form of a Gaussian with amplitude
A and width σ (in units of the redshift z) centered at some redshift z
c is considered, with some “standard” temperature ratio obtained from a simultaneous solution of the cosmological recombination
kinetics and energy equations being taken as the initial (unperturbed) one. Comparatively small (A = ± 0.01), fast (σ = 17) perturbations are shown to give rise to distinct narrow absorption (for A > 0) or emission (for A < 0) quasi-lines in each of the subordinate continua. The positions of these quasi-lines correlate with the position of the
perturbation center, while their intensities are very sensitive to the perturbation amplitude. At the same time, the manifestation
of the perturbation is much less clear in hydrogen lines (subordinate ones and the Ly-α line) and two-photon emission. As a result, the full perturbed spectrum is characterized by the presence of the narrow quasi-lines
mentioned above and by a general decrease (for A > 0) or increase (for A < 0) in intensity with increasing wavelength. 相似文献
10.
Einstein’s field equations with variable gravitational and cosmological “constant” are considered in presence of perfect fluid
for Bianchi type-I space-time. Consequences of the four cases of the phenomenological decay of Λ have been discussed which
are consistent with observations. The physical significance of the cosmological models have also been discussed.
相似文献
11.
In 1968–2005 different observers (mainly, one of the authors—V.M. Lyuty) performed numerous measurements of luminosity of
the nucleus of the Seyfert galaxy NGC 4151. It is shown that (a) luminosity of the object pulsated over 38 years with a period of 160.0106(7) min coinciding, within the error limits, with
the well-known period P
0 = 160.0101(2) min of the enigmatic “solar” pulsations, and (b) when registering oscillations of luminosity of NGC 4151 nucleus with the P
0 period, time moments of observations must be reduced to the earth instead of the sun, i.e., to the reference frame of the
observer. The coherent P
0 oscillation is characterized, therefore, by invariability of both frequency and phase with respect to redshift z and the earth’s orbital motion, respectively. From these results it, thus, follows that the coherent P
0 oscillation seems to be of a true cosmological origin. The P
0 period itself might represent a course of the “cosmic clock” related to the existence of an absolute time of the Universe
in Newton’s comprehension. 相似文献
12.
M. Villata 《Astrophysics and Space Science》2012,339(1):7-12
The unexpected discovery of the accelerated cosmic expansion in 1998 has filled the Universe with the embarrassing presence
of an unidentified “dark energy”, or cosmological constant, devoid of any physical meaning. While this standard cosmology
seems to work well at the global level, improved knowledge of the kinematics and other properties of our extragalactic neighborhood
indicates the need for a better theory. We investigate whether the recently suggested repulsive-gravity scenario can account
for some of the features that are unexplained by the standard model. Through simple dynamical considerations, we find that
the Local Void could host an amount of antimatter (∼5×1015
M
⊙) roughly equivalent to the mass of a typical supercluster, thus restoring the matter-antimatter symmetry. The antigravity
field produced by this “dark repulsor” can explain the anomalous motion of the Local Sheet away from the Local Void, as well
as several other properties of nearby galaxies that seem to require void evacuation and structure formation much faster than
expected from the standard model. At the global cosmological level, gravitational repulsion from antimatter hidden in voids
can provide more than enough potential energy to drive both the cosmic expansion and its acceleration, with no need for an
initial “explosion” and dark energy. Moreover, the discrete distribution of these dark repulsors, in contrast to the uniformly
permeating dark energy, can also explain dark flows and other recently observed excessive inhomogeneities and anisotropies
of the Universe. 相似文献
13.
Emilio Santos 《Astrophysics and Space Science》2011,332(2):423-435
It is shown that quantum vacuum fluctuations give rise to a curvature of space-time equivalent to a cosmological constant,
that is a homogeneous energy density ρ and pressure p fulfilling −p=ρ>0. The fact that the fluctuations produce curvature, even if the vacuum expectation of the energy vanishes, is a consequence
of the non-linear character of the Einstein equation. A calculation is made, involving plausible hypotheses within quantized
gravity, which establishes a relation between the two-point correlation of the vacuum fluctuations and the space-time curvature.
Arguments are given which suggest that the density ρ might be of order the “dark energy” density currently assumed to explain the observed accelerated expansion of the universe. 相似文献
14.
C. P. Singh 《Astrophysics and Space Science》2011,331(1):337-342
The evolution and dynamics of a locally-rotationally-symmetric (LRS) Bianchi type-V space-time cosmological models are discussed
with variable gravitational and cosmological “constants” in context of the particle creation. We present the exact solutions
of Einstein field equations by using a power-law form of the average scale factor of the metric in the case of the particle
creation and in the absence of particle creation. The solution describes the particle and entropy generation in the anisotropic
cosmological models. The particle creation rate is uniquely determined by the variation of gravitational and cosmological
“constants”. We observe that the variable gravitational constant does not necessarily imply particle creation. In a generic
situation, models can be interpolated between different phases of the universe. The dynamical behaviors of the solutions and
kinematical parameters of the model are discussed in detail. 相似文献
15.
Mohamed E. Hassani 《Astrophysics and Space Science》2011,331(1):221-236
In this work, which is a supplemental to previous one, we undertake to establish some cosmological thermodynamic equations
in the context of the cyclical universe as the scenario in which the universe itself is considered like an adiabatic thermodynamical
system enclosed in physical volume characterized by periodic reversible transitions. Our model is based on the combination
of local and global cosmological time-dependent temperatures {T
0(τ
0),T(τ)} and volumes {V
0(τ
0),V(τ)} instead of the critical temperature T
c and volume V
c; and the infinitesimal relative variations {dT/T,dV/V}, which are mainly due to the cosmological chaotic fluctuations that are generally ignored in certain oscillating models.
By taking into account all these factors, certain equations in the form of d
ℓ/ℓ=±η
d
τ/τ
H have been established and from them we derive some others to provide a mechanism that is responsible for the thermodynamic
evolution of the cyclical universe. 相似文献
16.
Antonio Alfonso-Faus 《Astrophysics and Space Science》2012,337(1):363-365
Using the relation proposed by Weinberg in 1972, combining quantum and cosmological parameters, we prove that the self gravitational
potential energy of any fundamental particle is a quantum, with physical properties independent of the mass of the particle.
It is a universal quantum of gravitational energy, and its physical properties depend only on the cosmological scale factor
R and the physical constants ℏ and c. We propose a modification of the Weinberg’s relation, keeping the same numerical value, but substituting the cosmological
parameter H/c by 1/R. 相似文献
17.
Jean-Claude Pecker 《Journal of Astrophysics and Astronomy》1997,18(4):323-333
Still more shocking than the metaphysical assumption of some initial singularity, is the constant insistence upon the so-called
cosmological principle of “homogeneity” and “isotropy” of the Universe. Observations do contradict this principle. And to
me, the inhomogeneous, fractal at least on a certain scale range, of the distribution of matter is in itself an important
cosmological fact, hitherto almost neglected. Moreover difficultties as to the applicability of the second principle of thermodynamics,
observations of abnormal redshifts, etc., are casting large doubts not only upon the standard cosmological models, but even
on the interpretation of the observed redshift as due solely to a universal expansion. 相似文献
18.
The cosmological reconstruction of modified F(R) and F(G)F(\mathcal{G}) gravities with agegraphic dark energy (ADE) model in a spatially flat universe without matter field is investigated by using
e-folding “N” as a forward way. After calculating a consistent F(R) in ADE’s framework, we obtain conditions for effective equation of state parameter w
eff, and see that reconstruction is possible for both phantom and non-phantom era. These calculations also are done for F(G)F(\mathcal{G}) gravity and the condition for a consistent reconstruction is obtained. 相似文献
19.
Antonio Alfonso-Faus 《Astrophysics and Space Science》2009,321(1):69-72
It is shown that the usual choice of units obtained by taking G=c=ℏ=1, giving the Planck’s units of mass, length and time, introduces an artificial contradiction between cosmology and particle
physics: the lambda problem that we associate with ℏ. We note that the choice of ℏ=1 does not correspond to the scale of quantum physics. For this scale we prove that the correct value is ℏ≈1/10122, while the choice of ℏ=1 corresponds to the cosmological scale. This is due to the scale factor of 1061 that converts the Planck scale to the cosmological scale. By choosing the ratio G/c
3=constant=1, which includes the choice G=c=1, and the momentum conservation mc=constant, we preserve the derivation of the Einstein field equations from the action principle. Then the product Gm/c
2=r
g
, the gravitational radius of m, is constant. For a quantum black hole we prove that ℏ≈r
g
2≈(mc)2. We also prove that the product Λℏ is a general constant of order one, for any scale. The cosmological scale implies Λ≈ℏ≈1, while the Planck scale gives Λ≈1/ℏ≈10122. This explains the Λ problem. We get two scales: the cosmological quantum black hole (QBH), size ∼1028 cm, and the quantum black hole (qbh) that includes the fundamental particles scale, size ∼10−13 cm, as well as the Planck’ scale, size ∼10−33 cm.
相似文献
20.
Marcelo Samuel Berman 《Astrophysics and Space Science》2009,323(1):103-106
We present a lambda-Universe, in scalar-tensor gravity, reviewing Berman and Trevisan’s inflationary case (Berman and Trevisan
in Int. J. Theor. Phys., 2009) and then we find a solution for an accelerating power-law scale-factor.
The negativity of cosmic pressure implies acceleration of the expansion, even with Λ<0. The cosmological term, and the coupling
“constant”, are in fact, time-varying.
相似文献