共查询到20条相似文献，搜索用时 15 毫秒
1.
Under assumption of the closed FRW-universe, the idea is presented that the cosmological expansion/contraction on its own, has an entropy balancing effectively the changing entropy of the cosmic fluid in such a way that at every epoch the total entropy of the Universe remains constant. 相似文献
2.
In this paper, the generalized second law (GSL) of thermodynamics and entropy is revisited in the context of cosmological
models in Gauss-Bonnet gravity with the boundary of the universe is assumed to be enclosed by the dynamical apparent horizon.
The model is best fitted with the observational data for distance modulus. The best fitted geometric and thermodynamic parameters
such as equation of state parameter, deceleration parameter and entropy are derived. To link between thermodynamic and geometric
parameters, the “entropy rate of change multiplied by the temperature” as a model independent thermodynamic state parameter
is also derived. The results show that the model is in good agreement with the observational analysis. 相似文献
3.
E. J. Lloyd-Davies T. J. Ponman D. B. Cannon 《Monthly notices of the Royal Astronomical Society》2000,315(4):689-702
Studies of the X-ray surface brightness profiles of clusters, coupled with theoretical considerations, suggest that the breaking of self-similarity in the hot gas results from an 'entropy floor', established by some heating process, which affects the structure of the intracluster gas strongly in lower-mass systems. By fitting analytical models for the radial variation in gas density and temperature to X-ray spectral images from the ROSAT PSPC and ASCA GIS, we have derived gas entropy profiles for 20 galaxy clusters and groups. We show that, when these profiles are scaled such that they should lie on top of one another in the case of self-similarity, the lowest-mass systems have higher-scaled entropy profiles than more massive systems. This appears to be due to a baseline entropy of depending on the extent to which shocks have been suppressed in low-mass systems. The extra entropy may be present in all systems, but is detectable only in poor clusters, where it is significant compared with the entropy generated by gravitational collapse. This excess entropy appears to be distributed uniformly with radius outside the central cooling regions.
We determine the energy associated with this entropy floor, by studying the net reduction in binding energy of the gas in low-mass systems, and find that it corresponds to a pre-heating temperature of 0.3 keV. Since the relationship between entropy and energy injection depends upon gas density, we are able to combine the excesses of 70140 keV cm2 and 0.3 keV to derive the typical electron density of the gas into which the energy was injected. The resulting value of implies that the heating must have happened prior to cluster collapse but after a redshift z 710. The energy requirement is well matched to the energy from supernova explosions responsible for the metals which now pollute the intracluster gas. 相似文献
We determine the energy associated with this entropy floor, by studying the net reduction in binding energy of the gas in low-mass systems, and find that it corresponds to a pre-heating temperature of 0.3 keV. Since the relationship between entropy and energy injection depends upon gas density, we are able to combine the excesses of 70140 keV cm
4.
In this study, we explore a particular type Hawking radiation which ends with zero temperature and entropy. The appropriate black holes for this purpose are the linear dilaton black holes. In addition to the black hole choice, a recent formalism in which the Parikh-Wilczek’s tunneling formalism amalgamated with quantum corrections to all orders in ? is considered. The adjustment of the coefficients of the quantum corrections plays a crucial role on this particular Hawking radiation. The obtained tunneling rate indicates that the radiation is not pure thermal anymore, and hence correlations of outgoing quanta are capable of carrying away information encoded within them. Finally, we show in detail that when the linear dilaton black hole completely evaporates through such a particular radiation, entropy of the radiation becomes identical with the entropy of the black hole, which corresponds to “no information loss”. 相似文献
5.
S. Nesslinger H. Drechsel R. Lorenz P. Harmanec P. Mayer M. Wolf 《Astrophysics and Space Science》2006,301(1-4):47-49
A Cosmological model with a viscous fluid in Kaluza-Klein metric is obtained assuming a time-dependent equation of state.
The solution is in fact a generalization of an earlier work by Hajj and Boutros for a perfect fluid. It is also found that
dimensional reduction of the extra space takes place such that the five-dimensional universe naturally evolves into an effective
four-dimensional one. The dynamical behavior of the model is examined and it is also found that with a decrease in extra space
the observable 3D space entropy increases thus accounting for the large value of entropy observable at present. 相似文献
6.
A homogeneous cosmological model in Kaluza–Klein metric is obtained assuming a time-dependent equation of state. The solution is in fact generalization of an earlier work by Hajj and Boutros for a perfect fluid. It is also found that dimensional reduction of the extra space takes place such that the five-dimensional universe naturally evolves into an effective four-dimensional one. The dynamical behaviour of the model is examined and it is also found that with a decrease in extra space the observable three-dimensional space entropy increase thus accounting for the large value of entropy observable at present. 相似文献
7.
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
8.
The cosmological event horizon entropy and the apparent horizon entropy of the ΛCDM and the Bianchi type I Universe model with viscosity has been calculated numerically, and analytically in the large time limit. It is shown that for these Universe models the cosmological event horizon entropy increases with time and for large times it approaches a finite maximum value. The effect of viscosity upon the entropy is also studied and we have found that its role is to decrease the entropy. The bigger the viscosity coefficient is the less the entropy will be. Furthermore, the radiation entropy for the ΛCDM Universe model with and without viscosity is investigated, and together with the cosmological event horizon entropy are used to examine the validity of the generalized second law of thermodynamics, which states that the total rate of change of entropy of the Universe is never negative, in this Universe model. 相似文献
9.
Using Unruh-Verlinde temperature obtained by entropic force, we directly calculate partition functions of quantum field in Schwarzschild spacetime via quantum statistical method and derive the expression of the black hole statistical entropy. In our calculation the lower limit of integral is the location of isolated horizon introduced in loop quantum gravity and the upper limit of integral is infinity. So the obtained entropy is the statistical entropy from isolated horizon to the infinite. In our calculation there are not the cutoff and approximation. The results showed that, as long as proper Immirzi parameters are selected, the entropy obtained by loop quantum gravity is consistent with the quantum statistical entropy outside the black hole horizon. Therefore the black hole entropy is a quantum entanglement entropy outside the isolated horizon. 相似文献
10.
The definition of the entropy of a cratered surface is given by analogy with the entropy of the information theory. The saturation, defined as the ratio between the area covered by craters of diameterD and the total observed area, is adopted as a measure of the probability to find a portion of a planetary surface covered by craters of the given diameterD.The meaning of such a new function is discussed in comparison with statistical approaches to the study of the cratering. Applications to Mercury are discussed.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy. 相似文献
11.
汪定雄 《中国天文和天体物理学报》1996,(1)
本文利用李立新和刘辽导出的黑洞视界附近的辐射态方程，计算了约束在一个球形盒子中的目引力辐射体系的墙（不含中心黑洞和含有中心黑洞两种情况）．与Sorkin等人的计算比较，本文的结果不会出现发散困难，而且体系的总摘（包括中心黑洞的墙）的上阳正好等于坍缩后形成的同质量的黑洞嫡．作者认为，自引力辐射体系坍绩的合理模式是先形成中心黑洞，然后中心黑洞逐渐长大直至整个体系全部坍缩为黑洞．在坍缩过程中，任一中间态的媳总是比末态的黑洞墙小，到坍缩过程结束总熵才等于对应的黑洞摘．这一结果为黑洞滴的起源提供了一个合理的解释． 相似文献
12.
Using the quantum statistical method, we calculate quantum statistical entropy between the black hole horizon and the cosmological horizon in Schwarzchild spacetime and derive the expression of quantum statistical entropy in de Sitter spacetime. Under the Unruh-Verlinde temperature of Schwarzchild-de Sitter spacetime in the entropic force views, we obtain the expression of quantum statistical entropy in de Sitter spacetime. It is shown that in de Sitter spacetime quantum statistical entropy is the sum of thermodynamic entropy corresponding black hole horizon and the one corresponding cosmological horizon. And the correction term of de Sitter spacetime entropy is obtained. Therefore, it is confirmed that the black hole entropy is the entropy of quantum field outside the black hole horizon. The entropy of de Sitter spacetime is the entropy of quantum field between the black hole horizon and the cosmological horizon. 相似文献
13.
本文利用共动度规讨论了非理想流体开放体系在自引力作用下的坍缩过程之熵变,结果表明,形成视界之前,体系的总熵不增,这说明黑洞的高熵产生于突变之中。 相似文献
14.
Exact solutions are obtained in a five-dimensional space-time with an energy-momentum tensor containing a viscous fluid, assuming either an equation of state or a special form for the viscous term in line with the assumption of Belinskii and Khalatnikov (1977). The solutions are, in fact, generalizations of an earlier work by Grøn for a perfect fluid in the 5D rest-mass varying theory of gravity proposed recently by Wesson. It is found that dimensional reduction of the extra space takes place in some of the cases such that the 5-dimensional universe naturally evolves into an effective 4-dimensional one. A huge amount of entropy can be produced following this shrinkage of extra-dimension which may account for the very large value of entropy per baryon observed in our 4D world. Moreover, the observed constancy of the rest-mass in the present era is also interpreted. 相似文献
15.
1 INTRODUCTIONIn theoretical physics, the thermodynamics of blajck holes remains an enigma, it turns outto be a junction of general relativity) quantum mechanics, and statistical physics.Since Bekenstein and Hawking proposed, in 1970s, that the black hole eatropy is proportional to the area of the event horizon (Bekenstein 1972, 1973, 1974; Hawking 1975; Kalloshet al. 1993), many efforts are devoted to the study of the statistical origin of the black holeentropy)One such effort is the wi… 相似文献
16.
Biman B. Nath 《Journal of Astrophysics and Astronomy》2011,32(4):545-548
The Intracluster Medium (ICM) is believed to have been affected by feedback from Active Galactic Nuclei (AGN) and/or supernovae-driven
winds. These sources are supposed to have injected entropy into the ICM gas. The recently determined universal pressure profile
of the ICM gas has been used and after comparing with the entropy profile of the gas from gravitational effects of the dark
matter halo, the additional entropy injected by non-gravitational sources, as a function of the total cluster mass is determined.
The current observational data of red-shift evolution of cluster scaling relation is shown that allow models in which the
entropy injection decreases at high red-shift. 相似文献
17.
Christopher Essex 《Planetary and Space Science》1984,32(8):1035-1043
Even though irreversible thermodynamics is meant to be a universal theory for nonequilibrium processes, that theory has not taken nonequilibrium radiation processes, which can normally be ignored, into account; thus it is primarily a theory for matter. When the simple bilinear entropy production rate of irreversible thermodynamics is modified, to account for the entropy production due to radiation while preserving local equilibrium for matter, the simple bilinear form of that rate, on which the current theory depends, is lost. Despite substantial compromises, generalized definitions for forces and fluxes cannot restore that simple homogeneous bilinear form, nor do they succeed in generating even generalized bilinearity in the entropy production rates for some problems concerning radiation. The possibility of a broader nonequilibrium theory is suggested by radiation problems, characterized by an example due to Planck, where those generalizations fail and the entropy production rate is a minimum in the steady state. 相似文献
18.
We study the effects of the generalized uncertainty principle in the tunneling formalism for Hawking radiation to evaluate the quantum-corrected Hawking temperature and entropy for a Kerr black hole. By assumption of a spatially flat universe accompanied with expansion of metric, the modified area and entropy of Kerr black hole are calculated and we could obtain an expression for entropy of black hole that is changing with respect to time and Bekenstein-Hawking temperature. 相似文献
19.
D. Gerbal H.V. Capelato F. Durret G.B. Lima Neto I. Márquez 《Astrophysics and Space Science》2001,276(2-4):861-868
We suggest that elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may have a specific entropy. We use
the Sérsic law to describe the light profile. The specific entropy (the Boltzmann–Gibbs definition) is then calculated assuming
that the galaxy behaves as a spherical, isotropic, one-component system. We predict a relation between the three parameters
of the Sérsic law linked to the specific entropy, defining a surface in the parameter space, an ‘entropic plane’. We have
analysed a sample of simulated merging elliptical galaxies (virtual) and a sample of galaxies belonging to the Coma Cluster (real). Both virtual and realgalaxies are: 1) located in their own ‘entropic plane‘ and 2) in this plane, they are located on a straight line, indicating
constant entropy: another physical property A careful examination of the value of the specific entropy indicates a very small
increase in the specific entropy with the generation after merging (virtual sample). Although one cannot distinguish between various generations for real galaxies, the distribution of specific entropy in this sample is very similar to that in the virtual sample.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
《天文和天体物理学研究(英文版)》2016,(2)
This paper is devoted to discussing the difference in the thermodynamic entropy budget per baryon in each type of stellar object found in the Universe. We track and discuss the actual decrease of the stored baryonic thermodynamic entropy from the most primitive molecular cloud up to the final fate of matter in black holes, passing through evolved states of matter as found in white dwarfs and neutron stars.We then discuss the case of actual stars with different masses throughout their evolution, clarifying the role of the virial equilibrium condition for the decrease in entropy and related issues. Finally, we discuss the role of gravity in driving the composition and the structural changes of stars with different Main Sequence masses during their evolution up to the final product. Particularly, we discuss the entropy of a black hole in this context arguing that the dramatic increase in its entropy, differently from the other cases, is due to the gravitational field itself. 相似文献