scholarly journals COSMOLOGICAL MODELS GENERALIZING ROBERTSON–WALKER MODELS

2003 ◽  
Vol 12 (09) ◽  
pp. 1603-1613
Author(s):  
ABDUSSATTAR
Keyword(s):  
Space Time ◽  
Cosmological Models ◽  
Einstein’S Field Equations ◽  
Field Equations ◽  
Einstein's Field Equations ◽  
The Universe

Considering the physical 3-space t= constant of the space–time metrics as spheroidal and pseudo-spheroidal, cosmological models which are generalizations of Robertson–Walker models are obtained. Specific forms of these general models as solutions of Einstein's field equations are also discussed in the radiation and the matter dominated era of the universe.

scholarly journals On eddington's problem of the expansion of the universe by condensation

1933 ◽  
Vol 140 (841) ◽  
pp. 269-276
Keyword(s):  
Equilibrium State ◽  
Static Condition ◽  
Einstein’S Field Equations ◽  
Field Equations ◽  
Einstein Universe ◽  
Einstein's Field Equations ◽  
Present Universe ◽  
Expansion Of The Universe ◽  
Static Einstein Universe ◽  
The Universe

1.The discovery of the general receding motion of the spiral nebulae by Hubble lent importance to the Friedmann-Lemaître solution of Einstein’s field equations and it was promptly suggested that our present universe started from a static condition, and owing to certain unknown causes began expanding and has since been doing so continuously. Eddington* pointed out that the static Einstein universe was unstable and so “exploded” (as Eddington put it) in some past age. Eddington suggested that the reason for explosion was the condensation of matter into stellar bodies out of the nebular mass uniformly filling up the Einstein universe. McCrea† and McVittie, working on this idea, proposed a proof showing that for a single condensation the universe would start contracting, but for more condensations start expanding from the equilibrium state. This proof they have recently withdrawn as being erroneous. Meanwhile, Lemaître§ himself enunciated a theorem stating that condensation itself could not cause expansion or contraction, but it was the stagnation of energy (ultimately amounting to condensation) which disturbed the equilibrium and caused the universe to swell up, but McCrea and McVittie showed that his proof was incorrect. Eddington’s problem thus remains where it was when first proposed. In this note we give a proof which shows that condensations, no matter whatever be their number, would start expansion of the Einstein universe.

Expanding Universe with a Variable Cosmological Term

2015 ◽  
Vol 70 (11) ◽  
pp. 905-911 ◽  
Author(s):  
Carlos Blanco-Pérez ◽  
Antonio Fernández-Guerrero
Keyword(s):  
Cosmological Constant ◽  
Cosmological Term ◽  
Expanding Universe ◽  
Einstein’S Field Equations ◽  
Field Equations ◽  
Variable Cosmological Term ◽  
Einstein's Field Equations ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Entropy Of The Universe

AbstractWe propose a model of expansion of the universe in which a minimal, ‘quantised’ rate is dependent upon the value of the cosmological constant Λ in Einstein’s field equations, itself not a constant but a function of the size and the entropy of the universe. From this perspective, we offer an expression which relates Hubble’s constant with the cosmological constant.

scholarly journals STRANGE QUARK MATTER ATTACHED TO THE STRING CLOUD IN THE SPHERICAL SYMMETRIC SPACE–TIME ADMITTING CONFORMAL MOTION

2005 ◽  
Vol 14 (08) ◽  
pp. 1365-1372 ◽  
Author(s):  
İLHAMİ YAVUZ ◽  
İHSAN YILMAZ ◽  
HÜSNÜ BAYSAL
Keyword(s):  
Symmetric Space ◽  
Quark Matter ◽  
Strange Quark ◽  
Space Time ◽  
Strange Quark Matter ◽  
Einstein’S Field Equations ◽  
Field Equations ◽  
Parameter Group ◽  
Conformal Motion ◽  
Einstein's Field Equations

In this paper, we have examined charged strange quark matter attached to the string cloud in the spherical symmetric space–time admitting one-parameter group of conformal motions. For this purpose, we have solved Einstein's field equations for spherical symmetric space–time with strange quark matter attached to the string cloud via conformal motions. Also, we have discussed the features of the obtained solutions.

scholarly journals ON SIGNATURE TRANSITION IN ROBERTSON–WALKER COSMOLOGIES

2000 ◽  
Vol 15 (10) ◽  
pp. 1521-1531 ◽  
Author(s):  
K. GHAFOORI-TABRIZI ◽  
S. S. GOUSHEH ◽  
H. R. SEPANGI
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Upper Bound ◽  
Classical Model ◽  
Space Time ◽  
Scale Factor ◽  
Einstein’S Field Equations ◽  
Field Equations ◽  
Lorentzian Space ◽  
Einstein's Field Equations

We analyze a classical model of gravitation coupled to a self-interacting scalar field. We show that, within the context of this model for Robertson–Walker cosmologies, there exist solutions in the spatially non-flat cases exhibiting transitions from a Euclidean to a Lorentzian space–time. We then discuss the conditions under which these signature changing solutions to Einstein's field equations exist. In particular, we find that an upper bound for the cosmological constant exists and that close to the signature changing hypersurface, both the scale factor and the scalar field have to be constant. Moreover we find that the signature changing solutions do not exist when the scalar field is massless.

scholarly journals Axially Symmetric Bulk Viscous String Cosmological Models in GR and Brans-Dicke Theory of Gravitation

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
V. U. M. Rao ◽  
D. Neelima
Keyword(s):  
General Relativity ◽  
Bulk Viscosity ◽  
Space Time ◽  
Cosmological Models ◽  
Axially Symmetric ◽  
Matter Distribution ◽  
Field Equations ◽  
Theory Of Gravitation ◽  
The Universe ◽  
Special Case

Axially symmetric string cosmological models with bulk viscosity in Brans-Dicke (1961) and general relativity (GR) have been studied. The field equations have been solved by using the anisotropy feature of the universe in the axially symmetric space-time. Some important features of the models, thus obtained, have been discussed. We noticed that the presence of scalar field does not affect the geometry of the space-time but changes the matter distribution, and as a special case, it is always possible to obtain axially symmetric string cosmological model with bulk viscosity in general relativity.

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