Robertson-Walker-type universes with conformally-invariant scalar field

Recently, Innaiah and Reddy (1985) obtained a flat Robertson-Walker-type solution for the Einstein field equations with the trace-free energy-momentum tensor of a conformally invariant scalar field as source. Here we show that the field equations force the scalar field to be independent of time. Furthermore, we obtain open and closed Robertson-Walker-type solutions and observe that, once again, the scalar field has to be independent of time.     

Robertson-walker type Lyttleton-Bondi universe

The exterior field of the Robertson-Walker type metric in the Lyttleton-Bondi universe is considered and an exact solution is obtained. Some physical properties of the solution are discussed.     

Bianchi type-V Lyttleton-Bondi universe

The exterior field of the Bianchi type-V metric in the Lyttleton-Bondi universe is considered. It is shown that the Bianchi type-V Lyttleton-Bondi universe, under certain conditions, does not exist.     

Bianchi type-I Lyttleton-Bondi universe

We present a scalar-tensor theory whose weak field limit gives exactly the potential proposed by Fischbachet al. (1986). The three experimental constantsG , , and are related to three parameters in our theory. At the level of the theory we have obtained the field produced by a source. The way this field should couple with a massive and charged particle (baryonic hypercharge) is a matter beyond the scope of this work.     

Robertson-Walker Lyttleton-Bondi universe with cosmological constant

It is shown that contortion and gravity are not interacting in the lowest possible order. The most convenient pairs of materials in the new Eötvös' experiments are also proposed.     

Exact Bianchi type-II Lyttleton-Bondi universe

The exterior field of the Bianchi type-II metric in the Lyttleton-Bondi universe is considered and an exact cosmological model is presented. The behaviour of the model is also discussed.     

Exact Bianchi type-II Lyttleton-Bondi universe

The exterior field of the Biachi type-II metric in the Lyttleton-Bondi universe is considered and an exact cosmological model is presented. The behaviour of the model is also discussed.     

Open and closed magnetospheric tail configurations and their stability

The asymptotic theory valid for magnetospheric tail configurations that vary only weakly in the antisolar direction is used to derive a number of explicit properties. The conditions under which the magnetopause converges to form a closed magnetosphere or diverges (open magnetosphere) are identified and discussed. It is shown that the presence of the high latitude low pressure tail lobes guarantees the open solution. The large value of the Mach-number of the unperturbed solar wind is the reason for the slow variation of the plasma and field quantities along the tail. Criteria for (two-dimensional) stability are discussed and it is shown that they can be expressed in terms of simple topological properties of the equilibria. Closed magnetopheres turn out to be stable, open magnetospheres with sufficiently stretched field lines are subject to an instability which — as shown earlier —may be the cause of magnetospheric substorms.     

Two universes

The community of astrophysicists see the universe in two different ways. Most of them believe that the evidence points to a hot big bang universe. The minority, largely represented at this meeting, believe that if proper weight is given to all of the observational evidence, rather than only a part of it, a very different model of the universe is indicated. Here I summarize that part of the evidence ignored by the majority, which shows (a) that not all redshifts are due to expansion, and (b) that galaxies and other coherent objects probably did not form from the condensation of diffuse gas.     

Bianchi type-III model in the Lyttleton-Bondi universe

The exterior field of the Bianchi type-III metric in the Lyttleton-Bondi universe is considered and an exact cosmological model is presented. Some physical properties of the model are discussed.     

Twin universes cosmology

Starting from the field equationS =(T -A(T)), presented in a former paper, we present a test result, based on numerical simulations, giving a new model applied to the very large structure of the Universe. A theory of inverse gravitational lensing is developed, in which the observed effects could be due mainly to the action of surrounding antipodal matter. This is an alternative to the explanation based on dark matter existence. We then develop a cosmological model. Because of the hypothesis of homogeneity, the metric must be a solution of the equationS = 0, although the total mass of the Universe is non-zero. In order to avoid the trivial solutionR = constant ×t, we consider a model with variable constants. Then we derive the laws linking the different constants of physics:G, c, h, m; in order to keep the basic equations of physics invariant, so that the variation of these constants is not measurable in the laboratory, the only effect of this process being the red shift, due to the secular variation of these constants. All the energies are conserved, but not the masses. We find that all of the characteristic lengths (Schwarzschild, Jeans, Compton, Planck) vary like the characteristic lengthR, from where all the characteristic times vary like the cosmic timet. As the energy of the photonh is conserved over its flight, the decrease of its frequency is due to the growth of the Planck constanth t. In such conditions the field equations have a single solution, corresponding to a negative curvature and to an evolution law:R t ^2/3.The model is no longer isentropic ands logt. The cosmologic horizon varies likeR, so that the homogeneity of the Universe is ensured at any time which constitues an alternative to the theory of inflation. We re-find, for moderate distances, Hubble's law. A new law: distance =f(z) is derived, very close to the classical one for moderate red shifts.     

Electromagnetic rotating universes

We study the Einstein-Maxwell equations for a tilted Bianchi type-II space-time. The matter content is a perfect fluid, with equation of statep=(γ?1)ε, (1≤γ≤2). The field equations are solved for all values of γ in the limiting case of small vorticity. The source of rotation is an electromagnetic field, which from observational requirements must be a small quantity at the present time.     

Bianchi type-II string-dust universes

We present an exact solution of Einstein's equations for cosmological models of Bianchi type-II filled with string dust as the source for the gravitational field. The solution represents an expanding and anisotropic universe which would give essentially an empty universe for large time. Some kinematical properties of the solution are discussed.     

Bianchi type-VI0 model in the Lyttleton-Bondi universe

The exterior field of the Bianchi type-VI₀ metric in the Lyttleton-Bondi universe is considered and an exact cosmological model is presented. Some physical properties of the model are discussed.     

On old universes and galaxy evolution

It is assumed that the universe can be represented by low density Friedmann models with non-zero cosmological constant and long ages. By comparing theoretical and observational apparent magnitude-redshift relations, the rates of galaxy evolution required to force coincidence of these relations in visual light are deduced for each model. These rates are compared with various recent estimates of this effect and are also used to predict the slope of the bright end of the luminosity function of elliptical galaxies. Both the comparison and the prediction indicate that, unless the slope of the bright end of the luminosity function is considerably flatter than that produced by extrapolation, it is impossible to assign all of the difference between theory and present observations to evolutionary effects. Such an assignment could, however, be made if a dispersion in the luminosities of the most distant galaxies is found.     

Stable magnetic universes revisited

Recent discovery of magnetars (B～10¹⁵ G) motivates us to consider magnetic universes in general relativity a new. A regular class of static, cylindrically symmetric pure magnetic field metrics is rederived in a different metric ansatz in all dimensions. Radial, time dependent perturbations show that for dimensions d>3 such spacetimes are stable at both near r≈0 and large radius r→∞. For d=3, however, simultaneous stability requirement at both, near and far radial distances can not be reconciled for time-dependent perturbations. We argue that this distinct property may be the cause for the absence of pure magnetic black holes in d=3. Restricted, numerical geodesics for neutral particles reveal a gravitational confinement around the center in the polar plane. Charged, time-like geodesics for d=4 are shown numerically to remain confined as well.     

Robertson-Walker Lyttleton-Bondi universe with cosmological constant — A comment

It is shown that the exterior solutions of the Robertson-Walker metric in the Lyttleton-Bondi universe with cosmological constant are, in general, those space-times which represent stiff matter fluids in general relativity theory. This shows that a result stated by Varma and Roy is incorrect.     

Linearly expanding universes in JBD-theory

The assumption of a linearly expanding universe for the JBD-cosmological equations generates a set of solutions for the barotropic equations of statep= (=const.). These solutions turn out to be valid for closed space-except in the casep= which is for open space. The gravitational constant which is inversely proportional to the scalar field increases with time if >–1/3 and decreases for <–1/3. No solution exists for =1/3. The Brans-Dicke parameter is negative if <–1/3.     

Plane-symmetric universes in general relativity

Plane-symmetric solutions of Einstein's field equations in vacuum, in the presence of electromagnetic fields and with cosmological constant are explored in null coordinates. The gravitational field of an infinite plane (uncharged and charged both) is thus obtained in a simple and systematic way. The method adopted for these solutions has possibilities of generalization.     

Viscous universes without initial singularity

It is shown that within a certain class of cosmological models (homogeneity and isotropy, two-component non-interacting fluid, density-dependent coefficient of bulk viscosity) the introduction of bulk viscosity effectively removes the initial singularity.