Redshift evolution of angular diameters and surface brightness: how rigid are galactic measuring rods?

The effect of a cosmic time variation of Newton’s constant on galactic angular diameters, linear size, apparent magnitude, and surface brightness is investigated. The redshift scaling of the gravitational constant is proportional to the Hubble parameter, derived from the constancy of a moderate dimensionless ratio of fundamental constants, and manifested in galactic linear-size evolution. The latter is demonstrated by fitting the angular size–redshift relation to spectroscopically and photometrically selected samples of high-redshift rotators. The intrinsic luminosity evolution of the rotators and their magnitude–redshift and surface brightness–redshift relations are studied. The galactic luminosity scales with a power of the Hubble parameter, and the scaling exponent is inferred from a moderate dimensionless ratio involving the gravitational constant, the Galactic luminosity, and the velocity of the Galaxy in the microwave background. The fits are performed with a cosmic expansion factor derived from paleoplanetary surface temperatures. This expansion factor is tested by comparing the corresponding redshift evolution of the angular-size distance to the distance estimates of two samples of galaxy clusters.     

Ether, Luminosity and Galactic Source Counts

An interpretation of the cosmological redshift in terms of a cosmic ether is given. We study a Robertson-Walker cosmology in which the ether is phenomenologically defined by a homogeneous and isotropic permeability tensor. The speed of light becomes so a function of cosmic time like in a dielectric medium. However, the cosmic ether is dispersion free, it does not lead to a broadening of spectral lines. Locally, in Euclidean frames, the scale factors of the permeability tensor get absorbed in the fundamental constants. Mass and charge scale with cosmic time, and so do atomic energy levels. This substantially changes the interpretation of the cosmological redshift as a Doppler shift. Photon frequencies are independent of the expansion factor; their time scaling is determined by the permeability tensor. The impact of the ether on the luminosity-distance, on the distance-redshift relation, and on galactic number counts is discussed. The Hubble constant is related to the scale factors of the metric and the permeability tensor. We study the effects of the ether at first in comoving Robertson-Walker coordinates, and then, in the context of a flat but expanding space- time, in the globally geodesic rest frames of galactic observers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solutions to the field equations and the deceleration parameter

We utilise a form for the Hubble parameter to generate a number of solutions to the Einstein field equations with variable cosmological constant and variable gravitational constant. The Hubble law utilised yields a constant value for the deceleration parameter. A variety of solutions is presented in the Robertson-Walker spacetimes. A generalisation of the cosmic scale factor is utilised in the anisotropic Bianchi I spacetime to illustrate that new solutions may also be found in spacetimes with less symmetry than Robertson-Walker. We also show that the constant deceleration parameter used is consistent with alternate theories of gravity by considering the scalar-tensor theory of Lau and Prokhovnik with ak = 0 Robertson-Walker background.     

A cosmological model with both deceleration and acceleration

In this paper, we investigate a variation law for Hubble’s parameter in the curved, expanding background of spatially homogeneous, anisotropic Bianchi type I space-time. By choosing a particular form of the generalized Hubble’s parameter, which gives an early deceleration and late time acceleration for the anisotropic Bianchi type I cosmological model, we show that the model approaches isotropy and tends to a de Sitter universe at late times. The cosmological term asymptotically tends to a genuine cosmological constant and the solution is consistent with recent observations.     

The influence of gravitational binding energy on cosmic expansion dynamics: new perspectives for cosmology

Confronted with microwave background observations by WMAP and with consternating supernova locations in the magnitude–redshift diagram modern cosmology feels enforced to call for cosmic vacuum energy as a necessary cosmological ingredient. Most often this vacuum energy is associated with Einstein’s cosmological constant Λ or with so-called “dark energy”. A positive value of Λ describes an inflationary action on cosmic dynamics which in view of recent cosmological data appears as an absolute need. In this article, however, we question the hypothesis of a constant vacuum energy density since not justifiable on physical grounds. Instead we show that gravitational binding energy of cosmic matter, connected with ongoing structure formation during cosmic expansion, acts similar to vacuum energy, since it reduces the effective gravitating proper mass density. Thus one may be encouraged to believe that actions of cosmic vacuum energy and gravitational binding energy concerning their cosmological effects are closely related to each other, perhaps in some respects even have identical phenomenologies.     

On the Hubble Law in a Nonexpanding Nonstationary Universe with Cosmological Constant

A nonsingular, homogeneous, isotropic cosmological model with cosmological constant in flat space-time theory of gravitation is studied. The second law of thermodynamics yields a nonexpanding (nonstationary) universe without entropy production. At the beginning of the universe radiation, matter and vacuum energy given by the cosmological constant are zero and then emerge from gravitational energy. In the course of time the energy of radiation and matter decrease whereas the vacuum energy increases forever. Light emitted from a distant galaxy loses energy on his way to the observer producing the observed redshift. The velocity of light in the past is greater than the present one. This may explain superluminal velocities but only for large redshifts. The sum of the density parameters of matter, radiation and vacuum energy is a little greater than one. All the matter can be baryonic. There is no age problem of the universe. This revised version was published online in July 2006 with corrections to the Cover Date.     

General class of Bianchi cosmological models with Λ in creation-field cosmology

The solutions of Einstein’s equations with cosmological constant (Λ) in the presence of a creation field have been obtained for general class of anisotropic cosmological models. We have obtained the cosmological solutions for two different scenarios of average scale factor. In first case, we have discussed three different types of physically viable cosmological solutions of average scale factor for the general class of Bianchi cosmological models by using a special law for deceleration parameter which is linear in time with a negative slope. In second case, we have discussed another three different forms of cosmological solutions by using the average scale factor in three different scenarios like Intermediate scenario, Logamediate scenario and Emergent scenario. All physical parameters are calculated and discussed in each physical viable cosmological model. We examine the nature of creation field and cosmological constant is dominated the early Universe but they do not survive for long time and finally tends to zero for large cosmic time t. We have also discussed the all energy conditions in each cases.     

A comparative study of Brans-Dicke and general relativistic cosmologies in terms of observationally measurable quantities

A comparison between general relativistic and Brans-Dicke cosmologies is made in terms of quantities measurable by an observational astronomer. Numerical integration of the Brans-Dicke field equations was employed to find the relationships of the mean density of cosmic matter, the age, and the time derivative of the gravitational constant to the Hubble constant and deceleration parameter. The difference between general relativistic and Brans-Dicke apparent magnitude-redshift diagrams was found to be negligible even at large redshifts under the assumption of no galactic evolution in absolute magnitude.     

Relativistic Cosmology with Zero Deceleration Parameter

The possibility that the deceleration parameter q might be a null constant is discussed; such possibilitiy is interesting because solves the horizon problem and the flatness problem with no need of inflation. A simple way to get q = const = 0 is explored: the way assumes Einstein's field equations without cosmological term and introduces a massless scalar field V with negative energy density. Both in the early and in the present universe one finds the Whitrow-Randall relation Gut² = const 1 G gravitational coupling, u mass-energy density, t cosmic time). The interaction between the V-field and the ordinary matter is briefly discussed; as possible consequence of this interaction the true value of the Hubble parameter might be one half the observed value. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some Robertson-Walker models with time dependent <Emphasis Type="Italic">G</Emphasis> and Λ

Einstein field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for Robertson-Walker universe by assuming the cosmological term proportional to the Hubble parameter. This variation law for vacuum density has recently been proposed by Schützhold on the basis of quantum field estimations in the curved and expanding background. The cosmological term tends asymptotically to a genuine cosmological constant and the model tends to a deSitter universe. We obtain that the present universe is accelerating with a large fraction of cosmological density in the form of cosmological term.     

Empirical Status in Cosmology and the Problem of the Nature of Redshifts

When comparing the results of the cosmological tests obtained by various authors using various methods, it is found that there has not been any trend of convergence in the values obtained for the deceleration parameter q₀, in spite of the accumulated and more accurate data. The empirical data – those on the global and the local cosmological tests and those pointing to the non-existence of cosmic evolutionary effects – can be interpreted in a plausible way in the framework of a static EUCLID ean model. This well reconciles the non-DOPPLER ian nature of redshifts implied by the studies of the redshift phenomenon itself.     

Cosmology without Big Bang for the whole time scale (repulsion era and attraction era)

In several papers the 5‐dimensional Projective Unified Field Theory (PUFT) of the author (Schmutzer 1998, Schmutzer 1999, Schmutzer 2000a) was applied to a homogeneous, isotropic and closed cosmological model without pressure (cosmology of the attraction era). Here we derive a cosmological equation of state for the pressure. This step enables us to treat cosmology for the complete time scale from the big start (Urstart) to the present time (repulsion era and attraction era). Here following subjects are treated, where our specific terminology of PUFT is taken over from our previous publications quoted above: cosmological equation of state for the pressure, numerical integration of the system of the resulting cosmological differential equations and evaluation of the results. Specific outcomes (temporal course and present values) are given for the following cosmological quantities: radius and age of the world, cosmological frequency shift (Hubble factor), deceleration parameter, effective gravitational “constant”, mass density, temperature, pressure, entropy, behavior of the photon gas and of the mechanical particle gas etc.     

Bianchi type I two-fluid cosmological models with a variable G and Λ

This paper presents anisotropic, homogeneous two-fluid cosmological models in a Bianchi type I space–time with a variable gravitational constant G and cosmological constant Λ. In the two-fluid model, one fluid represents the matter content of the universe and another fluid is chosen to model the CMB radiation. We find a variety of solutions in which the cosmological parameter varies inversely with time t. We also discuss in detail the behavior of associated fluid parameters and kinematical parameters. This paper pictures cosmic history when the radiation and matter content of the universe are in an interactive phase. Here, Ω is closing to 1 throughout the cosmic evolution.      

Universe's Expansion Puts Limits On The Cosmic Time ScaleVariations Of Gravitational And Cosmological `Constants'

Limits on cosmic time scale variations of gravitational and cosmological `constants' are studied. The study is based on a function which can measure the temporal variation of the magnitude of the gradient of any scalar field defined inside a medium exposed to a gravitational field. The cosmic time dependent scalar fields are taken to be the gravitational and cosmological `constants'. The medium; in which those scalar fields are defined; is taken to be the spatially perturbed Friedman-Robertson-Walker (FRW) expanding universe. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kaluza-Klein radiating model in a general scalar-tensor theory

A five dimensional Kaluza-Klein space-time is considered in the presence of prefect fluid source in the general scalar-tensor theory of gravitation proposed by Nordtvedt (Astrophys. J. 161:1069, 1970) with the help of special law of variation for Hubble’s parameter given by Bermann (Nuovo Cimento 74B:182, 1983). A cosmological model with a negative constant deceleration parameter is obtained in this theory. Some physical properties of the model are also discussed.     

Viscous fluid cosmology with a cosmological constant

Exact solutions of the field equations for a Bianchi type-I space-time, filled with a viscous fluid and cosmological constant, are obtained. We utilize the constancy of deceleration parameter to get singular and non-singular solutions. We investigate a number of solutions with constant and time-varying cosmological constant together with a linear relation between shear viscosity and expansion scalar. Due to dissipative processes, the mean anisotropy and shear of the model tend to zero at a faster rate.     

Bianchi type-I cosmological models with time dependent G and Λ

Einstein field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for Bianchi type-I universe by assuming the cosmological term proportional to the Hubble parameter. This variation law for vacuum density has recently been proposed by Schützhold on the basis of quantum field estimations in the curved and expanding background. The model obtained approaches isotropy. The cosmological term tends asymptotically to a genuine cosmological constant, and the model tends to a deSitter universe. We obtain that the present universe is accelerating with a large fraction of cosmological density in the form of cosmological term.     

Can redshift discrepancies in galaxy systems be explained by low-frequency gravitational radiation? I. distant clusters

Some proposals have been made in recent years that extremely low-frequency cosmic gravitational radiation with wavelengths of the order megaparsecs and larger and with the cosmological energy density may be able to explain the virial mass discrepancy in at least some systems of galaxies. The question is rediscussed here with the result that — for all conceivable spectral densities — the gravitational wave influence on the propagation of light from a galaxy cluster does not solve redshift problem for rich and distant clusters — at least if waves with an energy density not exceeding the critical cosmological density are considered.     

Distance measurements as a probe of cosmic acceleration

A major recent development in observational cosmology has been an accurate measurement of the luminosity distance–redshift relation out to redshifts z =0.8 from Type Ia supernova standard candles. The results have been argued as evidence for cosmic acceleration. It is well known that this assertion depends on the assumption that we know the equation of state for all mass–energy other than normal pressureless matter; popular models are based either on the cosmological constant or on the more general quintessence formulation. However, this assertion also depends on a number of other assumptions, implicit in the derivation of the standard cosmological field equations: large-scale isotropy and homogeneity, the flatness of the Universe, and the validity of general relativity on cosmological scales (where it has not been tested). A detailed examination of the effects of these assumptions on the interplay between the luminosity distance–redshift relation and the acceleration of the Universe is not possible unless one can define the precise nature of the failure of any particular assumption. However a simple quantitative investigation is possible and reveals a number of considerations about the relative importance of the different assumptions. In this paper we present such an investigation. We find that the relationship between the distant-redshift relation and the sign of the deceleration parameter is fairly robust and is unaffected if only one of the assumptions that we investigate is invalid so long as the deceleration parameter is not close to zero (it would not be close to zero in the currently favoured Ω_Λ=1−Ω_matter=0.7 or 0.8 Universe, for example). Failures of two or more assumptions in concordance may have stronger effects.