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Showing papers on "Deceleration parameter published in 1993"


Journal ArticleDOI
01 Jan 1993-Nature
TL;DR: In this paper, it was shown that very-long-baseline interferometry (VLBI) measurements of radio sources associated with active galaxies and quasars may be largely free of evolutionary effects even at substantial redshifts.
Abstract: IN cosmological models based on the standard Friedmann–Robertson–Walker geometry, the apparent flux density or angular size of standard candles or standard rods varies with redshift in a way that depends on the deceleration parameter q0. (Open universes have q0 0.5.) At low redshift, however, observational errors are much greater than the differences in q0 expected for different cosmological models, while at high redshift observational uncertainties, particularly at optical wavelengths, and apparent systematic evolutionary changes in sources obscure the expected geometrical effects. Here I show that measurements by very-long-baseline interferometry (VLBI) of compact radio sources associated with active galaxies and quasars may be largely free of evolutionary effects even at substantial redshifts. The relation between angular size and redshift for a sample of these sources indicates a value of q0 close to 0.5, corresponding to cosmological density near the critical value.

157 citations


Journal ArticleDOI
TL;DR: In this paper, a form for the Hubble parameter was used to generate a number of solutions to the Einstein field equations with variable cosmological constant and variable gravitational constant, which is consistent with alternate theories of gravity by considering the scalar-tensor theory of Lau and Prokhovnik with a 0 Robertson-Walker background.
Abstract: 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.

47 citations


Journal ArticleDOI
TL;DR: In this article, the authors show how to measure cosmological parameters using observations of inspiraling binary neutron star or black hole systems in one or more LIGO-like detectors.
Abstract: We show how to measure cosmological parameters using observations of inspiraling binary neutron star or black hole systems in one or more gravitational wave detectors. To illustrate, we focus on the case of fixed mass binary systems observed in a single Laser Interferometer Gravitational-wave Observatory (LIGO)-like detector. Using realistic detector noise estimates, we characterize the rate of detections as a function of a threshold signal-to-noise ratio $\rho_0$, the Hubble constant $H_0$, and the binary ``chirp'' mass. For $\rho_0 = 8$, $H_0 = 100$ km/s/Mpc, and $1.4 \msun$ neutron star binaries, the sample has a median redshift of $0.22$. Under the same assumptions but independent of $H_0$, a conservative rate density of coalescing binaries ($8\times10^{-8}\,{\rm yr}^{-1}\,{\rm Mpc}^{-3}$) implies LIGO will observe $\sim 50\,{\rm yr}^{-1}$ binary inspiral events. The precision with which $H_0$ and the deceleration parameter $q_0$ may be determined depends on the number of observed inspirals. For fixed mass binary systems, $\sim 100$ observations with $\rho_0 = 10$ in the LIGO detector will give $H_0$ to 10\% in an Einstein-DeSitter cosmology, and 3000 will give $q_0$ to 20\%. For the conservative rate density of coalescing binaries, 100 detections with $\rho_0 = 10$ will require about 4~yrs.

10 citations


Journal ArticleDOI
TL;DR: In this article, the flatness problem posed by Dicke is studied within the framework of the pulsating model and it is shown that Ω is a U-shaped function of the epoch: Ω = ∞ at the bounce as well as at the recollapse point.
Abstract: The flatness problem posed by Dicke is studied within the framework of the pulsating model. In contrast with the simple solution proposed by the inflationary models of Guth and others,i.e. Ω = 1 always, it is found that Ω is a U-shaped function of the epoch: Ω = ∞ at the bounce as well as at the recollapse point, and has a minimum, which may be close to but exceeding unity, that occursafter the expansion rate a has reached a maximum. The values of Ω, the deceleration parameter, the Hubble constant, and the look-back time for several key values of the expansion epoch are given in closed form. Importantly, in contrast with the standard model, forq = 1/2, one has Ω > 1. It is proposed that the reason why the Universe is apparently near the Ω-minimum at an epoch at which terrestrial science has developed to a point it can make such a determination is because there are relations between the parameters governing the cosmological-expansion and terrestrial-evolution rates, which generate this synchronism. There are two appendices: the first shows in detail that there is no particle horizon problem for the pulsating Universe, and the second presents a space-time imbedding argument which clarifies how the expansion rate a can exceed the numerical speed of light because it is analogous to a Minkowski proper velocity.

9 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that cosmological models with a constant deceleration parameter in general relativity without assuming a specific equation of state are equivalent to those with bulk viscosity.
Abstract: Recently Berman and Gomide have presented cosmological models with a constant deceleration parameter in general relativity without assuming a specific equation of state. It is shown that these models are equivalent to those with bulk viscosity. Some general remarks are made on the former models, including implications for violations of causality.

8 citations


Journal ArticleDOI
TL;DR: In this article, the age of the universe has been estimated to be 16±2 Gyr and an upper limit to the Hubble constant of 68 km s −1 Mpc −1.
Abstract: Colors of elliptical galaxies in nine distant clusters (z≤0.5) are studied with reference to theoretical models for evolutionary population synthesis (Buzzoni 1989) inferring allowed ranges for the relevant cosmological parameters. Galaxies at z=0.2 are found to be coeval within ±3 Gyr and consistent with an absolute age of 12 Gyr. The look-back time from z=0.2 to z=0.45 is not larger than 4 Gyr. In a Fiedmann cosmology this leads to a current age of the universe of 16±2 Gyr and an upper limit to the Hubble constant of 68 km s −1 Mpc −1 . The value of H 0 =52±2 recently suggested by Sandage and Tammann is supported by the data. In this case the deceleration parameter is found to be q 0 =0.06 -0.06 +0.14

4 citations


Journal ArticleDOI
TL;DR: In this paper, the consequences of the energy tensor of the polarized vacuum of quantum field theory implies the existence of a non-zero cosmological A term in i Einstein's gravitational equation.
Abstract: According to Zel’dovich, the energy tensor of the polarized vacuum of quantum field theory implies the existence of a non-zero cosmological A term in i Einstein’s gravitational equation. I investigate the consequences of Zel’dovich’s λ in a spatially flat isotropic universe with the Hubble parameterH proportional tot−1 (t = the cosmic time); I find:tH > 2/3, -1

1 citations


Journal ArticleDOI
TL;DR: The Bianchi-type cosmological models have been studied in Lyra's geometry for a law of variation of Hubble's parameter presented by Berman (1983) that yields constant deceleration parameter models of the universe.
Abstract: The Bianchi-type cosmological models have been studied in Lyra’s geometry for a law of variation of Hubble’s parameter presented by Berman (1983) that yields constant deceleration parameter models of the universe. All the models have a singular origin (t = 0) and evolve with time. The gauge function \(t) is an arbitrary function of time.

1 citations


Journal ArticleDOI
TL;DR: In this article, the Weinberg relation is explained based on the Zel'dovich energy tensor of vacuum in a Robertson-Walker universe with constant deceleration parameter, q = const.
Abstract: The Weinberg relation (which connects the Hubble constantH to the mass of a typical elementary particle) is an empirical relation hitherto unexplained. I suggest an explanation based on the Zel'dovich energy tensor of vacuum in a Robertson-Walker universe with constant deceleration parameter,q = const. This model leads to (a) the Weinberg relation, (b) a varying cosmological term Λ scaling asH2, (c) a varying gravitational constantG scaling asH, (d) a matter creation process throughout the universe at the rate 10−47 g s−1 cm3, (e) a deceleration parameter in the range -1 to 1/2, which allows a horizon-free universe and makes the lawG/H = constant, consistent with the Viking lander data on the orbit of planet Mars.