Observational cosmology

2021 ◽  
pp. 398-416
Author(s):  
Andrew M. Steane
Keyword(s):  
Deceleration Parameter ◽  
Hubble Parameter ◽  
Statistical Error ◽  
Simple Calculation ◽  
Observational Cosmology ◽  
Spatial Curvature ◽  
Sky Surveys ◽  
Redshift Surveys ◽  
Accelerating Expansion ◽  
Age Estimates

The main strands of observation in cosmology are presented. These are redshift surveys using standard candles; galaxy distributions; age estimates drawing on a number of strands of evidence; and the CMB radiation. The chapter begins with a discussion of systemtic and statistical error in measurements, and explains the terminology of “Lambda CDM” model. Observations are combined with the Friedman equation in order to constrain the density parameters in a LCDM model. Data from supernova surveys are used to obtain the Hubble parameter and the deceleration parameter, and hence evidence of an accelerating expansion. Evidence of the BAO process is deduced from sky surveys, and used to constrain the spatial curvature. The CMB radiation is discussed at length. The Sachs-Wolfe effect is obtained by a simple calculation,. The method to deduce spatial curvature from the position of the acoustic peaks is outlined. Further features such as spectal index and polarization are briefly discussed.

scholarly journals Cosmological Information from Galaxies and Radio Galaxies

1972 ◽  
Vol 44 ◽  
pp. 314-340 ◽  
Author(s):  
J. V. Peach
Keyword(s):  
Deceleration Parameter ◽  
Hubble Parameter ◽  
Radio Galaxies ◽  
Local Anisotropy ◽  
Cluster Galaxies ◽  
Recent Developments

An account is given of recent developments in the derivation of the value of the Hubble parameter applicable to regions beyond the local anisotropy. Recent observations relevant to interpretations of the magnitude-redshift diagram for cluster galaxies are discussed, in an attempt to assess uncertainties in the value of the deceleration parameter.

scholarly journals Dark Matter in the Universe

1986 ◽  
Vol 7 ◽  
pp. 27-38 ◽  
Author(s):  
Vera C. Rubin
Keyword(s):  
Dark Matter ◽  
Deceleration Parameter ◽  
Big Bang ◽  
Theoretical Cosmology ◽  
Observational Cosmology ◽  
The Past ◽  
The Galaxy ◽  
Expansion Of The Universe ◽  
The Big Bang ◽  
The Universe

Thirty years ago, observational cosmology consisted of the search for two numbers: Ho, the rate of expansion of the universe at the position of the Galaxy; and qo, the deceleration parameter. Twenty years ago, the discovery of the relic radiation from the Big Bang produced another number, 3oK. But it is the past decade which has seen the enormous development in both observational and theoretical cosmology. The universe is known to be immeasurably richer and more varied than we had thought. There is growing acceptance of a universe in which most of the matter is not luminous. Nature has played a trick on astronomers, for we thought we were studying the universe. We now know that we were studying only the small fraction of it that is luminous. I suspect that this talk this evening is the first IAU Discourse devoted to something that astronomers cannot see at any wavelength: Dark Matter in the Universe.

scholarly journals LRS Bianchi type-I cosmological model with constant deceleration parameter in f(R,T) gravity

2017 ◽  
Vol 14 (11) ◽  
pp. 1750158 ◽  
Author(s):  
Binaya K. Bishi ◽  
S. K. J. Pacif ◽  
P. K. Sahoo ◽  
G. P. Singh
Keyword(s):  
Cosmological Model ◽  
Deceleration Parameter ◽  
Hubble Parameter ◽  
Bianchi Type ◽  
Specific Model ◽  
Type I ◽  
Hubble’S Parameter ◽  
Constant Deceleration Parameter ◽  
Bianchi Type I ◽  
Spatially Homogeneous

A spatially homogeneous anisotropic LRS Bianchi type-I cosmological model is studied in [Formula: see text] gravity with a special form of Hubble's parameter, which leads to constant deceleration parameter. The parameters involved in the considered form of Hubble parameter can be tuned to match, our models with the [Formula: see text]CDM model. With the present observed value of the deceleration parameter, we have discussed physical and kinematical properties of a specific model. Moreover, we have discussed the cosmological distances for our model.

scholarly journals Accelerated expansion of the universe from the perspective of inhomogeneous cosmology

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040037
Author(s):  
Irina Bormotova ◽  
Elena Kopteva ◽  
Mariia Churilova ◽  
Zdenek Stuchlik
Keyword(s):  
Deceleration Parameter ◽  
Spherical Symmetry ◽  
Accelerated Expansion ◽  
Spatial Curvature ◽  
Inhomogeneous Cosmology ◽  
Spatial Part ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Special Case ◽  
Universe Evolution

We present a special case of the Stephani solution with spherical symmetry while considering different values of spatial curvature. We investigate the dynamics of the universe evolution in our model, build the R–T-regions for the resulting spacetime and analyze the behavior of the deceleration parameter. The singularities of the model are also discussed. The geometry of the spatial part of the obtained solution is explored.

scholarly journals Quantum Cosmology vs. Observational Cosmology (A Simple, Curious and Advanced Approach)

2016 ◽  
Author(s):  
U. V. S. Seshavatharam ◽  
S. Lakshminarayana
Keyword(s):  
Energy Density ◽  
Kinetic Energy ◽  
Hubble Parameter ◽  
Quantum Cosmology ◽  
Mass Density ◽  
Critical Density ◽  
Observational Cosmology ◽  
Cosmic Expansion ◽  
Expansion Speed ◽  
The Future

With reference to Planck scale Hubble parameter, super luminal expansion speeds, super luminal rotation speeds and Mach’s principle, we review the current cosmological observations. With our revised assumptions, it is possible to show that, at H0 =70 km/sec/Mpc, current cosmic temperature, age, radius, mass, mass density and rotational kinetic energy are 2.721 K, 4.41 x 1017 sec, 90 billion light years, 1.14654 x 1054 kg, 0.0482 times the current critical density and 0.6667 times the current critical energy density respectively. Based on the estimated current mass density and current rotational kinetic energy density, current cosmic dark matter density can be shown to be 0.2851 times the current critical density. Initial and current expansion speeds are 3 x 108 m/sec and 3.56 x 109 m/sec respectively. Proceeding further, we developed two interesting methods for understanding cosmic scale factor with reference to a temperature of 3000 K, redshift of 1100 and age of 3,69,000 years. Finally we would like to suggest that, with increasing cosmic age and increasing cosmic expansion speed, current universe is expanding with a speed of 11.885c. Magnitude of the future cosmic expansion speed depends on the magnitude of the future Hubble parameter. By knowing the time to time future cosmic temperatures, corresponding future Hubble parameters can be estimated and corresponding future cosmic expansion speeds can also be estimated.Proceeding further, a unified model of evolving quantum cosmology can be developed.

Swampland criteria and cosmological behavior of Tsallis holographic dark energy in Bianchi -III Universe

2020 ◽  
Vol 17 (07) ◽  
pp. 2050098 ◽  
Author(s):  
Umesh Kumar Sharma ◽  
Shikha Srivastava ◽  
A. Beesham
Keyword(s):  
Dark Energy ◽  
Deceleration Parameter ◽  
Holographic Dark Energy ◽  
Accelerating Universe ◽  
Accelerating Expansion ◽  
Bianchi Iii ◽  
Expansion Of The Universe ◽  
Hubble Horizon ◽  
The Universe ◽  
Universe Evolution

In this paper, a new form of dark energy, known as Tsallis holographic dark energy (THDE), with IR cutoff as Hubble horizon proposed by Tavayef et al. Tsallis holographic dark energy, Phys. Lett. B 781 (2018) 195 has been explored in Bianchi-III model with the matter. By taking the time subordinate deceleration parameter, the solution of Einstein’s field equation is found. The Universe evolution from earlier decelerated to the current accelerated phase is exhibited by the deceleration parameter acquired in the THDE model. It can be seen that the derived THDE model is related to an accelerating Universe with quintessence ([Formula: see text]). The squared sound speed [Formula: see text] also suggests that the THDE model is classically stable at present. In addition, the quintessence phase of the THDE model is analyzed with swampland conjecture to reformulate the accelerating expansion of the Universe.

KALUZA–KLEIN COSMOLOGICAL MODELS WITH ANISOTROPIC DARK ENERGY

2011 ◽  
Vol 26 (10) ◽  
pp. 739-750 ◽  
Author(s):  
K. S. ADHAV ◽  
A. S. BANSOD ◽  
R. P. WANKHADE ◽  
H. G. AJMIRE
Keyword(s):  
Dark Energy ◽  
Exact Solutions ◽  
Deceleration Parameter ◽  
Hubble Parameter ◽  
Cosmological Models ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Anisotropic Dark Energy ◽  
The Law ◽  
Kaluza Klein

The exact solutions of the Einstein field equations for dark energy in Kaluza–Klein metric under the assumption on the anisotropy of the fluid are obtained by applying the law of variation of Hubble parameter which yields the constant value of deceleration parameter. The isotropy of the fluid, space and expansion are examined.

scholarly journals Tsallis holographic model of dark energy: Cosmic behavior, statefinder analysis and ωD–ωD′ pair in the nonflat universe

2019 ◽  
Vol 28 (15) ◽  
pp. 1950164 ◽  
Author(s):  
Vipin Chandra Dubey ◽  
Umesh Kumar Sharma ◽  
A. Beesham
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Holographic Dark Energy ◽  
Apparent Horizon ◽  
Density Parameter ◽  
Holographic Model ◽  
Spatial Curvature ◽  
Present Value ◽  
Evolutionary Trajectories

This paper investigates the Tsallis holographic dark energy (THDE) model in accordance with the apparent horizon as an infrared cut-off, in a non flat universe. The cosmological evolution of the deceleration parameter and equation of state of THDE model are calculated. The evolutionary trajectories are plotted for the THDE model for distinct values of the Tsallis parameter [Formula: see text] besides distinct spatial curvature contributions, in the statefinder [Formula: see text] parameter-pairs and [Formula: see text] plane, considering the present value of dark energy (DE) density parameter [Formula: see text], [Formula: see text], in the light of [Formula: see text] observational data. The statefinder and [Formula: see text] plane plots specify the feature of the THDE and demonstrate the separation between this framework and other models of DE.

scholarly journals Study of Homogeneous and Isotropic Universe in f(R,Tφ) Gravity

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
M. Sharif ◽  
Aisha Siddiqa
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Hubble Parameter ◽  
State Parameter ◽  
Universe Model ◽  
Effective Equation ◽  
Isotropic Universe ◽  
First Order ◽  
Equation Of State Parameter

This paper is devoted to study the cosmological behavior of homogeneous and isotropic universe model in the context of f(R,Tφ) gravity, where φ is the scalar field. For this purpose, we follow the first-order formalism defined by H=W(φ). We evaluate Hubble parameter, effective equation of state parameter (ωeff), deceleration parameter, and potential of scalar field for three different values of W(φ). We obtain phantom era in some cases for the early times. It is found that exponential expression of W(φ) yields ωeff independent of time for flat universe and independent of model parameter otherwise. It is concluded that our model corresponds to ΛCDM for both initial and late times.

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