scholarly journals The background Friedmannian Hubble constant in relativistic inhomogeneous cosmology and the age of the Universe

2017 ◽  
Vol 598 ◽  
pp. A111 ◽  
Author(s):  
Boudewijn F. Roukema ◽  
Pierre Mourier ◽  
Thomas Buchert ◽  
Jan J. Ostrowski
Keyword(s):  
Energy Parameter ◽  
Hubble Constant ◽  
Expansion Rate ◽  
De Sitter ◽  
Low Mass Stars ◽  
Inhomogeneous Cosmology ◽  
Cosmological Time ◽  
Low Mass ◽  
Age Of The Universe ◽  
The Universe

Context. In relativistic inhomogeneous cosmology, structure formation couples to average cosmological expansion. A conservative approach to modelling this assumes an Einstein-de Sitter model (EdS) at early times and extrapolates this forward in cosmological time as a “background model” against which average properties of today’s Universe can be measured. Aims. This modelling requires adopting an early-epoch-normalised background Hubble constant Hbg1. Methods. Here, we show that the ΛCDM model can be used as an observational proxy to estimate Hbg1 rather than choose it arbitrarily. We assume (i) an EdS model at early times; (ii) a zero dark energy parameter; (iii) bi-domain scalar averaging-division of the spatial sections into over- and underdense regions; and (iv) virialisation (stable clustering) of collapsed regions. Results. We find Hbg1= 37.7 ± 0.4 km s-1/ Mpc (random error only) based on a Planck ΛCDM observational proxy. Conclusions. Moreover, since the scalar-averaged expansion rate is expected to exceed the (extrapolated) background expansion rate, the expected age of the Universe should be much younger than 2/(3Hbg1) = 17.3 Gyr. The maximum stellar age of Galactic bulge microlensed low-mass stars (most likely: 14.7 Gyr; 68% confidence: 14.0–15.0 Gyr) suggests an age of about a Gyr older than the (no-backreaction) ΛCDM estimate.

scholarly journals The Hubble Constant

2000 ◽  
Vol 17 (1) ◽  
pp. 45-47 ◽  
Author(s):  
Jeremy Mould
Keyword(s):  
Globular Clusters ◽  
Hubble Space Telescope ◽  
Hubble Constant ◽  
Big Bang ◽  
Accelerating Universe ◽  
De Sitter ◽  
Age Of The Universe ◽  
Extragalactic Distance Scale ◽  
The Big Bang ◽  
The Universe

AbstractWith the completion of the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale, it is interesting to form the dimensionless quantity H0t0 by multiplying the Hubble Constant by the age of the Universe. In a matter dominated decelerating Universe with a density exceeding 0·26 of the critical value, H0t0 < 1; in an accelerating Universe with the same Ωm = 0·26, but dominated by vacuum energy with ΩV ≥ 1 – Ωm, H0t0 ≥ 1. If the first globular clusters formed 109 years after the Big Bang, then with 95% confidence H0t0 =1·0 ± 0·3. The classical Einstein–de Sitter cosmological model has H0t0 = ⅔.

scholarly journals COSMOLOGICAL CONSTRAINTS FOR THE COSMIC DEFECT THEORY

2011 ◽  
Vol 20 (06) ◽  
pp. 1039-1051 ◽  
Author(s):  
NINFA RADICELLA ◽  
MAURO SERENO ◽  
ANGELO TARTAGLIA
Keyword(s):  
Large Scale ◽  
Hubble Constant ◽  
Big Bang ◽  
Nuclear Species ◽  
Type Ia ◽  
Species Abundances ◽  
Age Of The Universe ◽  
Ia Supernovae ◽  
The Big Bang ◽  
The Universe

The cosmic defect theory has been confronted with four observational constraints: primordial nuclear species abundances emerging from the big bang nucleosynthesis; large scale structure formation in the Universe; cosmic microwave background acoustic scale; luminosity distances of type Ia supernovae. The test has been based on a statistical analysis of the a posteriori probabilities for three parameters of the theory. The result has been quite satisfactory and such that the performance of the theory is not distinguishable from that of the ΛCDM theory. The use of the optimal values of the parameters for the calculation of the Hubble constant and the age of the Universe confirms the compatibility of the cosmic defect approach with observations.

scholarly journals Variation of the fundamental constants over the cosmological time: veracity of Dirac’s intriguing hypothesis

2016 ◽  
Vol 94 (1) ◽  
pp. 89-94 ◽  
Author(s):  
Cláudio Nassif ◽  
A.C. Amaro de Faria
Keyword(s):  
Fine Structure ◽  
Early Universe ◽  
Early Period ◽  
Planck Scale ◽  
Structure Constant ◽  
Energy Scale ◽  
Fine Structure Constant ◽  
Cosmological Time ◽  
Age Of The Universe ◽  
The Universe

We investigate how the universal constants, including the fine structure constant, have varied since the early universe close to the Planck energy scale (EP ∼ 1019 GeV) and, thus, how they have evolved over the cosmological time related to the temperature of the expanding universe. According to a previous paper (Nassif and Amaro de Faria, Jr. Phys. Rev. D, 86, 027703 (2012). doi:10.1103/PhysRevD.86.027703), we have shown that the speed of light was much higher close to the Planck scale. In the present work, we will go further, first by showing that both the Planck constant and the electron charge were also too large in the early universe. However, we conclude that the fine structure constant (α ≅ 1/137) has remained invariant with the age and temperature of the universe, which is in agreement with laboratory tests and some observational data. Furthermore, we will obtain the divergence of the electron (or proton) mass and also the gravitational constant (G) at the Planck scale. Thus, we will be able to verify the veracity of Dirac’s belief about the existence of “coincidences” between dimensionless ratios of subatomic and cosmological quantities, leading to a variation of G with time, that is, the ratio of the electrostatic to gravitational forces between an electron and a proton (∼1041) is roughly equal to the age of the universe divided by an elementary time constant, so that the strength of gravity, as determined by G, must vary inversely with time in the approximation of lower temperature or for times very far from the early period, to compensate for the time-variation of the Hubble parameter (H ∼ t−1). In short, we will show the validity of Dirac’s hypothesis only for times very far from the early period or T ≪ TP (∼1032 K).

scholarly journals Do Low Luminosity Stars Matter?

2009 ◽  
Vol 5 (H15) ◽  
pp. 47-60
Author(s):  
María Teresa Ruiz
Keyword(s):  
White Dwarf ◽  
Galactic Plane ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Missing Mass ◽  
Low Mass ◽  
Astronomical Research ◽  
Red Giant ◽  
Large Telescopes ◽  
The Universe

AbstractHistorically, low luminosity stars have attracted very little attention, in part because they are difficult to see except with large telescopes, however, by neglecting to study them we are leaving out the vast majority of stars in the Universe. Low mass stars evolve very slowly, it takes them trillions of years to burn their hydrogen, after which, they just turn into a He white dwarf, without ever going through the red giant phase. This lack of observable evolution partly explains the lack of interest in them. The search for the “missing mass” in the galactic plane turned things around and during the 60s and 70s the search for large M/L objects placed M-dwarfs and cool WDs among objects of astrophysical interest. New fields of astronomical research, like BDs and exoplanets appeared as spin-offs from efforts to find the “missing mass”. The search for halo white dwarfs, believed to be responsible for the observed microlensing events, is pursued by several groups. The progress in these last few years has been tremendous, here I present highlights some of the great successes in the field and point to some of the still unsolved issues.

scholarly journals Resolving the Hubble Constant Discrepancy: Revisiting the Effect of Local Environments

2020 ◽  
Vol 2 (1) ◽  
pp. 94-96
Author(s):  
Dennis M Doren ◽  
James Harasymiw
Keyword(s):  
Mass Density ◽  
Hubble Constant ◽  
Local Environment ◽  
Expansion Rate ◽  
Local Environments ◽  
The Universe

Studies have found two differing sets of figures for the Hubble constant without clear direction for resolution of that difference. This article offers a direction for reconciling the measurement discrepancy. Research is reviewed and theory is described that indicate the resolution may be found in revisiting how the degree of mass in local environments affects computations. The idea that the expansion rate of the universe is invariably uniform is discounted, to be replaced by a range of figures depending on the mass density of the local environment underlying the measurement.

scholarly journals The flatness problem and the age of the Universe

2020 ◽  
Vol 495 (4) ◽  
pp. 3571-3575
Author(s):  
Phillip Helbig
Keyword(s):  
Early Universe ◽  
Time Scale ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
Fine Tuning ◽  
Density Parameter ◽  
Age Of The Universe ◽  
Short Time ◽  
The Universe ◽  
Flatness Problem

ABSTRACT Several authors have made claims, none of which has been rebutted, that the flatness problem, as formulated by Dicke and Peebles, is not really a problem but rather a misunderstanding. Nevertheless, the flatness problem is still widely perceived to be real. Most of the arguments against the idea of a flatness problem are based on the change with time of the density parameter Ω and normalized cosmological constant λ and, since the Hubble constant H is not considered, are independent of time-scale. An independent claim is that fine-tuning is required in order to produce a Universe which neither collapsed after a short time nor expanded so quickly that no structure formation could take place. I show that this claim does not imply that fine-tuning of the basic cosmological parameters is necessary, in part for similar reasons as in the more restricted flatness problem and in part due to an incorrect application of the idea of perturbing the early Universe in a gedankenexperiment; I discuss some typical pitfalls of the latter.

Bianchi type I Universe: An extension of ΛCDM model

2021 ◽  
pp. 2150069
Author(s):  
Rajendra Prasad ◽  
Lalit Kumar Gupta ◽  
A. Beesham ◽  
G. K. Goswami ◽  
Anil Kumar Yadav
Keyword(s):  
Bianchi Type ◽  
Hubble Constant ◽  
Model Parameters ◽  
Constant Density ◽  
Data Sets ◽  
Type I ◽  
Data Set ◽  
Bianchi Type I ◽  
Age Of The Universe ◽  
The Universe

In this paper, we investigate a Bianchi type I exact Universe by taking into account the cosmological constant as the source of energy at the present epoch. We have performed a [Formula: see text] test to obtain the best fit values of the model parameters of the Universe in the derived model. We have used two types of data sets, viz., (i) 31 values of the Hubble parameter and (ii) the 1048 Pantheon data set of various supernovae distance moduli and apparent magnitudes. From both the data sets, we have estimated the current values of the Hubble constant, density parameters [Formula: see text] and [Formula: see text]. The dynamics of the deceleration parameter shows that the Universe was in a decelerating phase for redshift [Formula: see text]. At a transition redshift [Formula: see text], the present Universe entered an accelerating phase of expansion. The current age of the Universe is obtained as [Formula: see text] Gyrs. This is in good agreement with the value of [Formula: see text] calculated from the Plank collaboration results and WMAP observations.

Physical consequences of a general excess of charge

1959 ◽  
Vol 252 (1270) ◽  
pp. 313-333 ◽  
Keyword(s):  
Maxwell Equations ◽  
Direct Action ◽  
Hubble Constant ◽  
Mass Motion ◽  
Energy Tensor ◽  
Excess Charge ◽  
De Sitter ◽  
Hydrogen Atoms ◽  
Physical Consequences ◽  
The Universe

The possibility of a general excess of charge in the universe is proposed. If such exists, even to the extent of only 2 parts in 10 18 , sufficiently powerful electric forces result to produce the observed expansion of the universe on the basis of Newtonian mechanics. If the excess occurs as a slight difference in magnitude of the proton and electron charges, the hypothesis may be on the verge of what could be established by experiment. If creation of matter, and also necessarily charge, is assumed, the Maxwell equations must be modified to avoid strict conservation. The appropriate modification is shown to involve additional terms in the current and charge-density equations proportional to the vector and scalar potentials. When applied to a spherically symmetrical smoothed-out universe, the revised equations establish almost rigorously that electrical requirements imply a strict velocitydistance law for the mass motion of expansion. For agreement with observation, the requisite charge on the proton would be (1 + y ) e where y = 2 x 10 -18 , or, if the charges are strictly equal in magnitude, it requires 1 + y protons for every electron, with the same value of y . The value of the Hubble constant and of the smoothed-out density of matter in the universe are shown to be simply related by the theory to the rate of creation. The same solution is shown to hold equally in de Sitter space-time, and the principle of complete equivalence of all observers at all times is thereby demonstrated to be a property of the solution. Construction of the corresponding stress-energy tensor enables the factor associated with the new terms in the Maxwell equations to be directly related to the observable radius of the universe. On the first form of the charge-excess hypothesis, galaxies and clusters of galaxies (with their haloes) arise as ionized condensation units within the general background distribution. Since the units are conducting, they remain electrically neutral, and therefore grow and are controlled by ordinary gravitational forces. Moreover, because they are conducting, the units will expel their excess charge in the form of free protons. It is shown that the electrostatic potential at the surface of a unit is maintained by creation at such a value that the protons are expelled with energies corresponding to the highest energy cosmic rays. These units will take part in the general expansion, not under the direct action of the electric repulsion, but because they form and grow from the expanding background material. Any small departure in velocity of a unit from the local value would be quickly removed through the gravitational braking action associated with accretion of further material. The gravitational potential at the surface of a unit is such that infalling hydrogen atoms will have energy of motion corresponding to temperature of the order of a million degrees, and the outer parts of the units at least will be at high temperature.

scholarly journals The first galactic stars and chemical enrichment in the halo

2009 ◽  
Vol 5 (S265) ◽  
pp. 81-89
Author(s):  
Piercarlo Bonifacio
Keyword(s):  
Chemical Composition ◽  
High Mass ◽  
Mass Star ◽  
Low Mass Stars ◽  
Chemical Enrichment ◽  
The Galaxy ◽  
Low Metallicity ◽  
Low Mass ◽  
Indirect Information ◽  
The Universe

AbstractThe cosmic microwave background and the cosmic expansion can be interpreted as evidence that the Universe underwent an extremely hot and dense phase about 14 Gyr ago. The nucleosynthesis computations tell us that the Universe emerged from this state with a very simple chemical composition: H, 2H, 3He, 4He, and traces of 7Li. All other nuclei where synthesised at later times. Our stellar evolution models tell us that, if a low-mass star with this composition had been created (a “zero-metal” star) at that time, it would still be shining on the Main Sequence today. Over the last 40 years there have been many efforts to detect such primordial stars but none has so-far been found. The lowest metallicity stars known have a metal content, Z, which is of the order of 10−4Z⊙. These are also the lowest metallicity objects known in the Universe. This seems to support the theories of star formation which predict that only high mass stars could form with a primordial composition and require a minimum metallicity to allow the formation of low-mass stars. Yet, since absence of evidence is not evidence of absence, we cannot exclude the existence of such low-mass zero-metal stars, at present. If we have not found the first Galactic stars, as a by product of our searches we have found their direct descendants, stars of extremely low metallicity (Z ≤ 10−3Z⊙). The chemical composition of such stars contains indirect information on the nature of the stars responsible for the nucleosynthesis of the metals. Such a fossil record allows us a glimpse of the Galaxy at a look-back time equivalent to redshift z = 10, or larger. The last ten years have been full of exciting discoveries in this field, which I will try to review in this contribution.

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