A COSMOLOGY WITH A TIME AND SPACE COORDINATE-DEPENDENT SCALE FACTOR

1995 ◽  
Vol 10 (26) ◽  
pp. 1887-1894
Author(s):  
C.W. KIM ◽  
A. SINIBALDI ◽  
J. SONG
Keyword(s):  
Einstein Equation ◽  
Globular Clusters ◽  
Scale Factor ◽  
Time And Space ◽  
Cosmic Scale ◽  
Walker Metric ◽  
Space Coordinate ◽  
Age Of The Universe ◽  
The Universe

Based on the increase of Ω0 as a function of cosmic scale, the Robertson-Walker metric and the Einstein equation are generalized so that Ω0, H0 and the age of the Universe, to, all become functions of cosmic scales at which we observe them. The calculated local (within our galaxy) age of the Universe is about 18 Gyr, consistent with the ages of the oldest stars and globular clusters in our galaxy, while the ages at distant scales are shorter than the local age, solving the age puzzle. It is also shown that H0 becomes scale-dependent.

scholarly journals A PROPOSED SCALE-DEPENDENT COSMOLOGY FOR THE INHOMOGENEOUS UNIVERSE

1996 ◽  
Vol 05 (03) ◽  
pp. 293-312 ◽  
Author(s):  
C.W. KIM ◽  
J. SONG
Keyword(s):  
Hubble Parameter ◽  
Globular Clusters ◽  
Observational Cosmology ◽  
Energy Tensor ◽  
Stress Energy Tensor ◽  
Inhomogeneous Universe ◽  
Stress Energy ◽  
Walker Metric ◽  
Age Of The Universe ◽  
The Universe

We propose a scale-dependent cosmology with the stress-energy tensor of viscous fluid, in which the Robertson-Walker metric and the Einstein equation are generalized in such a way that Ω0, H0 and the age of the Universe all become scale-dependent. Its implications on the observational cosmology and possible modifications of the standard Friedmann cosmology are discussed. For example, since the age of the Universe in this model depends on the local values of Ω0 and the Hubble parameter, the age of the locally open Universe even with the high value of hubble parameter can be long enough to accommodate the measured ages of the oldest stars and globular clusters.

scholarly journals Hipparcos subdwarfs and globular cluster ages: towards reliable absolute ages

1997 ◽  
Vol 189 ◽  
pp. 433-438 ◽  
Author(s):  
F. Pont ◽  
M. Mayor ◽  
C. Turon
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Large Fraction ◽  
Age Determination ◽  
Colour Scale ◽  
Minimum Age ◽  
Age Of The Universe ◽  
Robust Prediction ◽  
The Universe ◽  
Cluster Age

The maximum age of galactic globular clusters provides the best observational constraint on the minimum age of the Universe. One of the main “missing link” in the globular cluster age determination has been the lack of a precise calibration, with local subdwarfs, of the position of the subdwarf sequence at different [Fe/H].Hipparcos data may change this situation. As many precise parallaxes become available for local subdwarfs, the distance to globular clusters can be estimated directly from ZAMS fitting to the subdwarf locus. The ages can then be inferred from the turnoff luminosity (a robust prediction of stellar evolution models), rather than using secondary indicators such as Horizontal-Branch position, or indicators depending on the uncertain colour scale such as turnoff colour.Combining Hipparcos parallaxes with [Fe/H] values determined with the CORAVEL spectrometer, we are studying the position of the subdwarfs in the Colour-Magnitude Diagram from a sample of more than 900 subdwarf candidates. Preliminary results are presented here. It is shown that the distances of many subdwarfs had been underestimated in previous studies, mainly because a large fraction of them is in fact evolved off the main sequence into the turnoff or the subgiant branch.

scholarly journals Cosmological consequences of a variable cosmological constant model

2016 ◽  
Vol 26 (07) ◽  
pp. 1750060 ◽  
Author(s):  
Hemza Azri ◽  
A. Bounames
Keyword(s):  
Cosmological Constant ◽  
Vacuum Energy ◽  
Gravitational Constant ◽  
Scale Factor ◽  
Accelerated Expansion ◽  
Variable Cosmological Constant ◽  
Age Of The Universe ◽  
Two Phases ◽  
Limiting Case ◽  
The Universe

We derive a model of dark energy which evolves with time via the scale factor. The equation-of-state is studied as a function of a parameter [Formula: see text] introduced in this model as [Formula: see text]. In addition to the recent accelerated expansion, the model predicts another decelerated phase. These two phases are studied via the parameter [Formula: see text]. The age of the universe is found to be almost consistent with the observation. In the limiting case, the cosmological constant model, we find that vacuum energy gravitates with a tiny gravitational constant which evolves with the scale factor, rather than with Newton’s constant. This enables degravitation of the vacuum energy which in turn produces the tiny observed curvature, rather than a 120 orders of magnitude larger value.

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 Stellar Encounters in Dense Systems

1996 ◽  
Vol 174 ◽  
pp. 243-252
Author(s):  
Melvyn B. Davies
Keyword(s):  
Globular Clusters ◽  
Large Fraction ◽  
Close Encounter ◽  
Solar Neighbourhood ◽  
Number Density ◽  
Age Of The Universe ◽  
The Universe ◽  
Nuclei Number

The number density of stars in the solar neighbourhood is sufficiently low that encounters between two stars will be extremely rare. However, in the cores of globular clusters, and glactic nuclei, number densities are sufficiently high (∼ 105 stars/pc3 in some systems) that encounter timescales can be comparable, or even less than, the age of the universe. In other words, a large fraction of the stars in these systems will have suffered from at least one close encounter or collision in their lifetime.

scholarly journals Distances and ages of globular clusters

2007 ◽  
Vol 3 (S248) ◽  
pp. 440-442 ◽  
Author(s):  
B. Chaboyer
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Formation History ◽  
Minimum Age ◽  
History Of ◽  
The Mean ◽  
Age Of The Universe ◽  
The Universe ◽  
Age Determinations

AbstractAs the oldest objects whose ages can be accurately determined, Galactic globular clusters can be used to establish the minimum age of the universe (and hence, to constrain cosmological models) and to study the early formation history of the Milky Way. The largest uncertainty in the determination of globular cluster ages is the distance scale. The current uncertainty in the distances to globular clusters is ~ 6%, which leads to a 13% uncertainty in the absolute ages of globular clusters. I am the PI on a SIM-Planetquest key project to determine the distances of 21 globular clusters with an accuracy of ranging from 1 to 4%. This will lead to age determinations accurate to 5 − 9%. The mean age of the oldest, most metal-poor globular clusters will be determined with an accuracy of ±3%.

scholarly journals The age of the Universe with globular clusters: reducing systematic uncertainties

2021 ◽  
Vol 2021 (08) ◽  
pp. 017
Author(s):  
David Valcin ◽  
Raul Jimenez ◽  
Licia Verde ◽  
José Luis Bernal ◽  
Benjamin D. Wandelt
Keyword(s):  
Globular Clusters ◽  
Systematic Uncertainties ◽  
Age Of The Universe ◽  
The Universe

scholarly journals The Main Sequence of the Very Old Globular Cluster NGC 6397

1980 ◽  
Vol 85 ◽  
pp. 423-423
Author(s):  
Gonzalo Alcaino ◽  
William Liller
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Narrow Range ◽  
Age Determination ◽  
The Sun ◽  
Age Of The Universe ◽  
The Universe ◽  
Photographic Photometry ◽  
Collapse Phase

We present photographic photometry for 1135 stars in the globular cluster NGC 6397, which, at a distance of 2.4 kpc, is most likely the second nearest globular to the Sun. The Racine wedge with the CTIO Yale 1 m telescope (Δm=3. 60 mag), the CTIO 4 m telescope (Δm=6. 83 mag) and the ESO 3.6 m telescope (Δm=3. 87 mag) was used to extend the photoelectric calibration from V≃16.1 to V≃20.7. The main sequence turnoff at V=16.7 and B-V=0.52 with respectively Mv =4.30 and (B-V)o =0.36 yields (m-M)v=12.40 and E(B-V)=0.16. Using the models of Iben and Rood (1970) and the isochrones of Demarque and McClure (1977), we deduce the cluster's age to be 17 × 109 years. This makes this object the oldest of the nine globular clusters with age determination and gives a lower limit to the age of the universe, rendering Ho ≤ 57 km sec−1 Mpc−1 if qo ≥ 0 is assumed. The large age spread of 6 billion years between NGC 6397 and 47 Tuc (the youngest counterpart with age data) indicates both that the protogalaxy underwent a slow collapse phase and that the abundances in globular clusters are lower for the oldest. The fact that the galactocentric distances for these clusters have the narrow range of 6 <R < 13 kpc makes it highly important to secure age data for extremely metal poor globulars far out in the halo.

scholarly journals A discrete-time interpretation of the Planck-Einstein equation

2006 ◽  
Vol 2006 ◽  
pp. 1-5
Author(s):  
A. Boyarsky
Keyword(s):  
String Theory ◽  
Quantum Gravity ◽  
Einstein Equation ◽  
Discrete Time ◽  
Loop Quantum Gravity ◽  
Empty Space ◽  
Important Conclusion ◽  
Age Of The Universe ◽  
The Times ◽  
The Universe

An important conclusion of both string theory and loop quantum gravity theory is that space and time are ultimately discrete. A consequence of discrete space is that there is empty space between the basic elements of space. Analogously, there are empty times between the times where time exists. When time does not exist, it is meaningless to consider the existence of the universe. In this note we consider a discrete-time interpretation of the Planck-Einstein equation and draw a curious conclusion about the real age of the universe.

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