Related papers: Lemaitres Limit
The current acceleration of the universe can be modeled in terms of a cosmological constant. We show that the extremely small value of \Lambda L_P^2 ~ 3.4 x 10^{-122}, the holy grail of theoretical physics, can be understood in terms of a…
In 1937 Dirac proposed the large number hypothesis (LNH). The idea was to explain that these numbers were large because the Universe is old. A time variation of certain constants was assumed. So far, no experimental evidence has…
An estimate of the maximum observable redshift is obtained using only t_{0} approximately equal to (14+- 3)10^{9}years, H_{0} approximately equal to 65 +- 10Km\sec^{-1}Mpc^{-1}(t_{0}H_{0} approximately equal to 0.91 +- 0.08/0.18) assuming…
The effect of a cosmological constant on the precession of the line of apsides is O(\Lambda c^2 r^3/GM) which is 3(H_\circ P)^2/8\pi^2 \approx 10^{-23} for a vacuum-dominated Universe with Hubble constant H_\circ = 65 km/sec/Mpc and for the…
Measuring the rate at which the universe expands at a given time -- the 'Hubble constant' -- has been a topic of controversy since the first measure of its expansion by Edwin Hubble in the 1920's. As early as the 1970's, Sandage et de…
A measurement of the expansion rate of the Universe (that is the Hubble constant, H0) is derived here using the gamma-ray attenuation observed in the spectra of gamma-ray sources produced by the interaction of extragalactic gamma-ray…
As revealed by Hubble in 1928, our Universe is expanding. This discovery was fundamental to widening our horizons and our conception of space, and since then determining the rate at which our Universe is expanding has become one of the…
The diameter of the apparent horizon, defined by the distance between furthest points on the horizon, in spacetimes with a positive cosmological constant $\varLambda$ has been investigated. It is established that the diameter of the…
Friedmann-Lemaitre equations with contributions coming from matter, curvature, cosmological constant, and radiation, when written in terms of conformal time u rather than in terms of cosmic time t, can be solved explicitly in terms of…
It has recently been claimed that the Hubble Sphere represents a previously unknown limit to our view of the universe, with light we detect today coming from a proper distance less than this "Cosmic Horizon" at the present time. By…
From a fractal perspective, the entropy bound of gravitational systems undergoes changes. Furthermore, in the cosmological setting, the conservation law of a perfect fluid is also altered in such systems, affecting spatial elements like…
In this paper, we have investigated a bulk viscous anisotropic Universe and constrained its model parameters with recent $H(z)$ and Pantheon compilation data. Using cosmic chronometric technique, we estimate the present value of Hubble's…
We determine the density parameters $\Omega_m$ of gravitating matter and $\Omega_{\Lambda}$ of vacuum energy, by making a $\chi^2$ fit to nine independent astrophysical constraints. Paying rigorous attention to statistical detail, we find…
We use the quantum unimodular theory of gravity to relate the value of the cosmological constant, $\Lambda$, and the energy scale for the emergence of cosmological classicality. The fact that $\Lambda$ and unimodular time are complementary…
The hot big-bang cosmology provides a reliable accounting of the Universe from about $10^{-2}\sec$ after the bang until the present, as well as a robust framework for speculating back to times as early as $10^{-43}\sec$. Cosmology faces a…
When one combines multiverse predictions by Bousso, Hall, and Nomura for the observed age and size of the universe in terms of the proton and electron charge and masses with anthropic predictions of Carter, Carr, and Rees for these masses…
We investigate the cosmological implications of the generalized and extended uncertainty principle (GEUP), and whether it could provide an explanation for the dark energy. The consequence of the GEUP is the existence of a minimum and a…
A new cosmological model makes the following predictions: (1) The deceleration parameter $q_{0}$ is approximately zero. (2) The mass density parameter $\Omega_{m}$ is less than 1. (3) The universe is spatially closed, but is asymptotically…
Before the discovery of the expanding universe, one of the challenges faced in early relativistic cosmology was the determination of the finite and constant curvature radius of space-time by using astronomical observations. Great interest…
The ages of the oldest stellar objects in our galaxy provide an independent test of the current cosmological model as they give a lower limit to the age of the Universe. Recent accurate parallaxes by the Gaia space mission, accurate…