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Particle horizon
About: Particle horizon is a research topic. Over the lifetime, 2096 publications have been published within this topic receiving 69137 citations.
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TL;DR: The cosmological constant may be non-zero as mentioned in this paper, which forces us to re-evaluate standard notions about the connection between geometry and the fate of our universe, and it is shown that there is no set of cosmology observations we can perform that will unambiguously allow us to determine what the ultimate destiny of the universe will be.
Abstract: The recognition that the cosmological constant may be non-zero forces us to re-evaluate standard notions about the connection between geometry and the fate of our Universe. An open Universe can recollapse, and a closed Universe can expand forever. As a corollary, we point out that there is no set of cosmological observations we can perform that will unambiguously allow us to determine what the ultimate destiny of the Universe will be.
36 citations
TL;DR: In this article, the authors discuss astronomical and astrophysical evidence, which relate to the principle of zero-total energy of the universe, that imply several relations among the mass M, the radius R and the angular momentum L of a sphere representing a Machian universe.
Abstract: We discuss astronomical and astrophysical evidence, which we relate to the principle of zero-total energy of the Universe, that imply several relations among the mass M, the radius R and the angular momentum L of a “large” sphere representing a Machian Universe. By calculating the angular speed, we find a peculiar centripetal acceleration for the Universe. This is an ubiquituous property that relates one observer to any observable. It turns out that this is exactly the anomalous acceleration observed on the Pioneers spaceships. We have thus shown that this anomaly is to be considered a property of the Machian Universe. We discuss several possible arguments against our proposal.
36 citations
TL;DR: A promising new method, the evolution of the number density of clusters with time, provides the most powerful indication so far that the universe has a subcritical density.
Abstract: How much matter is there in the universe? Does the universe have the critical density needed to stop its expansion, or is the universe underweight and destined to expand forever? We show that several independent measures, especially those utilizing the largest bound systems known—clusters of galaxies—all indicate that the mass-density of the universe is insufficient to halt the expansion. A promising new method, the evolution of the number density of clusters with time, provides the most powerful indication so far that the universe has a subcritical density. We show that different techniques reveal a consistent picture of a lightweight universe with only ∼20–30% of the critical density. Thus, the universe may expand forever.
36 citations
TL;DR: In this paper, the authors present exact solutions which presumably describe black holes in the background of a spatially flat, pressureless dark-matter, or dark matter plus dark energy, or quintom-dominated universe.
Abstract: We present new exact solutions which presumably describe black holes in the background of a spatially flat, pressureless dark-matter-- or dark matter plus dark energy ($\mathrm{DM}+\mathrm{DE}$)- or quintom-dominated Universe. These solutions generalize Lema\^{\i}tre-Tolman-Bondi metrics. For a dark-matter-- or ($\mathrm{DM}+\mathrm{DE}$)-dominated universe, the area of the black hole apparent horizon (AH) decreases with the expansion of the Universe while that of the cosmic AH increases. However, for a quintom-dominated universe, the black hole AH first shrinks and then expands, while the cosmic AH first expands and then shrinks. A ($\mathrm{DM}+\mathrm{DE}$)-dominated universe containing a black hole will evolve to the Schwarzschild-de Sitter solution with both AHs approaching constant size. In a quintom-dominated universe, the black hole and cosmic AHs will coincide at a certain time, after which the singularity becomes naked, violating cosmic censorship.
36 citations
TL;DR: In this paper, the authors apply the scale-relativistic resolution transformation to scale transformations in the early universe and propose a generalization of fundamental dilations laws, which are invariant under dilations.
Abstract: The principle of relativity, when it is applied to scale transformations, leads to the suggestion of a generalization of fundamental dilations laws. These new specialscale-relativistic resolution transformations involve log-Lorentz factors and lead to the occurrence of a minimal and of a maximal length-scale in nature, which are invariant under dilations. The minimal length-scale, that replaces the zero from the viewpoint of its physical properties, is identied with the Planck-length lP , and the maximal scale, that replaces innit y, is identied with the cosmic scale I L = 1=2 , where is the cosmological constant. The new interpretation of the Planck scale has several implications for the structure and history of the early Universe: we consider the questions of the origin, of the status of physical laws at very early times, of the horizon / causality problem and of uctuations at recombination epoch. The new interpretation of the cosmic scale has consequences for our knowledge of the present universe, concerning in particular Mach’s principle, the large number coincidence, the problem of the vacuum energy density, the nature and the value of the cosmological constant. The value (theroretically predicted ten years ago) of the scaled cosmological constant = 0:75 0:15 is now supported by several dieren t experiments (Hubble diagram of Supernovae, Boomerang measurements, gravitational lensing by clusters of galaxies). The scale-relativity framework also allows one to suggest a general solution to the missing mass problem, and to make theoretical predictions of fundamental energy scales, thanks to the interpretation of new structures in scale space: fractal /classical transitions as Compton lengths, mass-coupling relations and critical value 4 2 of inverse couplings. Among them, we nd a structure at 3:27 0:26 10 20 eV, which agrees closely with the observed highest energy cosmic rays at 3:2 0:9 10 20 eV, and another at 5:3 10 3 eV, which corresponds to the typical neutrino mass needed
35 citations