scholarly journals Expanding Confusion: Common Misconceptions of Cosmological Horizons and the Superluminal Expansion of the Universe

2004 ◽  
Vol 21 (1) ◽  
pp. 97-109 ◽  
Author(s):  
Tamara M. Davis ◽  
Charles H. Lineweaver
Keyword(s):  
General Relativity ◽  
Confidence Level ◽  
Speed Of Light ◽  
Observable Universe ◽  
Expansion Of The Universe ◽  
Superluminal Expansion ◽  
The Universe ◽  
Recession Velocity ◽  
Common Misconceptions ◽  
Rule Out

AbstractWe use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the universe. To show the abundance of these misconceptions we cite numerous misleading, or easily misinterpreted, statements in the literature. In the context of the new standard ΛCDM cosmology we point out confusions regarding the particle horizon, the event horizon, the ‘observable universe’ and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests. Attempts to restrict recession velocities to less than the speed of light require a special relativistic interpretation of cosmological redshifts. We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23σ.

INFLATION, QUINTESSENCE PROBLEM AND VARYING SPEED OF LIGHT

2002 ◽  
Vol 17 (05) ◽  
pp. 295-302
Author(s):  
SUBENOY CHAKRABORTY
Keyword(s):  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Speed Of Light ◽  
Expansion Of The Universe ◽  
The Universe

In this paper it is shown that the present accelerated expansion of the Universe can be explained only by considering variation of the speed of light, without taking into account the cosmological constant or quintessence matter.

Gamma-Ray Bursts as Probes of the Universe

2011 ◽  
Author(s):  
Joshua S. Bloom
Keyword(s):  
Star Formation ◽  
Cosmic Rays ◽  
Gravitational Waves ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Ongoing Study ◽  
Observable Universe ◽  
History Of ◽  
Expansion Of The Universe ◽  
The Universe

This chapter focuses on how gamma-ray bursts (GRBs) are emerging as unique tools in the study of broad areas of astronomy and physics by virtue of their special properties. The unassailable fact about GRBs that makes them such great probes is that they are fantastically bright and so can be seen to the farthest reaches of the observable Universe. In parallel with the ongoing study of GRB events and progenitors, new lines of inquiry have burgeoned: using GRBs as unique probes of the Universe in ways that are almost completely divorced from the nature of GRBs themselves. Topics discussed include studies of gas, dust, and galaxies; the history of star formation; measuring reionization and the first objects in the universe; neutrinos, gravitational waves, and cosmic rays; quantum gravity and the expansion of the universe; and the future of GRBs.

scholarly journals DO RECENT SUPERNOVAE Ia OBSERVATIONS TEND TO RULE OUT ALL THE COSMOLOGIES?

2007 ◽  
Vol 16 (10) ◽  
pp. 1641-1651 ◽  
Author(s):  
RAM GOPAL VISHWAKARMA
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Gravitational Lensing ◽  
Weakly Interacting Massive Particles ◽  
Cosmological Models ◽  
Accelerated Expansion ◽  
Standard Candle ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Rule Out

Dark energy and the accelerated expansion of the universe have been the direct predictions of the distant supernovae Ia observations which are also supported, indirectly, by the observations of the CMB anisotropies, gravitational lensing and the studies of galaxy clusters. Today these results are accommodated in what has become the concordance cosmology: a universe with flat spatial sections t = constant with about 70% of its energy in the form of Einstein's cosmological constant Λ and about 25% in the form of dark matter (made of perhaps weakly-interacting massive particles). Though the composition is weird, the theory has shown remarkable successes at many fronts. However, we find that as more and more supernovae Ia are observed, more accurately and towards higher redshift, the probability that the data are well-explained by the cosmological models decreases alarmingly, finally ruling out the concordance model at more than 95% confidence level. This raises doubts against the "standard candle"-hypothesis of the supernovae Ia and their use in constraining the cosmological models. We need a better understanding of the entire SN Ia phenomenon in order to extract cosmological consequences from them.

scholarly journals CAN THE EXISTENCE OF DARK ENERGY BE DIRECTLY DETECTED?

2009 ◽  
Vol 24 (18n19) ◽  
pp. 3426-3436 ◽  
Author(s):  
MARTIN L. PERL
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Total Mass ◽  
Mass Density ◽  
Mass Energy ◽  
Dark Energy Density ◽  
Astronomical Observations ◽  
Expansion Of The Universe ◽  
The Universe

Over the last decade, astronomical observations show that the acceleration of the expansion of the universe is greater than expected from our understanding of conventional general relativity, the mass density of the visible universe, the size of the visible universe and other astronomical measurements. The additional expansion has been attributed to a variety of phenomenon that have been given the general name of dark energy. Dark energy in the universe seems to comprise a majority of the energy in the visible universe amounting to about three times the total mass energy. But locally the dark energy density is very small. However it is not zero. In this paper I describe the work of others and myself on the question of whether dark energy density can be directly detected. This is a work-in-progress and I have no answer at present.

Bulk viscosity in Friedmann universe with a varying speed of light described by modified equation of state

2015 ◽  
Vol 12 (10) ◽  
pp. 1550126
Author(s):  
G. S. Khadekar ◽  
Arti Ghogre
Keyword(s):  
Equation Of State ◽  
Bulk Viscosity ◽  
Scale Factor ◽  
Special Choice ◽  
Speed Of Light ◽  
Dependent Parameter ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Modified Equation ◽  
Universe Evolution

We solve the Freidmann equations by considering a universe media as a bulk viscosity described by a modified equation of state (EOS) of the form p = (γ - 1)ρc2 + Λ(t). A completely integrable dynamical equation to the scale factor is obtained and gives out the exact solution by assuming that the time-dependent parameter Λ and the bulk viscosity are linear combination of two and three terms, respectively and is expressed as: [Formula: see text] and [Formula: see text], where R is a scale factor and Λ0, Λ1, ζ0, ζ1, ζ2, are constants. For a special choice of the parameters, we discuss the acceleration expansion of the universe evolution and future singularities in the framework of variable speed of light (VSL) theory.

scholarly journals Optical Illusion by Red Shif

2019 ◽  
Vol 2 (4) ◽  
Keyword(s):  
Milky Way ◽  
Blue Shift ◽  
Red Shift ◽  
Optical Illusion ◽  
Speed Of Light ◽  
System A ◽  
Expansion Of The Universe ◽  
The Universe

If all the stars outside our galaxy show the same red shift and pretend expansion of the universe, then it’s probably up to us. We know that the Milky Way is contracting. We expect a blue shift, which we cannot see. Instead of the blue shift, the stars of the Milky Way can be seen as fixed stars. The reason is that the distance is given in meters and decreases as much as the speed of light measured in meters per second. Although in our system a change in the speed of light is neither measurable nor observable, but it seems to be working.

scholarly journals How to Measure Gravitational Aberration?

2006 ◽  
Vol 2 (S240) ◽  
pp. 670-677
Author(s):  
Michal Křížek ◽  
Alena Šolcová
Keyword(s):  
A Priori ◽  
Hubble Constant ◽  
The Moon ◽  
Speed Of Light ◽  
Henri Poincaré ◽  
The Earth ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Equations With Delay ◽  
Two Bodies

AbstractIn 1905, Henri Poincaré predicted the existence of gravitational waves and assumed their speed equal to the speed of light. If additionally the gravitational aberration would have the same magnitude as the aberration of light, we would observe several paradoxical phenomena. For instance, the orbit of two bodies would be unstable, since two attractive forces arise that are not in line and hence form a couple. This will be modelled by a nonautonomous system of ordinary differential equations with delay. In fact, any positive value of the gravitational aberration increases the angular momentum of such a system and this may contribute to the expansion of the universe. We found a remarkable coincidence between the Hubble constant and the increasing distance of the Moon from the Earth.In 2000, Carlip showed that in general relativity gravitational aberration is almost cancelled out by velocity–dependent interactions. We show how the actual value of the gravitational aberration can be obtained by measurement of a single angle at a suitable time t* corresponding to the perihelion of an elliptic orbit. We also derive an a priori error estimate that expresses how accurately t* has to be determined to obtain the gravitational aberration to a prescribed tolerance.

scholarly journals Gravitational Waves from Compact Bodies

1996 ◽  
Vol 165 ◽  
pp. 153-183
Author(s):  
Kip S. Thorne
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Neutron Stars ◽  
Gravitational Radiation ◽  
Relativity Theory ◽  
Energy Concentration ◽  
Speed Of Light ◽  
General Relativity Theory ◽  
Concentration Changes ◽  
The Universe

According to general relativity theory, compact concentrations of energy (e.g., neutron stars and black holes) should warp spacetime strongly, and whenever such an energy concentration changes shape, it should create a dynamically changing spacetime warpage that propagates out through the Universe at the speed of light. This propagating warpage is called gravitational radiation — a name that arises from general relativity's description of gravity as a consequence of spacetime warpage.

Time as an Expanding Labyrinth of Information

KronoScope ◽  
2010 ◽  
Vol 10 (1-2) ◽  
pp. 64-76 ◽  
Author(s):  
Paul Halpern
Keyword(s):  
General Relativity ◽  
Classical Mechanics ◽  
Information Space ◽  
Interpretation Of Quantum Mechanics ◽  
Many Worlds ◽  
Cosmological Expansion ◽  
Expansion Of The Universe ◽  
The Many ◽  
The Universe ◽  
Dense State

AbstractWe propose a model of time in physics that combines the determinism of classical mechanics, the irreversibility of thermodynamics, and the ever-bifurcating strands of the Many Worlds Interpretation of quantum mechanics, by means of an expanding, labyrinthine information space. We speculate that the growth of this space is linked to the cosmological expansion of the universe from its initial dense state by means of a generalization of general relativity to include the information space.

scholarly journals Minimal extension of General Relativity: Alternative gravity model with non-minimal coupling between matter and curvature

2014 ◽  
Vol 11 (02) ◽  
pp. 1460003 ◽  
Author(s):  
Orfeu Bertolami ◽  
Jorge Páramos
Keyword(s):  
General Relativity ◽  
Lagrangian Density ◽  
Density Fluctuations ◽  
Accelerated Expansion ◽  
Minimal Extension ◽  
Minimal Coupling ◽  
Expansion Of The Universe ◽  
Scalar Theories ◽  
The Impact ◽  
The Universe

We examine an extension of General Relativity with an explicit non-minimal coupling between matter and curvature. The purpose of this work is to present an overview of the implications of the latter to various contexts, ranging from astrophysical matter distributions to a cosmological setting. Various results are discussed, including the impact of this non-minimal coupling on the choice of Lagrangian density, on a mechanism to mimic galactic and cluster dark matter, on the possibility of accounting for the accelerated expansion of the Universe, energy density fluctuations and modifications to post-inflationary reheating. The equivalence between a model exhibiting a non-minimal coupling and multi-scalar-theories is also discussed.

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