Realistic cosmological measurement of distances in the Friedmann universe

2016 ◽  
Vol 31 (02n03) ◽  
pp. 1641013 ◽  
Author(s):  
Aleksei Nikolaev ◽  
Sergey Chervon
Keyword(s):  
Measurement Method ◽  
Small Deviation ◽  
Duality Relation ◽  
Angular Diameter ◽  
Accelerated Expansion ◽  
Friedmann Universe ◽  
Angular Diameter Distance ◽  
Light Rays ◽  
Expansion Of The Universe ◽  
The Universe

We consider application of our development of Zeldovich’s ideas, presented in Ref. 1, for measurement of the cosmological angular diameter distance (ADD) in the Friedmann Universe. To make a comparison with [Formula: see text]CDM we analyze ADD measurement in [Formula: see text]CDM model responsible for the later inflation (present accelerated expansion of the Universe). We also analyze a small deviation from equality in the distance duality relation induced by the fullness (by matter) of the cone of light rays (CLR) which is used for the ADD measurement method.

scholarly journals The failure of testing for cosmic opacity via the distance-duality relation

2020 ◽  
Vol 497 (1) ◽  
pp. 378-388
Author(s):  
Václav Vavryčuk ◽  
Pavel Kroupa
Keyword(s):  
Cosmological Model ◽  
Convincing Evidence ◽  
Duality Relation ◽  
Angular Diameter ◽  
Luminosity Distance ◽  
Angular Diameter Distance ◽  
Frequency Independent ◽  
Unique Interpretation ◽  
The Universe

ABSTRACT The distance-duality relation (DDR) between the luminosity distance DL and the angular diameter distance DA is viewed as a powerful tool for testing for the opacity of the Universe, being independent of any cosmological model. It was applied by many authors, who mostly confirm its validity and report a negligible opacity of the Universe. Nevertheless, a thorough analysis reveals that applying the DDR in cosmic opacity tests is tricky. Its applicability is strongly limited because of a non-unique interpretation of the DL data in terms of cosmic opacity and a rather low accuracy and deficient extent of currently available DA data. Moreover, authors usually assume that cosmic opacity is frequency independent and parametrize it in their tests by a prescribed phenomenological function. In this way, they only prove that cosmic opacity does not follow their assumptions. As a consequence, no convincing evidence of transparency of the universe using the DDR has so far been presented.

Cosmological constant

2018 ◽  
Author(s):  
Michael Kachelriess
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Vacuum Fluctuations ◽  
Present Epoch ◽  
Modify Gravity ◽  
Expansion Of The Universe ◽  
The Universe

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

scholarly journals Taxonomy of Dark Energy Models

Universe ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 163
Author(s):  
Verónica Motta ◽  
Miguel A. García-Aspeitia ◽  
Alberto Hernández-Almada ◽  
Juan Magaña ◽  
Tomás Verdugo
Keyword(s):  
Dark Energy ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Energy Component ◽  
The Past ◽  
Energy Models ◽  
The Status ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Unknown Component

The accelerated expansion of the Universe is one of the main discoveries of the past decades, indicating the presence of an unknown component: the dark energy. Evidence of its presence is being gathered by a succession of observational experiments with increasing precision in its measurements. However, the most accepted model for explaining the dynamic of our Universe, the so-called Lambda cold dark matter, faces several problems related to the nature of such energy component. This has led to a growing exploration of alternative models attempting to solve those drawbacks. In this review, we briefly summarize the characteristics of a (non-exhaustive) list of dark energy models as well as some of the most used cosmological samples. Next, we discuss how to constrain each model’s parameters using observational data. Finally, we summarize the status of dark energy modeling.

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.

Heuristic determination of the cosmological constant

2021 ◽  
pp. 2150114
Author(s):  
Manuel Urueña Palomo ◽  
Fernando Pérez Lara
Keyword(s):  
Field Theory ◽  
Energy Density ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Fundamental Constants ◽  
Quantum Field ◽  
Brute Force ◽  
Expansion Of The Universe ◽  
The Universe

The vacuum catastrophe results from the disagreement between the theoretical value of the energy density of the vacuum in quantum field theory and the estimated one observed in cosmology. In a similar attempt in which the ultraviolet catastrophe was solved, we search for the value of the cosmological constant by brute-force through computation. We explore combinations of the fundamental constants in physics performing a dimensional analysis, in search of an equation resulting in the measured energy density of the vacuum or cosmological constant that is assumed to cause the accelerated expansion of the universe.

scholarly journals Can accelerated expansion of the universe be due to spacetime vorticity?

2018 ◽  
Vol 33 (40) ◽  
pp. 1850240
Author(s):  
Babur M. Mirza
Keyword(s):  
Magnetic Field ◽  
Accelerated Expansion ◽  
Newtonian Gravity ◽  
Hubble’S Parameter ◽  
Cosmic Expansion ◽  
Zero Curvature ◽  
Expansion Of The Universe ◽  
General Relativistic ◽  
The Universe ◽  
The Magnetic Field

We present here a general relativistic mechanism for accelerated cosmic expansion and the Hubble’s parameter. It is shown that spacetime vorticity coupled to the magnetic field density in galaxies causes the galaxies to recede from one another at a rate equal to the Hubble’s constant. We therefore predict an oscillatory universe, with zero curvature, without assuming violation of Newtonian gravity at large distances or invoking dark energy/dark matter hypotheses. The value of the Hubble’s constant, along with the scale of expansion, as well as the high isotropy of CMB radiation are deduced from the model.

scholarly journals Present accelerated expansion of the universe from new Weyl-integrable gravity approach

2014 ◽  
Vol 74 (11) ◽  
Author(s):  
Ricardo Aguila ◽  
José Edgar Madriz Aguilar ◽  
Claudia Moreno ◽  
Mauricio Bellini
Keyword(s):  
Accelerated Expansion ◽  
Expansion Of The Universe ◽  
The Universe

scholarly journals Is the expansion of universe accelerating or the Photons decelerating?

2015 ◽  
Vol 3 (1) ◽  
pp. 40
Author(s):  
Hasmukh Tank
Keyword(s):  
Big Bang ◽  
Time Dilation ◽  
Red Shift ◽  
Light Curves ◽  
Accelerated Expansion ◽  
Gravitational Acceleration ◽  
Expansion Of The Universe ◽  
Pi Mesons ◽  
The Big Bang ◽  
The Universe

<p>Astronomical observations of the cosmological red-shift are currently interpreted in terms of ‘expansion of universe’ and ‘accelerated-expansion of the universe’, at the rate of <em>H<sub>0</sub> c</em>; here <em>H<sub>0</sub></em> is Hubble’s constant, and c is the speed of light. Whereas a straight-forward derivation presented here suggests that: rather it is the photon which is decelerating, at the rate of <em>H<sub>0</sub> c</em>. Such a deceleration of photons can be caused by virtual electrons, positrons and pi-mesons, contained in the extra galactic quantum vacuum, because: they do have gravitational-acceleration of the same order as <em>H<sub>0</sub> c</em> at their “surfaces”; or by decay of a photon into a lighter photon and a particle of mass <em>h H<sub>0</sub> / c<sup>2</sup></em>. Tired-light interpretations of the cosmological red-shift’ were so far considered as not compatible with the observations of ‘time-dilation of super-novae light-curves’; so in a paper titled: “Wave-theoretical insight into the relativistic ‘length-contraction’ and ‘time-dilation of super-novae light-curves’” (Tank, Hasmukh K. 2013), it has been already shown that any mechanism which can cause ‘cosmological red-shift’ will also cause ‘time-dilation of super-novae light-curves’.  Therefore, we now need not to remain confined to the Big-Bang model of cosmology.</p>

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