The Accelerating Expansion of the Universe

Physics Today ◽  
2005 ◽  
Vol 58 (4) ◽  
pp. 39-39
Author(s):  
John Updike
Keyword(s):  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

scholarly journals Almost-Pseudo-Ricci Symmetric FRW Universe with a Dynamic Cosmological Term and Equation of State

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 205
Author(s):  
Sanjay Mandal ◽  
Avik De ◽  
Tee-How Loo ◽  
Pradyumn Kumar Sahoo
Keyword(s):  
Equation Of State ◽  
Cosmological Parameters ◽  
Cosmological Term ◽  
Ricci Scalar ◽  
Energy Conditions ◽  
Late Time ◽  
Frw Universe ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

The objective of the present paper is to investigate an almost-pseudo-Ricci symmetric FRW spacetime with a constant Ricci scalar in a dynamic cosmological term Λ(t) and equation of state (EoS) ω(t) scenario. Several cosmological parameters are calculated in this setting and thoroughly studied, which shows that the model satisfies the late-time accelerating expansion of the universe. We also examine all of the energy conditions to check our model’s self-stability.

Spectral redshift does not imply an accelerating expansion of the universe

2013 ◽  
Vol 26 (3) ◽  
pp. 452-456
Author(s):  
Dimitrios Laskaroudis
Keyword(s):  
Red Shift ◽  
Gravity Center ◽  
Erroneous Conclusion ◽  
Minimum Value ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Creation ◽  
The Universe ◽  
Spectral Redshift

Spectra received from faraway heavenly objects display a redshift. In this paper, it is shown that there is a moment in time tx at which time the red shift has its minimum value. This moment is different for every object and depends on the distance of the emission from the gravity center of the object. So from the time of the creation of the object and up until the time tx, the red shift is decreasing and from that moment on it is increasing while the object, due to the expansion of the universe, continues to move away with decreasing speed. Due to the change of the red shift from decreasing to increasing, it is possible to observe faraway supernovas with a brightness that is less than what is expected. This observation leads to the erroneous conclusion that the universe is expanding with acceleration. Finally, an explanation is given to the fact that the number of quasars is decreasing in time.

scholarly journals ACCELERATING EXPANSION OF THE UNIVERSE MAY BE CAUSED BY INHOMOGENEITIES

2006 ◽  
Vol 21 (14) ◽  
pp. 1117-1125 ◽  
Author(s):  
GYULA BENE ◽  
VIKTOR CZINNER ◽  
MÁTYÁS VASÚTH
Keyword(s):  
Friedmann Equation ◽  
Additional Term ◽  
Density Fluctuations ◽  
Einstein Equations ◽  
The Other ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Homogeneous Approximation ◽  
Spatial Inhomogeneities

We point out that, due to the nonlinearity of the Einstein equations, a homogeneous approximation in cosmology leads to the appearance of an additional term in the Friedmann equation. This new term is associated with the spatial inhomogeneities of the metric and can be expressed in terms of density fluctuations. Although it is not constant, it decays much slower (as t-2/3) than the other terms (like density) which decrease as t-2. The presence of the new term leads to a correction in the scale factor that is proportional to t2and may give account of the recently observed accelerating expansion of the universe without introducing a cosmological constant.

Swampland criteria and cosmological behavior of Tsallis holographic dark energy in Bianchi -III Universe

2020 ◽  
Vol 17 (07) ◽  
pp. 2050098 ◽  
Author(s):  
Umesh Kumar Sharma ◽  
Shikha Srivastava ◽  
A. Beesham
Keyword(s):  
Dark Energy ◽  
Deceleration Parameter ◽  
Holographic Dark Energy ◽  
Accelerating Universe ◽  
Accelerating Expansion ◽  
Bianchi Iii ◽  
Expansion Of The Universe ◽  
Hubble Horizon ◽  
The Universe ◽  
Universe Evolution

In this paper, a new form of dark energy, known as Tsallis holographic dark energy (THDE), with IR cutoff as Hubble horizon proposed by Tavayef et al. Tsallis holographic dark energy, Phys. Lett. B 781 (2018) 195 has been explored in Bianchi-III model with the matter. By taking the time subordinate deceleration parameter, the solution of Einstein’s field equation is found. The Universe evolution from earlier decelerated to the current accelerated phase is exhibited by the deceleration parameter acquired in the THDE model. It can be seen that the derived THDE model is related to an accelerating Universe with quintessence ([Formula: see text]). The squared sound speed [Formula: see text] also suggests that the THDE model is classically stable at present. In addition, the quintessence phase of the THDE model is analyzed with swampland conjecture to reformulate the accelerating expansion of the Universe.

Rotation as a Source of Accelerating Expansion of the Universe

2021 ◽  
Author(s):  
Andrzej Szummer
Keyword(s):  
Gravitational Force ◽  
Cosmological Parameters ◽  
Classical Mechanics ◽  
Astronomical Observations ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Difference ◽  
Changes Over Time ◽  
The Universe ◽  
Over Time

Abstract Assuming a hypothesis, that the universe is rotating from the very beginning – as soon as it appeared- creates new possibilities to explain accelerating expansion of the universe. A spinning universe is under the action of two enormous forces: gravitational force and centrifugal force. The difference between the two forces has been shown to give the resultant force that causes the expansion of the universe to accelerate. Applying classical mechanics as a method, I calculated the magnitude of this acceleration, the time when it appeared and how it changes over time. By applying only recognized cosmological parameters, interesting results were obtained that can be checked with astronomical observations. The presence of acceleration of expansion causes the rate of expansion of the universe to continue to increase, which is consistent with astronomical observations. However, the speed of this increase in the rate of expansion becomes slower over time.

scholarly journals VISCOUS DARK ENERGY IN f(T) GRAVITY

2013 ◽  
Vol 28 (27) ◽  
pp. 1350118 ◽  
Author(s):  
M. SHARIF ◽  
SHAMAILA RANI
Keyword(s):  
Dark Energy ◽  
Graphical Representation ◽  
Teleparallel Gravity ◽  
Eos Parameter ◽  
Phantom Divide ◽  
Accelerating Expansion ◽  
Phantom Divide Line ◽  
Expansion Of The Universe ◽  
Crossing Of Phantom Divide ◽  
The Universe

We study the bulk viscosity taking dust matter in the generalized teleparallel gravity. We consider different dark energy (DE) models in this scenario along with a time-dependent viscous model to construct the viscous equation of state (EoS) parameter for these DE models. We discuss the graphical representation of this parameter to investigate the viscosity effects on the accelerating expansion of the universe. It is mentioned here that the behavior of the universe depends upon the viscous coefficients showing the transition from decelerating to accelerating phase. It leads to the crossing of phantom divide line and becomes phantom dominated for specific ranges of these coefficients.

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