Dark Matter and Dark Energy

2008

Phenomena currently attributed to Dark Energy (DE) and Dark Matter (DM) are merely a result of the interplay between gravitational energy density, generated by the contraction of space by matter, and the energy density of the Cosmological Microwave Background (CMB), which causes space dilation. In the universe, globally, the gravitational energy density equals the CMB energy density. This leads to the derivation of the Hubble parameter, H, as a function of the scale factor, a, the time, t, the redshift, z, and to the calculation of its present value. It also leads to a new understanding of the cosmological redshift and the Euclidian nature of the universe. From H(t) we conclude that the time derivative of a is constant. This is in contrast to the consensus of the last decade. This result is supported by the fit of our theoretically derived flux from supernovae (SN) as a function of z, with observation. This flux is derived based on our H(z) that determines DL, the Luminosity Distanc...

Science, 2015

A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of “dark matter,” a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of “dark energy,” energy associated with empty space. Both dark matter and dark energy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales.

Current Science, 2009

This review on dark energy is intended for a wider audience, beginners as well as experts. It contains important notes on various aspects of dark energy and its alternatives. The section on Newtonian cosmology followed by heuristic arguments to capture the pressure effects allows us to discuss the basic features of physics of cosmic acceleration without actually resorting to the framework of general theory of relativity. The brief discussion on observational aspects of dark energy is followed by a detailed exposition of underlying features of scalar field dynamic relevant to cosmology. The review includes pedagogical presentation of generic features of models of dark energy and its possible alternatives.

2008

One could call 2006 as the year of cosmology since in the year two US scientists were awarded by the Nobel prize for their studies of Cosmic Microwave Background (CMB) spectrum and anisotropy. Studies of CMB anisotropy done with the Soviet spacecraft Prognoz-9 by the Relikt-1 team are reminded. Problems of modern cosmology are outlined. We discuss conformal cosmology parameters

viXra, 2017

The Universe has a flat geometry and its density is very close to critical density. However, the observed amount of matter accounts for only 5% of the critical density. The rest of the 95% is completely unknown to us which exists in the form of Dark Energy (68%) and Dark Matter (27%). We present an overview of how the very idea of the existence of Dark Matter emerged and some compelling evidences for the existence of such matter. Moreover, we also provide an insight on how scientific ideas have evolved from a static Universe to an expanding Universe and then to an accelerating Universe. In addition, we explain fundamental concepts related to Dark Energy and discuss briefly on the evidences of Dark Energy. We also discuss some alternative solutions to the problems of Dark Matter and Dark Energy provided by different scientists.

The Review of Particle Physics, 2014

The accelerating expansion of the universe is the most surprising cosmological discovery in many decades. In this short review, we briefly summarize theories for the origin of cosmic acceleration and the observational methods being used to test these theories. We then discuss the current observational state of the field, with constraints from the cosmic microwave background (CMB), baryon acoustic oscillations (BAO), Type Ia supernovae (SN), direct measurements of the Hubble constant (H0), and measurements of galaxy and matter clustering. Assuming a flat universe and dark energy with a constant equation-of-state parameter w=P/ρ, the combination of Planck CMB temperature anisotropies, WMAP CMB polarization, the Union2.1 SN compilation, and a compilation of BAO measurements yields w=−1.10+0.08−0.07, consistent with a cosmological constant (w=−1). However, with these constraints the cosmological constant model predicts a value of H0 that is lower than several of the leading recent estimates, and it predicts a parameter combination σ8(Ωm)0.5 that is higher than many estimates from weak gravitational lensing, galaxy clusters, and redshift-space distortions. Individually these tensions are only significant at the ~2σ level, but they arise in multiple data sets with independent statistics and distinct sources of systematic uncertainty. The tensions are stronger with Planck CMB data than they were with WMAP because of the smaller statistical errors and the higher central value of Ωm. With the improved measurements expected from the next generation of data sets, these tensions may diminish, or they may sharpen in a way that points towards a more complete physical understanding of cosmic acceleration.

AIP Conference Proceedings, 2008

The discovery ten years ago that the expansion of the Universe is accelerating put in place the present cosmological model, in which the Universe is composed of 4% baryons, 20% dark matter, and 76% dark energy. Yet the underlying cause of cosmic acceleration remains a mystery: it could arise from the repulsive gravity of dark energy-for example, the quantum energy of the vacuum-or it may signal that General Relativity breaks down on cosmological scales and must be replaced. In these lectures, I present the observational evidence for cosmic acceleration and what it has revealed about dark energy, discuss a few of the theoretical ideas that have been proposed to explain acceleration, and describe the key observational probes that we hope will shed light on this enigma in the coming years. Based on five lectures given at the XII Ciclo de Cursos Especiais at the

2007

Nature, 2009

In terms of their contribution to the mean energy density, the contents of the Universe are approximately 75% dark energy, 20% dark matter and 5% normal (atomic) matter, with smaller contributions from photons and neutrinos. These measurements rely on the validity of the hot Big Bang model, general relativity and the cosmological principle (that the Universe is uniform on the largest scales). The breadth and depth of experiments and observations that support these under lying tenets give us confidence that this model of the cosmos has a solid foundation.

Brazilian Journal of Physics, 2001

Different physical phenomena, techniques, and evidences which give the proof for the existence of dark matter have been discussed.