Recent observation of supernovae type Ia show clearly that there is a large scale repulsive force in the Universe. Neither of the four known fundamental interactions can account for this repulsive force. Gravity is known to be the interaction responsible for the large scale structure and evolution of the Universe. The problem with gravity is that it gives rise to a force which is attractive only. Gravity theories, including General Relativity, deals with gravity as an attractive force. Although this is consistent with our experience in the solar system and other similar astrophysical systems, gravity theories fail to account for SN type Ia observation. So, we are in a real problem concerning the interpretation of these observation. This problem is only ten years old. In order to go out of this problematic situation, scientists have suggested the existence of a type of energy in the Universe that is responsible for the above mentioned repulsive force. They have given this type of energy the exotic term {\it "Dark Energy"}. Although this type of energy forms more than two thirds of the energetic contents of our Universe, its reasonable nature is missing in all gravity theories.
The aim of the present work is to review the present status of the problem of dark energy. Also, to suggest a new geometric solution for this problem.
Einstein's dream of describing elementary particles as solutions of a classical field theory is severely limited by our current understanding of Nature. Quantum theory is inconsistent with any local realistic theory such as evolving topological structures in space. It is shown that allowing time reversal as an intrinsic part of the structure of elementary particles allows general relativity to explain quantum theory in principle. Such structures may also explain electric charge and spin-half.
Uncompactified KK universes are so intrinsically connected to the otherwise only empirically required "missing" Dark Matter (DM), that: 1) They yield a simple prediction which explains both the enigma of the extra-dimensions' (XD) unobservability and the enigma of the present DM. The two enigmas are "annihilated" into the hypothesis of "missing light", or better of "photonland". This eliminates the very need to hypothesize/search/find DM-candidates of exceptional/exotic properties to explain their darkness. 2) An early, spontaneous gravitational XD-collapse of their natural 5D-DM replaces KK's…
Dark matter is among the most important open problems in both astrophysics and particle physics. We review the status of art of dark matter search at theoretical and experimental level discussing also alternative hypotheses.
The current concordance model of cosmology is dominated by two mysterious ingredients: dark matter and dark energy. In this paper, we explore the possibility that, in fact, there exist two dark-energy components: the cosmological constant $Λ$, with equation-of-state parameter $w_Λ=-1$, and a `missing matter' component $X$ with $w_X=-2/3$, which we introduce here to allow the evolution of the universal scale factor as a function of conformal time to exhibit a symmetry that relates the big bang to the future conformal singularity, such as in Penrose's conformal cyclic cosmology. Using recent cos…
In recent past, the progresses in accretion studies onto relativistically gravitating central objects like a Schwarzschild singularity reveal that the accretion flow must be transonic. For such cases, the radial inward speed gradient can be written as a numerator by denominator form among which the later vanishes somewhere in between infinite distance from the attracter to the event horizon of the same. For sustainability of a physical solutions, the numerator should vanish at the same radial distance where denominator does vanish. From this point, we obtain a second degree first order differe…
This paper is a sequel of the series of papers [gr-qc/9409010, gr-qc/9505034, gr-qc/9603022], being an immediate continuation and development of the latter of them. In the Friedmann universe, the equation $Ω_0=2q_0$ holds ($Ω$ is density parameter, $q$ is deceleration parameter, and subscript 0 indicates present-day values), which gives rise to the problem of the missing matter as observational data give $Ω_0<2q_0$. In the cosmic-length universe, $Ω_0=2q_0- L/R_0^3H_0^2$ ($R_0$ is the radius of the universe, $H_0$ is Hubble constant), which lifts the problem. The cosmic length, $L=const \appro…
Within the standard cosmological scenario the Universe is found to be filled by obscure components (dark matter and dark energy) for ~95% of its energy budget. In particular, almost all the matter content in the Universe is given by dark matter, which dominates the mass budget and drives the dynamics of galaxies and clusters of galaxies. Unfortunately, dark matter and dark energy have not been detected and no direct or indirected observations have allowed to prove their existence and amount. For this reason, some authors have suggested that a modification of Einstein Relativity or the change o…
We generalize tensor-scalar theories of gravitation by the introduction of an abnormally weighting type of energy. This theory of tensor-scalar anomalous gravity is based on a relaxation of the weak equivalence principle that is now restricted to ordinary visible matter only. As a consequence, the convergence mechanism toward general relativity is modified and produces naturally cosmic acceleration as an inescapable gravitational feedback induced by the mass-variation of some invisible sector. The cosmological implications of this new theoretical framework are studied. From the Hubble diagram …
Since the 1930s, astronomical observations have accumulated evidence that our understanding of the dynamics of galaxies and groups of galaxies is grossly incomplete: assuming the validity of Newton's law of gravity on astronomical scales, the observed mass (stored in stars and interstellar gas) of stellar systems can account only for roughly 10% of the dynamical (gravitating) mass required to explain the high velocities of stars in those systems. The standard approach to this "missing mass problem" has been the postulate of "dark matter", meaning an additional, electromagnetically dark, matter…
The discrepancy between observed virial and baryonic mass in galaxy clusters have lead to the missing mass problem. To resolve this, a new, non-baryonic matter field, known as dark matter has been invoked. However, till date no possible constituents of the dark matter components are known. This has led to various models, by modifying gravity at large distances to explain the missing mass problem. The modification to gravity appears very naturally when effective field theory on a lower dimensional manifold, embedded in a higher dimensional spacetime is considered. It has been shown that in a sc…
Not all those missing are lost: leveraging galaxy clustering in incomplete catalogs to unleash dark sirens cosmology
Max Planck Institute for Gravitational Physics（马克斯·普朗克引力物理学研究所）；University of Nevada, Las Vegas（内华达大学拉斯维加斯分校）；Institute for Astronomy, University of Edinburgh（爱丁堡大学天体物理研究所）；Università di Bologna（博洛尼亚大学）；INFN - Sezione di Bologna（意大利国家核物理研究所博洛尼部分部）
The history of the dark matter problem can be traced back to at least the 1930s, but it was not until the early 1970s that the issue of 'missing matter' was widely recognized as problematic. In the latter period, previously separate issues involving missing mass were brought together in a single anomaly. We argue that reference to a straightforward 'accumulation of evidence' alone is inadequate to comprehend this episode. Rather, the rise of cosmological research, the accompanying renewed interest in the theory of relativity and changes in the manpower division of astronomy in the 1960s are ke…
We demonstrate that the existence of a Noether symmetry in $f(R)$ theories of gravity gives rise to a further gravitational radius, besides the standard Schwarzschild one, determining the dynamics at galactic scales. By this feature, it is possible to explain the baryonic Tully-Fisher relation and the rotation curve of gas-rich galaxies without the dark matter hypothesis.
Up to now, Dark Energy evidences are based on the dynamics of the universe on very large scales, above 1 Gpc. Assuming it continues to behave like a cosmological constant $Λ$ on much smaller scales, I discuss its effects on the motion of non-relativistic test-particles in a weak gravitational field and I propose a way to detect evidences of $Λ\neq 0$ at the scale of about 1 Mpc: the main ingredient is the measurement of galaxy cluster masses.
We apply quantum gravitational results to spatially unbounded Friedmann universes and try to answer some questions related to dark energy, dark matter, inflation and the missing antimatter.
The recent discovery of cosmic repulsion represents a major challenge to standard gravity, adding an apparent missing energy problem to its still not yet adequately resolved missing mass one, while simultaneously requiring the current universe to be a very special, fine-tuned one. We suggest that the resolution of these difficulties lies not in the existence of more and more exotic gravitational sources, but rather in the lack of reliability of the extrapolation of standard gravity from its solar system origins to the altogether larger distance scales associated with cosmology. We suggest a ve…
