Knowing what the Universe is precisely made of, and in which proportions, allows not only to determine its age but also to reconstruct the history, to predict its past and future. In fact in the attempt to solve this question cosmologists have made two of the most promising discoveries in the history of modern physics: the existence of dark matter and dark energy.
While dark matter is unavoidable to explain at the same time the angular fluctuations of the cosmic microwave background and the formation and the properties of galaxies, dark energy has been originally invoked to account for the observed recent acceleration of the cosmic expansion. The so-called concordance model of cosmology assumes that this dark energy is in fact the cosmological constant once introduced by Einstein himself as an attempt to incorporate Mach’s principle within general relativity. However, the usual interpretation of the cosmological constant in terms of quantum vacuum fluctuations is in disagreement with observed value by a few dozens orders of magnitude! Furthermore, as the vacuum energy is assumed constant everywhere at all times, it is hard to explain how it became dominant only a few billion years ago. This would mean that we live in a very particular, and even privileged, epoch of cosmic history… Is this an extraordinary coincidence? Yet this anthropic consideration is quite deceiving for scientists.
To overcome these difficulties, the authors, Jean-Michel Alimi and André Füzfa, have proposed the AWE Hypothesis (« Abnormally Weighting Energy ») in which the dark sector of cosmic matter violates the equivalence principle on cosmological scales. This principle, as well introduced by Einstein, assumes that all kinds of energies produce and undergo the same form of gravity. This principle is extremely well tested (to a part out of a thousand billion) in laboratories, i.e. at local scales, in contrast what would happen if violation of the equivalence principle would be scale-dependant. In other words, what would happen if the equivalence principle was rigorously verified at local scales, where dark matter and dark energy are present in tiny amount, but is violated on cosmological scales where dark matter and dark energy are dominant? The authors have precisely shown that this could naturally happen if some particles, those of dark matter for instance, do not couple to gravitation in the same way as ordinary matter. These particles would therefore see gravitational fields with a gravitational strength different from ordinary matter. The authors have answered these questions by showing how at a given scale the gravitational strength becomes dependent on dark matter concentration…
If the amount of dark matter at sub-galactic scales is negligible, so is the amplitude of this effect. This is not the case on cosmological scales where dark matter dominates the energy content of the Universe. The team has shown that over such cosmic distances, ordinary matter has experienced a stronger cosmic expansion, as its own gravitational coupling strength has been adapting to the dark matter domination. This change in the matter gravitational coupling results in an accelerating cosmic expansion until equilibrium is reached such that the gravitational coupling on cosmological scales stabilizes at a value which differs from the one measured in our Solar system. The resulting dark energy mechanism exhibits key features which appear very promising. (i) First, it does not require the existence of negative pressures such as in the case of the cosmological constant or other proposed models like quintessence. (ii) It allows explaining naturally the cosmic coincidence as result of the stabilization mechanism of the gravitational constant during the matter-dominated era. (iii) It fairly accounts for the Hubble diagram of type Ia supernovae by predicting independently the amount of ordinary matter and dark matter as obtained by the detailed analysis of cosmic microwave background anisotropies. This suggests an explanation to the remarkable adequacy of the concordance model while predicting an age of the Universe which is compatible with existing observations. Finally, (iv) in the future this mechanism leads to a decelerated cosmic expansion described by the well-known Einstein-de Sitter cosmological model. Most important is the AWE hypothesis allows reducing dark energy as a new property of gravitation: the anomalous gravity of dark matter.
Jean-Michel Alimi | alfa
SF State astronomer searches for signs of life on Wolf 1061 exoplanet
20.01.2017 | San Francisco State University
Molecule flash mob
19.01.2017 | Technische Universität Wien
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences