PTINov 24, 2017 08:02:52 IST
Dark matter and dark energy may not actually exist, according to a study which suggests that accelerating expansion of the universe and the movement of the stars in the galaxies can be explained without these concepts.
For close to a century, researchers have hypothesised that the universe contains more matter than can be directly observed, known as "dark matter". They have also posited the existence of a "dark energy" that is more powerful than gravitational attraction. These two hypotheses, it has been argued, accounts for the movement of stars in galaxies and for the accelerating expansion of the universe respectively. However, according to a researcher at the University of Geneva (UNIGE) in Switzerland, these concepts may be no longer valid: the phenomena they are supposed to describe can be demonstrated without them.
The research, published in The Astrophysical Journal, exploits a new theoretical model based on the scale invariance of the empty space, potentially solving two of astronomy's greatest mysteries. The way we represent the universe and its history is described by Einstein's equations of general relativity, Newton's universal gravitation and quantum mechanics. The model-consensus at present is that of a Big Bang followed by an expansion.
"In this model, there is a starting hypothesis that has not been taken into account, in my opinion," said Andre Maeder, professor in UNIGE's Faculty of Science.
"By that, I mean the scale invariance of the empty space; in other words, the empty space and its properties do not change following a dilatation or contraction," said Maeder. The empty space plays a primordial role in Einstein's equations as it operates in a quantity known as a "cosmological constant", and the resulting universe model depends on it.
Based on this hypothesis, Maeder is now re-examining the model of the universe, pointing out that the scale invariance of the empty space is also present in the fundamental theory of electromagnetism. When Maeder carried out cosmological tests on his new model, he found that it matched the observations. He also found that the model predicts the accelerated expansion of the universe without having to factor in any particle or dark energy.
In short, it appears that dark energy may not actually exist since the acceleration of the expansion is contained in the equations of the physics, researchers said.
In a second stage, Maeder focused on Newton's law, a specific instance of the equations of general relativity. The law is also slightly modified when the model incorporates Maeder's new hypothesis. It contains a very small outward acceleration term, which is particularly significant at low densities. This amended law, when applied to clusters of galaxies, leads to masses of clusters in line with that of visible matter: this means that no dark matter is needed to explain the high speeds of the galaxies in the clusters.
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