Speaker
Alain Blanchard
(IRAP)
Description
The acceleration of the expansion of the universe is now a well demonstrated feature of the universe which is almost impossible to bypassed. This leads to a very surprising question: why is gravity repulsive on large scales. By now, it is fair to say that we have no hint about the very reason for the origin of this phenomena (named hereafter dark energy) which can be regarded as one of the major surprises in modern physics. Tightening down the properties of dark energy is therefore a major objective of modern science in order to clarify its very nature. The simplest model of dark energy is a cosmological constant, as introduced by Einstein, equivalent to a (quantum) vacuum contribution to the energy budget of the universe. Alternative options are on one side the existence of a scalar field minimally coupled, named quintessence or with more complexity and on the other side the possibility that gravity is actually not driven by general relativity (GR) but by some modified gravity, which behaves like GR on small scales, but would be different on large scale. Possible test of such theories relies mainly on the behavior of gravity on large scales, beyond galactic scales. These scales are precisely the target of ongoing projects dedicated to dark energy investigation like the ESA space mission EUCLID. Several probes used in combination will allow to constrain dark energy properties with a high accuracy, allowing to test the theory of general relativity on cosmological scales.
Primary author
Alain Blanchard
(IRAP)
