Image - Courtesy Pierre Mourier (CRAL)
Below the latest results from the ERC arthUs.
Space Is the Place. How to master spatial average properties of the Universe?
by Thomas Buchert (CRAL), Pierre Mourier (CRAL) & Xavier Roy (regular visitor of CRAL).
The question of how to define a cosmological model within General Relativity without symmetry assumptions or approximations can be approached by spatially averaging the scalar parts of Einstein’s equations. This yields general balance equations for average properties of the Universe. One open issue that we address here is whether the form and solutions of these equations depend on the way we split spacetime into spatial sections and a global cosmological time. We also discuss whether we can at all achieve this – given the generality of possible spacetime splits.
Our CQG Letter (Thomas Buchert et al. 2018 Class. Quantum Grav. 35 24LT02.) explores the general setting with a surprisingly simple answer, and CQG+ 28 November 2018 presents the authors.
Is the Cosmic Microwave Background Gaussian?
by Thomas Buchert (CRAL), Martin J. France (CRAL) & Frank Steiner (associated researcher of CRAL).
This challenging question touches on the initial conditions of the primordial Universe, on modeling assumptions, and statistical ensembles generating the Cosmic Microwave Background.
Our CQG paper (Thomas Buchert et al. 2017 Class. Quantum Grav. 34 094002) explores model-independent approaches to these challenges and CQG+ 18 April 2017 presents the authors.
Image above: The anisotropies of the cosmic microwave background, or CMB, as observed by ESA’s Planck mission. Date : 17 July 2018. Copyright : ESA/Planck Collaboration.
The Universe is inhomogeneous. Does it matter?
by Thomas Buchert (CRAL) et al.
Yes! The biggest problem in cosmology—the apparent acceleration of the expansion of the Universe and the nature of dark energy—has stimulated a debate about “backreaction”, namely the effect of inhomogeneities in matter and geometry on the average evolution of the Universe. Our recent paper (T. Buchert et al. 2015 Class. Quantum Grav. 32 215021) aims to close a chapter of that debate, to encourage exciting new research in the future and CQG+ 20 January 2016 presents the team.
Several conferences on these topics have occured in 2018, in which the arthUs team has presented its work:
- Inhomogeneous Cosmologies III, Kraków, PL, September 2018
- 2nd World Summit on Exploring the Dark Side of the Universe, Point-à-Pitre, FR, June 2018
- From inhomogeneous gravity to cosmological back-reaction: Theoretical opportunity? Observational evidence? Marseille, FR, May 2018