%0 Journal Article
%T Why do cosmological perturbations look classical to us?
%+ Laboratoire de Physique Théorique et Astroparticules (LPTA)
%A Kiefer, Claus
%A Polarski, David
%Z 12 pages, Revtex, invited contribution to a special issue of Advanced Science Letters, final version
%< avec comité de lecture
%Z 09-048
%@ 0976-397X
%J Advanced Science Letters
%I American Scientific Publishers
%V 2
%N 2
%P 164-173
%8 2009-06-04
%D 2009
%Z 0810.0087
%Z Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO]
%Z Physics [physics]/General Relativity and Quantum Cosmology [gr-qc]
%Z Physics [physics]/Quantum Physics [quant-ph]Journal articles
%X According to the inflationary scenario of cosmology, all structure in the Universe can be traced back to primordial fluctuations during an accelerated (inflationary) phase of the very early Universe. A conceptual problem arises due to the fact that the primordial fluctuations are quantum, while the standard scenario of structure formation deals with classical fluctuations. In this essay we present a concise summary of the physics describing the quantum-to-classical transition. We first discuss the observational indistinguishability between classical and quantum correlation functions in the closed system approach (pragmatic view). We then present the open system approach with environment-induced decoherence. We finally discuss the question of the fluctuations' entropy for which, in principle, the concrete mechanism leading to decoherence possesses observational relevance.
%G English
%L hal-00398336
%U https://hal.science/hal-00398336
%~ IN2P3
%~ LPTA
%~ CNRS
%~ UNIV-MONTP2
%~ UNIV-MONTPELLIER
%~ UM1-UM2