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Speaker |
Beyer, Florian |
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Talk Title |
The cosmic no-hair conjecture: A study of the Nariai solutions |
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Abstract |
The standard model of cosmology is tremendously successful for describing current cosmological observations. One of its keystones is the notion of inflation. A priori, one can believe that the understanding of the post-inflationary universe would require significant knowledge of the properties of the pre-inflationary cosmos. However, Hawking et al. have conjectured that all inflationary solutions of Einstein's field equations under certain assumptions, irrespective of the pre-inflationary conditions, approach the same inflationary solution asymptotically, namely the de-Sitter solution. This motivates the name "cosmic no-hair" conjecture which was chosen in analogy to the no-hair properties of black hole solutions. Since, according to this picture, the inflationary universe "loses its memory" about its pre-inflationary properties, this idea would allow us to refrain from speculating about the physics at the earliest times of the cosmos and the "initial conditions" at the big bang. This would be so at least for the qualitative description of the present universe. However, although there is certain support for the cosmic no-hair conjecture, it is up to now not clear under which conditions it really holds. The complexity of Einstein's field equations makes the analytical and numerical analysis very difficult. In this talk, I review the relevant background and then turn to a particular setting given by the so-called Nariai solutions. These solutions show quite unusual asymptotics not consistent with the cosmic no-hair picture. Our main task is to characterize the asymptotics of perturbations of these solutions in order to understand if the cosmic no-hair picture is really generic. In the class of spatially homogeneous perturbations, I discuss this problem analytically. In the spatially inhomogeneous class of Gowdy perturbations, I present numerical evidence for the genericity of the cosmic no-hair picture. |
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