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The expansion history of the universe with quantum gravity

Vejleder: Astrid Eichhorn


The Friedmann equations describe the evolution history of our universe, and how it expands as a function of time. As we follow that evolution backwards, we encounter the big-bang singularity, which indicates that the Friedmann equations are incomplete and need to be modified.

The aim of this thesis is to understand modifications of the Friedmann equations that remove the big-bang-singularity.

As first part of the thesis, the student will review the Friedmann equations and various expansion histories of the universe with various matter contents, such as radiation (i.e., relativistic particles) as well as dust, and review the big-bang-singularity.

As a second part, an upgrade of the Friedmann equations will be considered, in which the gravitational Newton constant is taken to be a function of the density of matter in the universe. It will be explored, which type of modifications are compatible with observational tests of cosmology in the late universe, while changing the evolution history of the early universe such that the Big-Bang-singularity is removed.

In particular, this second part of the thesis will make contact to current research, where bounce-cosmologies are considered as an alternative to Big-Bang-cosmologies and are motivated by quantum gravity. Here, the student will learn about the Planck-length, the scale of quantum gravity, to motivate when modifications of the Friedmann equations set in. Further, a comparison to the scales that are being probed by the Large Hadron Collider will be made, to understand how far the densities and energies that are reached in these particle collisions are from testing the conditions in the very early universe.

Institut for Fysik, Kemi og Farmaci Syddansk Universitet

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  • Odense M - DK-5230
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Sidst opdateret: 23.08.2021