Testing the Cosmological Principle

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Sebastian von Hausegger


DKK 700,000




Visiting Fellowships at University of Oxford


This project targets the fundamental basis of our current model of our Universe: the Cosmological Principle. According to this principle the Universe obeys statistical homogeneity and isotropy. That means that, if averaged over sufficiently large scales, the distribution of matter looks the same everywhere and in every direction. My research aims to test whether this is true and, following recent hints of unexpectedly large bulk flows of matter, focuses on nailing down the peculiar motion of our Galaxy through space. This motion will be constrained by investigating effects on the Cosmic Microwave Background, galaxy number counts, and the so-called kinetic Sunyaev-Zeldovich effect.


The properties of space which mentioned in the previous paragraph are, in fact, only assumptions, which are yet to be tested in full detail. If data tells us that they are not justified, this would require a massive rethink of our current cosmological theory, including all its current mysteries. It is possible that the corresponding resolution also sheds light on concepts, such as dark energy and dark matter. In particular, distinction between phenomena in our cosmic neighbourhood and corresponding inference of global quantities should be ensured. It is intriguing that advances on cosmological scales highlight our very special place in the Universe.


Luckily we are blessed with a plethora of cosmological data which, if employed correctly, will be key in ‘Testing the Cosmological Principle’. A large part of my research will therefore be data analysis. I will employ advanced statistical methods to distill the small signals which are expected to reveal information about local kinematics and therefore might know about possible deviations from cosmic isotropy and homogeneity. In addition I will perform theoretical calculations of signatures one expects from a locally, or globally, ‘tilted’ cosmology – a mechanism of generating a large-scale bulk motion. In all steps and challenges I will be looking forward to exchange know-how with the many experts including my host in the Physics Department at the University of Oxford.

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