Physical Cosmology

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  • Clusters of Galaxies


    Clusters of galaxies are the largest overdense structures in the Universe. Their formation and evolution is tightly connected to the expansion history and the growth of large scale structures in the Universe. This connection makes them exquisite probes for cosmological models. more

  • Cosmic Microwave Background


    The cosmic microwave background radiation was formed when the Universe was only about 300,000 years old, by effect of the decoupling of photons and electrons in the primordial plasma. This radiation has a nearly perfect black-body spectrum, with small anisotropies of order 10^-5 due to the local fluctuations at last scattering. In our group more

  • Cosmic Voids


    The dominant volume fraction of the Universe consists of relatively empty space, so-called cosmic voids. This is a simple consequence of gravitational clustering, which always acts to enhance over-dense structures via collapse, while under-densities are depleted and expand. more

  • Dark Energy


    Dark energy is the most abundant and yet most mysterious substance in the Universe. The existence of dark energy can be inferred by its effects on the expansion rate of the Universe and on the growth of cosmic structures, but its fundamental nature is still completely unknown. more

  • Large Scale Structure


    The large scale structure in the Universe evolved from the early linear density field. For this reason it carries the signature of early-universe processes like the initial thermal properties of the dark matter field or the impact of early dark energy onto the geometry of the Universe, as well as the characteristics of late-time, non-linear mechanisms like the collapse of overdensities under gravity into large scale structure. more

  • Machine Learning


    Astronomy and cosmology have firmly entered the data rich regime. We measure photometric properties of more than hundreds of millions of galaxies and stars. Machine learning is a data mining approach to make sense of this data flood, and has found many applications in cosmology, from the measurements of photometric redshifts, to the distinguishing between stars and galaxies. more

  • Modified Gravity


    The standard approach to modelling the late time acceleration of the Universe is to introduce a dark energy component and arrange its properties such that it dominates at late times and violates the strong energy condition. However, an alternative approach to describing the current epoch is to postulate that at cosmological distance scales, gravity deviates from its standard General Relativistic description. more