Université de GenèveDépartement de Physique ThéoriqueCAP Genève






Cosmology is the study of the Universe as a whole. As an empirical science, cosmology involves the theoretical modelling of the Universe and its contents, as well as testing model predictions against precise astronomical observations.

Since Hubble's observations in 1929, the strong belief in a static Universe has been discredited and we know that the geometry of the Universe is expanding. Theoretically, this fact is well understood, since one of the solutions to Einstein's equations represents an expanding homogeneous and isotropic Universe. However, in 1998, observations of distant supernovae indicated that the picture of an expanding Universe was not complete. Using the luminosity distances of supernovae, scientists concluded that the Universe is currently in a phase of accelerated expansion. This surprising fact cannot be explained in a Universe filled only with matter and radiation. Indeed, the gravitational potential of matter and radiation can only slow down the expansion. Since 1998, other experiments have confirmed the accelerated expansion of the Universe, like the Cosmic Microwave Background.

Three main approaches are currently widely studied to explain this phenomenon. The first one postulates the existence of an exotic form of energy, called dark energy, that drives the acceleration with its anomalous negative pressure. The second one brings into question the homogeneity of our Universe, and the third one proposes modifications of General Relativity at cosmological scales.

Another big puzzle in our Universe is Dark Matter. Already in 1933, Zwicky noticed that the amount of visible matter inside the Coma Cluster was too small to explain the velocities of galaxies. Since then, Zwicky's results of missing matter have been confirmed by several observations, including the observations of the motion of stars within galaxies. Given the amount of visible matter and assuming that newtonian gravity is still valid at these scales, it is possible to show that the velocity of stars in the outer part of the galaxy is much larger than expected. In order to make theory and observations compatible, one postulates more matter than what we see, called for this reason dark matter.

Although dark energy and dark matter are two of the most pressing problems on the way to a coherent understanding of our Universe, these are not the only fields of intensive research. Our group is active in many areas of cosmology. Below is a list of the main topics and issues we are working on. Click on the links to see a short description of the topic and find our relevant contributions.


Département de Physique Théorique
Université de Genève
24, quai Ernest Ansermet
1211 Genève 4
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