Structure formation in a preposterous universe

Matthias Steinmetz,
Astrophysikalisches Institut Potsdam (AIP)

Few topics in physical sciences have developed as rapidly as the field of cosmology and extragalactic astrophysics. Ten years ago, the principle parameters describing the structure, and thus the future development of our cosmos were largely unconstraint. The census of objects in the universe was largely limited to the present day epoch and to the immediate neighborhood of the Galaxy. Nowadays, we have entered the epoch of "precision cosmology", where cosmological parameters are determined at a level of a few per cent. The developing population of galactic objects is routinely traced throughout 95% of the age of the universe providing a detailed record of the changing structural and kinematical properties of galaxies. The resulting cosmological concordance model is capable in reproducing and testing an impressive array of cosmological observations such as the creation of light elements 1 sec after the big bang, the properties of the cosmic plasma 300 000 years after the big bang (as observed in the microwave background radiation), and the formation of large scale structures in the universe during the last couple of billion years.
Even some of the intricate details of the structure of our Galaxy and the origin of different galactic morphologies can be readily explained in the framework of the concordance model. The price for this success, however, is high: We are forced in positing the existence of dark matter and dark energy. 25% of the universe is in some sort of dark matter, for which particle physics provides at best educated guesses on its nature. Even more upsetting, 70% of the universe appears to be of mysterious dark energy, whose mere existence is already a challenge to the standard framework of particle physics.