http://arxiv.org/PS_cache/arxiv/pdf/0712/0712.2865v1.pdf New Frontiers in Cosmology and Galaxy Formation: Challenges for the Future Authors: Richard Ellis (Caltech), Joseph Silk (Oxford) Comments: To appear in "Structure Formation in the Universe", ed. Chabrier, G., Cambridge University Press. High resolution version on this http URL Subjects: Astrophysics (astro-ph) (Abridged) Cosmology faces three distinct challenges in the next decade. (1) The dark sector, both dark matter and dark energy, dominates the Universe. Key questions include determining the nature of both. Improved observational probes are crucial. (2) Galaxy formation was initiated at around the epoch of reionization: we need to understand how and when as well as to develop probes of earlier epochs. (3) Our simple dark matter-driven picture of galaxy assembly is seemingly at odds with several observational results, including the presence of ULIRGS at high z, the `downsizing' signature, chemical signatures of alpha-element ratios and suggestions that merging may not be important in defining the Hubble sequence. Understanding the physical implications is a major challenge for theorists and refiniing the observational uncertainties a major goal for observers. The thing that interests me is the (what is the universe made of) question, and the finding or lack of of what is proposed.