I learned physics at the Autonomous University of Barcelona, and astronomy on my own and through some amateur associations in Catalonia. I did my PhD in astrophysics at Princeton University, graduating in 1991 with a thesis on gravitational lensing by clusters of galaxies and large-scale structure. I was a postdoc at the Institute of Astronomy in Cambridge, and a Long-Term Member at the Institute for Advanced Study. I joined the University of Pennsylvania as a professor of astrophysics in 1996, and then moved to The Ohio State University in 2000. I have been back to Catalonia with an ICREA position since 2005, and I am at present doing research on astrophysics and cosmology at the Institut de Ciències del Cosmos at the University of Barcelona.
I enjoy searching for physical explanations of what we observe in the Universe. My interests range over the formation of galaxies and their large-scale distribution in space, dark matter and dark energy in the Universe, the intergalactic medium, the formation of massive black holes and the dynamics of nuclear regions of galaxies, and gravitational lensing as a probe to the nature of dark matter. Over the last few years I have focused on the large-scale distribution of intergalactic gas probed by spectroscopic surveys of quasars in which hydrogen and heavy elements are observed in absorption. This is revealing crucial clues on both the initial conditions of the Universe and the formation of galaxies. At present I am also looking at various techniques to inquire on the nature of dark matter, among them the observation of extremely magnified high-redshift stars close to the critical curves of clusters of galaxies acting as gravitational lenses, and the study of tidal streams of stars left by stellar systems orbiting the Milky Way galaxy.