Pondering the Fermi Paradox

The past two decades have witnessed an unprecedented increase in the amount and quality of observational data available to astronomers and cosmologists. Orbiting observatories such as the Hubble Space Telescope and the Wilkinson Microwave Anisotropy Probe (WMAP) have peered at the universe through a variety of windows in the electromagnetic spectrum. Ground-based projects such as the Sloan Digital Sky Survey (Adelman- McCarthy et al., 2008) and the 2dF Galaxy Redshift Survey (Colless et al., 2003) have mapped the distribution of galaxies in exquisite detail. Taken together, data from these and other projects have transformed our understanding of the large-scale structure of the universe, have steadily improved our knowledge of key cosmological parameters, and have provided compelling evidence in favor of a simple cosmological model (Spergel et al., 2009).