Dr. Adrian Kent is Reader in Quantum Physics at DAMTP, University of Cambridge and Associate Member at Perimeter Institute for Theoretical Physics, Waterloo, Ontario. He speculates that the answer to the Fermi Paradox might be that there is competition for resources on a cosmic scale. Advanced species, for example, might want to exploit other planets for their own purposes. That would give them a powerful disincentive to avoid interaction. See Is ET Avoiding Us Out of a Fear of Human Galactic Conquest? Mark Buchanan. io9. April 10, 2011.