Reginald Smith from the Bouchet-Franklin Institute in Rochester, New York has written a paper which claims that every civilization in the Milky Way stops broadcasting EM after 1000 years. Based on this assumption he shows that it is reasonable that our galaxy has multiple sentient species who never interact with each other. This assumption seems very weak to me. Why would every single species stop communicating by radio? He also has an implicit assumption that colonization is rare or non-existent.
The real answer to the Fermi Paradox is much simpler: the rate of evolution of sentient species is less than 1.0 per galaxy per 13 billion years. We are the first and only intelligent species in the Milky Way, the odds that another will evolve before we have colonized the galaxy is nearly zero. This theory perfectly fits the observed facts.