Robert H. Gray
In 2016, Gray published an article in "Scientific American" about the Fermi paradox, which claims that if extraterrestrials existed, we would see signs of them on Earth, because they would certainly colonize the galaxy by interstellar travel. Gray argues that the Fermi paradox, named after Nobel Prize-winning physicist Enrico Fermi, does not accurately represent Fermi's views. Gray states that Fermi questioned the feasibility of interstellar travel, but did not say definitively whether or not he thought extraterrestrials exist.
Future of Humanity Institute
A recurring theme in FHI's research is the Fermi paradox, the surprising absence of observable alien civilizations. Robin Hanson has argued that there must be a "Great Filter" preventing space colonization to account for the paradox. That filter may lie in the past, if intelligence is much more rare than current biology would predict; or it may lie in the future, if existential risks are even larger than is currently recognized.