Basic extrapolations suggest that if there are other spacefaring civilizations in the Milky Way, they could spread across the entire galaxy with surprising speed. Why, then, have we found no irrefutable evidence of aliens visiting Earth? Popular answers to this puzzle — that we are alone, that interstellar travel is impossible, that aliens are hiding from us — all rest on assumptions that verge on implausibility.
of this story at Slashdot.
Source:: Slashdot