In 1950, a group of physicists met to discuss recent newspaper reports on sightings of UFO's (Unidentified Flying Objects). During this lunchtime conversation, Enrico Fermi, a Nobel Prize winner in physics, asked the question, "So, where are they?" -- by which he meant, "where are the aliens." His point was that, with so many stars in the Milky Way, it should be expected that the conditions for life would exist in many places in our galaxy -- not just on the Earth. If life exists, then evolution would be expected to lead to intelligent species and eventually to technological civilizations. Yet science has so far found no trace of alien civilizations, despite the considerable effort devoted to projects such as SETI (Search for Extraterrestrial Intelligence).

While alien civilizations are typically the prerogative of science fiction, there is nevertheless a serious scientific purpose to the search for evidence of other civilizations. If humanity is indeed a singular case, there must be an explanation as to why our star (the sun), our solar system and our planet are unique. |~Many theories have been proposed to explain the apparent lack of other life forms. Life, and especially intelligent life, may in fact be exceedingly rare, or such life exists and we have neither found it, been able to contact it, or we simply have not noticed it.| Each of these points of view has many different theories associated with it, making the "Fermi paradox" an active area of research and scientific thought, especially in the emerging field of astrobiology.