We see aliens in the movies all the time. We do not yet have any evidence for the existence of extraterrestrial intelligence. And yet, for most scientists, it is a distinct possibility in the universe. In fact, two developments in the 19th century - one in theory and one in technique - made the idea of extraterrestrial intelligence a scientific one. In this episode of Science ka Adda we look at those developments and ponder on the possibility of aliens on other worlds. For more videos in the series, please visit sciencekaadda.com or join us on Facebook at facebook.com/ScienceKaAdda .