Could there be anyone out there ? Vast distances between habitable planets could make communication with alien life an inviable concept. For years SETI has been scouring the skies for signs of radio signals from an intelligent extraterrestrial race, but despite its best efforts there has still been no sign that anyone else is out there. Given however that our galaxy spans over 100,000 light years it could be argued that there may simply be no intelligent civilizations close enough for us to pick up. Even receiving a signal from our nearest stellar neighbor, Alpha Centauri, would take four years. Recent advances in planet hunting suggest that there are an estimated 40 billion habitable planets in our galaxy, but that doesn't help if the distances between them are too large. "On average, you’d expect the civilizations to be separated by at least 1,000 light-years in the Milky Way," said astronomer Michael Garrett. "That’s a large distance, and for communication purposes you need to allow for twice the travel distance, so you’re talking about civilizations that have to be around for at least a few thousand years in order to have the opportunity to talk to each other." There is also the possibility that radio waves, being limited to the speed of light, may not be fit for communication over long distances and that a sufficiently advanced alien race might be using some other sophisticated communication system that we haven't even discovered yet. Picking up an alien civilization's radio signals may in fact be like finding a needle in a haystack with an extremely limited window of opportunity - the odds of this could be incalculably low.