As a life-long science, astronomy, and science fiction nerd, I've looked up into the skies and wondered not if there's life out there, but where.
In the early 80s, when I was about 11 or 12, I was really worried about the possibility of a nuclear war between the US and the Soviet Union, and after watching The Day The Earth Stood Still on my friend's Betamax player, I hoped that we would have a similar extra terrestrial intervention which would force humanity to stop fighting among ourselves.
Two decades later, we still haven't been visited by V'Ger, and as far as I know, there aren't a lot of people building models of Devil's Tower out of mashed potatoes. Personally, I don't believe we're alone in the universe (man, what myopic arrogance to think that we are) but people who are much smarter than me have been asking for a long time why, if we aren't alone, haven't we run into the Vogons yet?
The question was originally posed by Enrico Fermi, and has become known as the Fermi Paradox:
The extreme age of the universe and its vast number of stars suggest that extraterrestrial life should be common. Considering this with colleagues over lunch in 1950, the physicist Enrico Fermi is said to have asked: "Where are they?" Fermi questioned why, if a multitude of advanced extraterrestrial civilizations exist in the Milky Way galaxy, evidence such as probes, spacecraft or radio transmissions has not been found. The simple question "Where are they?" (alternatively, "Where is everybody?") is possibly apocryphal, but Fermi is widely credited with simplifying and clarifying the problem of the probability of extraterrestrial life.
A Danish researcher has come up with an interesting answer (if not a complete solution) to the Fermi Paradox:
Extra-terrestrials have yet to find us because they haven't had enough time to look.
Using a computer simulation of our own galaxy, the Milky Way, Rasmus Bjork, a physicist at the Niels Bohr institute in Copenhagen, proposed that a single civilisation might build eight intergalactic probes and launch them on missions to search for life. Once on their way each probe would send out eight more mini-probes, which would head for the nearest stars and look for habitable planets.
Mr Bjork confined the probes to search only solar systems in what is called the "galactic habitable zone" of the Milky Way, where solar systems are close enough to the centre to have the right elements necessary to form rocky, life-sustaining planets, but are far enough out to avoid being struck by asteroids, seared by stars or frazzled by bursts of radiation.
He found that even if the alien ships could hurtle through space at a tenth of the speed of light, or 30,000km a second, - Nasa's current Cassini mission to Saturn is plodding along at 32km a second - it would take 10bn years, roughly half the age of the universe, to explore just 4% of the galaxy.
Of course, there are cynics (occasionally I count myself among them) who say that we're just not interesting enough for a species who has achieved advanced space exploration to bother with, but that's such a gloomy outlook, I'll trade Human Behavior for Bjork on this one.