Aliens need a lot more time to find us
* 09:30 20 January 2007
"So, where is everybody?" Nobel laureate Enrico Fermi reportedly quipped to fellow physicists in 1950, when discussing why we haven't seen any signs of alien civilisations if, as many believe, our galaxy is teeming with life. Now, a maths model may have an answer to Fermi's paradox.
Rasmus Björk of the Niels Böhr Institute in Copenhagen, Denmark, has calculated that eight probes - travelling at a tenth of the speed of light and each capable of launching up to eight sub-probes - would take about 100,000 years to explore a region of space containing 40,000 stars. When Björk scaled up the search to include 260,000 such systems in our galaxy's habitable zone, the probes took almost 10 billion years - three-quarters the age of the universe - to explore just 0.4 per cent of the stars (http://arxiv.org/abs/astro-ph?papernum=0701238).
So, Björk's answer to the Fermi paradox: aliens haven't contacted us because they haven't had the time to find us yet.
He adds that the search could be optimised by visiting only those stars that harbour habitable planets, which could be identified by planet-finding missions such as NASA's Terrestrial Planet Finder. Björk is also "cautiously optimistic" about listening out for aliens with radio telescopes.