It ranks among the most
enduring mysteries of the cosmos. Physicists call it
the Fermi paradox after the Italian Nobel laureate
Enrico Fermi, who, in 1950, pointed out the glaring
conflict between predictions that life was elsewhere
in the universe - and the conspicuous lack of aliens
who have come to visit.
Now a Danish
researcher believes he may have solved the 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 civilization
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.
Bork 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. His study is reported in New
Scientist today.
Like humans, alien
civilizations could shorten the time to find
extra-terrestrials by picking up television and
radio broadcasts that might leak from colonized
planets. "Even then, unless they can develop an
exotic form of transport that gets them across the
galaxy in two weeks it's still going to take
millions of years to find us," said Mr. Bjork.
"There are so many stars in the galaxy that probably
life could exist elsewhere, but will we ever get in
contact with them? Not in our lifetime," he added.
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