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.
My guess is that the numbers might be different however. An alien civilization that could send out probes at one tenth the speed of light would probably be smart enough to create self-replicating probes, in order to generate thousands or millions of probes over time. This might bring the numbers down significantly -- although perhaps still not enough.