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70 Modern Robotics

CONNECTIONS: WHY AREN’T THEY HERE?

While our space probes go out into the solar system and beyond,
should we expect to meet robot spacecraft from other worlds?
Since the mid-1900s, scientists and science fiction writers have
speculated about the likelihood and prevalence of intelligent civiliza-
tions in the universe. SETI (Search for Extraterrestrial Intelligence) has
attempted to detect radio signals from such civilizations, but so far
there are no confirmed signs that anyone is out there.
What is the real likelihood that we are not alone in the galaxy?
One approach to answering this question, taken by radio astronomer
Frank Drake, was to plug probabilities (such as the presence of suit-
able stars and Earth-like planets) into an equation, which seemed to
yield thousands of possible intelligent civilizations in the Milky Way
galaxy alone. But this brings up the “Fermi paradox,” first suggested
by the famous nuclear physicist Enrico Fermi: “If there are so many
civilizations out there, why has no one visited us?”
The usual answer is that the distances between stars are so
immense that even advanced civilizations would have to consume
most of their available resources to send starships to visit even nearby
stars. Perhaps civilizations do not last long enough to explore very
far—or they do not consider the effort worthwhile.
The possibility of building advanced, self-reproducing robots
changes the equation somewhat. If such robots can mine the
resources they need, build their own starships, and spread from
star system to star system, calculations suggest that such a robot
“swarm” should be able to spread through our galaxy in only a few
hundred thousand years. Shouldn’t humanity already have been vis-
ited by space robots?
Of course, there are far too many unknowns for us to be confi-
dent about such speculations. Perhaps the robots came and went
millions of years ago, after deciding that Earth was not that inter-
esting. Or perhaps there were no robots because such a mechani-
cal civilization would presumably have begun through the efforts
of flesh-and-blood roboticists. If paleontologist Peter Ward and
astronomer Donald Brownlee’s argument in their book Rare Earth
(2000) is correct, advanced intelligent life may be exceedingly rare.
It may be humans who will get to build the robots who ultimately
explore the galaxy!