Are We Missing E.T.'s Call?

The only problem is that SETI
astronomers tend to use our own technological capability as a yardstick
to estimate what the aliens should be capable of – and the current trend
suggests that the more advanced a civilization gets, the less we’d hear
from them. For instance, Drake pointed out that television
transmissions used to be sent out with 18 megawatts of power. “That was
one of the prime signs of our existence,” he said. But thanks to
advances in signal technology, those power levels have been reduced to 5
megawatts. Then you have to consider that more and more transmissions
are being directed downward to Earth from telecom satellites, instead of
upward from terrestrial transmitters. That could reduce the signature
of Earth’s radio emissions from millions of watts to mere watts of
reflected power. “What’s happening here is that the earth is growing
quiet,” Drake said. “If we are the model for the [intelligent] universe,
that’s bad news.”

SETI searchers would have to trust
that other civilizations would be sending out intentional signals –
using either old-fashioned radio or perhaps ultra-short pulses of light.
When astronomers look for light signals, in a relatively recent
strategy known as optical SETI, they have to assume that E.T. is
directing a powerful beacon at targets around the cosmos. Fortunately
for those astronomers, doing optical SETI can be about as inexpensive as
Project Ozma was 50 years ago. “Two thousand dollars and a smart
graduate student, and you can be in the SETI business,” Drake observed.

Astronomers
are working on more expensive strategies as well: One idea that’s been
around for quite a while calls for putting a radio observatory on the
far side of the moon, virtually the only place in the solar system that
is perpetually shielded from terrestrial transmissions. Another way-out
strategy would be to set up a monitoring station far from the sun –
maybe 500 to 1,000 times as far away as Earth. At that distance, the sun
could focus light waves (and radio waves) from cosmic frontiers like a
giant lens.

“We could well have an Internet for the
galaxy, based on gravitational lenses,” Drake said. Berkeley astronomer
Dan Wertheimer, one of the scientists behind the SETI @ home
alien-hunting screensaver program, said observers at such a
gravitational-lens observatory could “read the license plates on an
extrasolar planet.”

And if things get too quiet on
Earth, as Drake suspects, that might be just a temporary situation. The
deployment of space solar-power satellites would involve sending
gigawatts’ worth of power down to Earth, and some of that energy would
be reflected back into space. “If we go this route, the earth will
become visible again,” Drake said. But would that be a good thing? Would
we really want the aliens to know we exist, or should we lie low?
That’s a completely different story.”