The Possibilities of a Signal
These and similar arguments
have been extensively discussed in the SETI literature. However, rather than dwell on evolutions
likely products, allow me to argue the case for detecting intelligence by
pointing out that the universe offers many possibilities for providing us with
a signal - more possibilities than at first may be apparent.
First off, I would like to note
that the usual view of aliens is highly conservative. When we consider the cut of ETs jib, we generally incline to the
models offered to us by Hollywood.
Cinema aliens are highly anthropomorphic (as director Frank Capra once
observed, people are most interested in people) and not very diverse. Movie aliens are like movie cowboys: their
hats come in only two colors. There are
good aliens, such as those in Close Encounters of the Third Kind and
E.T. These are more than
anthropomorphic. They look like
children, and are clearly harmless.
Black-hatted aliens, on the other hand, such as those in Independence
Day, are modeled after our natural enemies: carnivores, snakes, insects,
etc. These fictional aliens, both good
and bad, populate our collective unconscious.
They are what we expect to be keying the transmitter at the other end of
a SETI signal. Their general properties
are as follows:
They are soft and squishy, protoplasmic, pulsing, oozing, and mortal.
They are an animal species, and are members of a society composed of a large number of individuals.
They have evolved via Darwinian evolution.
They are living on planets; indeed, somewhat Earth-like planets (and this is why SETI researchers become so excited at the discovery of extrasolar planets).
That may be what we
expect. But what is it that our search
technology can actually find? What we are looking for are narrow-band,
microwave signals - a type of emission that (as far as we know) is not produced
naturally. So the requirements for SETI
to succeed are (a) the existence of technology, i.e. a transmitter at the other
end, and (b) most probably a deliberately broadcast signal designed to get our
attention. This latter requirement
derives from the fact that advanced civilizations may be relatively radio
quiet, relying on low power (think of cellular phones) or highly directed
(optical) communications. Consequently,
they will not be leaking high-powered emissions into space. Furthermore, in order to inexpensively
deliver an easily detected signal at interstellar distances, they will need to
use reasonably large-sized transmitting antennas. Such antennas are highly directional (typical gains are 105 to
107 for terrestrial equipment).
The picture we generally have
of aliens, and one whose probability Professor DeVore has addressed, is hardly
either described or proscribed by these simple technical requirements. There are other possibilities. So I hope you will let me (at least
momentarily and in a spirit of general amity) to grant DeVores premise. Let us assume that high biological IQ is
rare. I will continue to maintain that
SETI could still find the universe rife with intelligence - with sentient
The argument requires letting
your imagination run free. Think in
terms of deep space, but also deep time.
It is worth keeping in mind that the number of stars in the visible universe
is ~1022, or comparable to the number of grains of sand on all the beaches of
Earth. Approximately 10% of these
resemble our sun. In addition, evidence
for planets around sun-like stars is growing.
At least 3-5% of the stars examined for extrasolar planets are found to
have them. This implies the existence
of billions of planetary systems in the Milky Way alone. (Within the visible universe, the number is
approximately 100 billion times larger.)
Finally, note that the universe is two to three times the age of
Earth. We are the new kids on the
It may be that the evolution of
intelligence is unlikely. In an
infinite universe, that wouldnt matter.
In a finite, but breathtakingly large universe - an old universe of 1022
stars - it probably doesnt matter.
Contributed by: Dr. Seth Shostak