Carl%20Sagan%20-%20The%20Demon%20Haunted%20World

The Dragon in My Garage
answer to what a pulsar is has to be something mighty strange. It
isn't an extraterrestrial civilization. It's something else: but a
something else that opens our eyes and our minds and indicates
unguessed possibilities in Nature. Anthony Hewish won the Nobel
Prize in physics for the discovery of pulsars.
The original Ozma experiment (the first intentional radio
search for extraterrestrial intelligence), the Harvard University/
Planetary Society META (Megachannel Extraterrestrial Assay)
programme, the Ohio State University search, the SERENDIP
Project of the University of California, Berkeley, and many other
groups have all detected anomalous signals from space that make
the observer's heart palpitate a little. We think for a moment that
we've picked up a genuine signal of intelligent origin from far
beyond our solar system. In reality, we have not the foggiest idea
what it is, because the signal does not repeat. A few minutes later,
or the next day, or years later you turn the same telescope to the
same spot in the sky with the same frequency, bandpass, polarization,
and everything else, and you don't hear a thing. You don't
deduce, much less announce, aliens. It may have been a statistically
inevitable electronic surge, or a malfunction in the detection
system, or a spacecraft (from Earth), or a military aircraft flying
by and broadcasting on channels that are supposed to be reserved
for radio astronomy. Maybe it's even a garage door opener down
the street or a radio station a hundred kilometres away. There are
many possibilities. You must systematically check out all the
alternatives, and see which ones can be eliminated. You don't
declare that aliens have been found when your only evidence is an
enigmatic non-repeating signal.
And if the signal did repeat, would you then announce it to the
press and the public? You would not. Maybe someone's hoaxing
you. Maybe it's something you haven't been smart enough to
figure out that's happening to your detection system. Maybe it's
some previously unrecognized astrophysical source. Instead, you
would call scientists at other radio observatories and inform them
that at this particular spot in the sky, at this frequency and
bandpass and all the rest, you seem to be getting something funny.
Could they please see if they can confirm? Only if several
independent observers - all of them fully aware of the complexity
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