Open Questions: Extraterrestrial Intelligence
See also: Exobiology --
Extrasolar planets --
Categorization and concept formation
Life exists on Earth. We're pretty sure of that. Whether there is intelligent
life on this planet is still an open question.
But let's assume, for the sake of discussion, that there are intelligent
life forms on Earth. Once such life forms come to
realize that the home planet is not unique and that there are at least
some, and possibly very numerous other planets and possible habitats
for life, then it's natural for them to ask three questions:
What is "intelligent" life, anyway? As a working definition we might take
it to mean a form of life that is capable of asking those questions. On
this definition, then, there is "intelligent" life on Earth.
- Does life exist elsewhere?
- If so, does intelligent life exist elsewhere?
- If there is intelligent life elsewhere, can we communicate with it?
Another definition, however, would require of intelligent life the ability
to communicate with other intelligent life. In this more
restrictive sense (at least) the question of the existence of intelligent
life on Earth is still open.
Naturally, then, most of the focus has been on the question of the
existence of extraterrestrial intelligent life.
Now we come to an interesting paradox. On one hand, life in some form or
other, however primitive, is a prerequisite for intelligent life.
And intelligent life is probably a whole lot scarcer than life in any
But on the other hand, with the current state of our technology, it
might be easier to find signs of intelligent life before we find signs
of any other (except perhaps within our own solar system). The reason,
obviously, is that we would expect "intelligent" life to have sufficient
technology, at least as advanced as ours, to be able to send out signals
(deliberately or otherwise) that indicate it exists. Most likely, such
signals would use a part of the electromagnetic spectrum, especially
at what we call "radio" frequencies. But other parts of the spectrum,
such as what we call "optical" might also, or instead, be used. Or
perhaps even more exotic techniques, such as neutrino signals.
Let's not forget that our first question was whether any life at all exists
elsewhere. It's easy to lose sight of that, because it may be easier to
answer the following question as to whether intelligent life exists
elsewhere. This is because, except for planets (and some of their
satellites) in our own Solar System, it could be a rather long time
before we are able to detect the existence of rudimentary life forms
elsewhere. But intelligent life should be much easier to detect even
at interstellar distances, even if we can't actually "communicate"
Open Directory Project: Extraterrestrial Life
- Categorized and annotated links. A version of this
list is at
Google, with entries sorted in "page rank" order. May also be
- Categorized site directory. Entries usually include
SETI SuperStar Award Winning Websites
- List of SETI Web sites that have been selected monthly
since May 1999 for special merit by the
Sites with general resources
Yahoo News Full Coverage: Search for Extraterrestrial Life
- Links to recent news stories from various sources. Also includes
links to sites dealing with the search for extraterrestrial life.
- "The SETI Institute serves as an institutional home for
scientific and educational projects relevant to the nature,
distribution, and prevalence of life in the universe." Site contents
bibliography, and general SETI information.
- Cooperative distributed computing project to assist in the
search for extraterrestrial intelligence.
Sky and Telescope's SETI Section
- Contains news and background articles on SETI by varions
- Articles and news related to SETI from a variety of sources.
A WebSeed site.
The Planetary Society: SETI Page
- General news and information on SETI, with emphasis on projects
sponsored by The Planetary
Society. Has good history and overview articles.
There is also information on the Society's
SETI Optical Telescope.
Jodrell Bank Observatory SETI Research
- Pages that describe the Observatory's SETI research. They
history of SETI,
common questions and answers, and an explanation of the
The SETI League
- Web site of an "international grass-roots organization
dedicated to privatizing the electromagnetic Search for
Extra-Terrestrial Intelligence." The site includes general
information on the organization and SETI. There is an
archive of publications, such as newsletters, journals,
press releases, and photos. The organization also selects
other SETI sites for a special award.
Princeton Optical SETI Project
- "The Optical SETI (OSETI) project at Princeton University,
working in collaboration with Harvard University, searches
nearby stars in an effort to detect brief, high-powered laser
pulses that might signify the existence of extraterrestrial life
in other solar systems."
Surveys, overviews, tutorials
- Article from
SETI Institute/Space.com articles
- A series of articles about SETI and (sometimes distantly)
related subjects, published weekly since Nopvember 2000 by the
SETI Institute and
The most relevant articles provide excellent information on
astrobiology and SETI..
Astronomy - SETI
- Explanation of Drake's equation.
Are We Alone?
- Special feature story from ABC News.
The Search for Extraterrestrial Life
- Part of the SEDS
site. Contains overview information and external links.
The eerie silence
- May 2010 article from
"Half a century after it began, the quest to find life
elsewhere in the universe has drawn an almost total blank.
Paul Davies calls for the search to be relaunched by examining
not just radio signals but all physical and astronomical anomalies."
The search for astroengineers
- April 2008 article from
Physics World, by
"Having so far failed to find evidence for extraterrestrial
civilizations by searching for their radio transmissions, some
physicists think it is worth scouring the sky for signs of their
astronomical construction work."
'Idle' machines look for ET
- July 1998 news article from
Physics World, about
the SETI@home project to use the power of networked home
computers to analyze radio telescope data for the presense
of possible signals of extraterrestrial intelligence.
The Search for Extraterrestrial Intelligence
- Extensive January 1997 article from Scientific American
online, by Carl Sagan and Frank Drake.
"There can be little doubt that civilizations more advanced than the
earth's exist elsewhere in the universe. The probabilities involved
in locating one of them call for a substantial effort."
- Using Lasers to Detect E. T.
Astronomy, September 2002, pp. 44-49
- There's no good reason an advanced extraterrestrial civilization
would use radio frequencies to signal its presence instead of
infrared or visible light. Within just the last few years searches
have begun for such signals -- which might be generated by laser
pulses that could be (briefly) a million times brighter than a
Where Are They?
Scientific American, July 2000, pp. 38-43
- If advanced civilizations exist elsewhere in the galaxy, they
should develop the ability so spread throughout the galaxy in only
a few million years. As Enrico Fermi first noted, this means we
should have seen more evidence of such civilizations than we have.
- Is There Life Elsewhere in the Universe?
Jill C. Tarter; Christopher F. Chyba
Scientific American, December 1999, pp. 118-123
- The dedicated search for signs of extraterrestrial life
and intelligence has barely begun. But the search, by a variety
of means, is due for rapid acceleration.
- Are We Alone?
David J. Eicher
Astronomy, November 1999, pp. 60-63
- Several researchers who have studied the issues involved in
SETI discuss opinions, both optimistic and pessimistic, on the
likelihood of discovering extraterrestrial intelligence.
- Who's Out There?
Discover, April 1999, pp. 64-70
- New techniques and technology continue to be deployed in
the search for extraterrestial intelligence. One of the latest
involves using home computers to process data.
- Stephen Webb – Where Is Everybody? Fifty Solutions to
the Fermi Paradox and the Problem of Extraterrestrial Life
Copernicus Books, 2002
- The title alludes to Fermi's question – if intelligent
extraterrestrial life exists in our galaxy, why haven't they
shown up yet in an obvious way? Webb considers 50 possible
answers in three different categories. Along the way, he
explains a lot of exobiology. Just so you know what you're
getting with this book, Webb's own conclusion is that
the conditions for life on Earth are so special that there are
no intelligent extraterrestrials.
Copyright © 2002 by Charles Daney, All Rights Reserved