On Communication with Extraterrestrials
Sir Frederick
ScienceWeek http://scienceweek.com
The following points are made by Woodruff T. Sullivan III (Nature
2004 431:27):
1) Although the Search for Extraterrestrial Intelligence (SETI)
has yet to detect a signal, the efforts continue because so
little of the possible parameter space has been searched so far.
These projects have almost all followed the dominant paradigm --
launched 45 years ago by Cocconi and Morrison(1) -- of using
radio telescopes to look for signs of extraterrestrial life. This
focus on electromagnetic waves (primarily at radio wavelengths,
but also at optical ones) was based on various arguments for
their efficiency as a means of interstellar communication.
However, Rose and Wright(2) have made the case that if speedy
delivery is not required, long messages are in fact more
efficiently sent in the form of material objects -- effectively
messages in a bottle. Although the suggestion itself is not
new(3,4), it had never before been backed up by quantitative
analysis.
2) A fundamental problem in searching for extraterrestrial
intelligence is to guess the communications set-up of the
extraterrestrials who might be trying to contact us. In which
direction should we look for their transmitter? At which
frequencies? How might the message be coded? How often is it
broadcast? (For this discussion I am assuming that the signals
are intentional, setting aside the a priori equally likely
possibility that the first signal found could be merely leakage
arising from their normal activities.) Conventional wisdom holds
that they would set up a beam of electromagnetic waves, just as
we could do with, for example, the 305-meter Arecibo radio
telescope in Puerto Rico, Earth's most powerful radio
transmitter, or a pulsed laser on the 10-meter Keck optical
telescope in Hawaii. Rose and Wright(2) conclude, however, that
the better choice would be to send packages laced with
information.
3) Unless the messages are short or the extraterrestrials are
nearby, this "write" strategy requires less energy per bit of
transmitted information than the "radiate" strategy does. Cone-
shaped beams of radiation necessarily grow in size as they travel
outwards, meaning that the great majority of the energy is
wasted, even if some of it hits the intended target. A package,
on the other hand, is not "diluted" as it travels across space,
presuming that it's correctly aimed at its desired destination.
For short messages, however, electromagnetic waves win out
because of the overheads involved in launching, shielding and
then decelerating a package, no matter how small it is. For a
two-way conversation with extraterrestrials, the light-speed of
electromagnetic waves is far superior.
4) As an example of a large message, consider all of the written
and electronic information now existing on Earth: it's
estimated(5) to amount to about one exabyte (10^(18) bytes). Rose
and Wright(2) calculate that, using scanning tunnelling
microscopy, these bits could be inscribed (in nanometer squares)
within one gram of material! But this precious package would
still require a cocoon of 10,000 kilograms to accelerate it from
our planet to a speed of 0.1% of the speed of light, protect it
from radiation damage along a 10,000-light-year route, and then
decelerate it upon arrival.
References:
1. Cocconi, G. & Morrison, P. Nature 184, 844-846 (1959)
2. Rose, C. & Wright, G. Nature 431, 47-49 (2004)
3. Bracewell, R. Nature 187, 670-671 (1960)
4. Papagiannis, M. Q. J. R. Astron. Soc. 19, 277-281 (1978)
5. Murphy, C. Atlantic 277, No. 5, 20-22 (1996)
Nature http://www.nature.com/nature
--------------------------------
Related Material:
ASTROBIOLOGY: ON INTELLIGENT LIFE IN THE UNIVERSE
The following points are made by J. Cohen and I. Stewart ((Nature
22 Feb 01 409:1119):
1) The authors point out that it is possible to imagine the
existence of forms of life very different from those found on
Earth, occupying habitats that are unsuitable for our kind of
life. Some of those aliens might be technological, because
technology is an autocatalytic process, and it follows that some
aliens might possess technology well in advance of our own,
including interstellar transportation. So much is clear, but this
train of logic begs the obvious question of where these
intelligent non-humanoid aliens might be.
2) The authors point out that the subject area of this discussion
is often called "astrobiology", although in science fiction
circles (where the topic has arguably been thought through more
carefully than it has been in academic circles) the term
"xenobiology" is favored. The authors suggest the difference is
significant: Astrobiology is a mixture of astronomy and biology,
and the tendency is to assume that the field must be assembled
from contemporary astronomy and biology; in contrast, xenobiology
is the biology of the strange, and the name inevitably involves
the idea of extending contemporary biology into new and alien
realms.
3) The authors ask: Upon what science should xenobiology be
based? The authors suggest that the history of science indicates
that any discussion of alien life will be misleading if it is
based on the presumption that contemporary science is the
ultimate in human understanding. Consider the position of science
a century ago. We believed then that we inhabited a newtonian
clockwork Universe with absolute space and absolute time; that
time was independent of space; that both were of infinite extent;
and that the Universe had always existed, always would exist, and
was essentially static. We knew about the biological cell, but we
had a strong feeling that life possessed properties that could
not be reduced to conventional physics; we had barely begun to
appreciate the role of natural selection in evolution; and we had
no idea about genetics beyond mendelian numerical patterns. Our
technology was equally primitive: cars were inferior to the
horse, and there was no radio, television, computers,
biotechnology or mobile phones. Space travel was the stuff of
fantasy. If the past is any guide, then almost everything we now
think we know will be substantially qualified or proven wrong
within the next 25 years, let alone another century. Biology, in
particular, will not persist in its current primitive form. At
present, biology is at a stage roughly analogous to physics when
Newton (1642-1727) discovered his law of gravity. "There is an
awfully long way to go."
4) The authors point out that evolution on Earth has been in
progress for at least 3.8 billion years. "This is deep time --too
deep for scenarios expressed in human terms to make much sense. A
hundred years is the blink of an eye compared with the time that
humans have existed on Earth. The lifespan of the human race is
similarly short when compared with the time that life has existed
on Earth. It is ridiculous to imagine that somehow, in a single
century of human development, we have suddenly worked out the
truth about life. After all, we do not really understand how a
light switch works at a fundamental level, let alone a
mitochondrion."
Nature http://www.nature.com/nature
--------------------------------
Related Material:
PROSPECTS FOR THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE
Notes by ScienceWeek:
The conjured image is poignant: intelligent life sprinkled
throughout our Galaxy, each sprinkle separated from the others by
1000 light years, each sprinkle searching for the others with
radio transmitters and receivers, small robotic spacecraft sent
beeping into empty space between the stars, the beeping like a
faint bleating in the dark as the sprinkles search for each
other. Of course, the conjured image may be wrong: there may be
intelligent life dense in the Galaxy; or we may be alone. It does
not matter. For the human species on this planet Earth, the quest
is part of our destiny, part of what we do as a species, and it
will go on as long as we remain civilized.
J.C. Tarter and C.F. Chyba (SETI Institute, US) present a review
of current and future efforts in the search for extraterrestrial
intelligence, the authors making the following points:
1) During the past 40 years, researchers have conducted searches
for radio signals from an extraterrestrial technology, sent
spacecraft to all but one of the planets in our Solar System, and
expanded our knowledge of the conditions in which living systems
can survive. The public perception is that we have looked
extensively for signs of life elsewhere. But in reality, we have
hardly begun to search. Assuming our current, comparatively
robust space program continues, by 2050 we may finally know
whether there is, or ever was, life elsewhere in our Solar
System. At a minimum, we will have thoroughly explored the most
likely candidates, a task not yet accomplished. We will have
discovered whether life exists on Jupiter's moon Europa, or on
Mars. And we will have undertaken the systematic exobiological
exploration of planetary systems around other stars, seeking
traces of life in the spectra of planetary atmospheres. These
surveys will be complemented by expanded searches for intelligent
signals.
2) The authors point out that although the current language is
that of a "search for extraterrestrial intelligence" (SETI), what
is being sought is evidence of extraterrestrial technologies.
Until now, researchers have concentrated on only one specific
technology -- radio transmissions at wavelengths with weak
natural backgrounds and little absorption. No verified evidence
of a distant technology has been found, but the null result may
have more to do with limitations in range and sensitivity than
with actual lack of civilization. The most distant star probed
directly is still less than 1 percent of the distance across our
Galaxy.
3) The authors conclude: "If by 2050 we have found no evidence of
an extraterrestrial technology, it may be because technical
intelligence almost never evolves, or because technical
civilizations rapidly bring about their own destruction, or
because we have not yet conducted an adequate search using the
right strategy. If humankind is still here in 2050 and still
capable of doing SETI searches, it will mean that our technology
has not yet been our own undoing -- a hopeful sign for life
generally. By then we may begin considering the active
transmission of a signal for someone else to find, at which point
we will have to tackle the difficult questions of who will speak
for Earth and what they will say."
Scientific American 1999 December
ScienceWeek http://scienceweek.com
--
Best,
Frederick Martin McNeill
Poway, California, United States of America
mmcn...@fuzzysys.com
http://www.fuzzysys.com
http://members.cox.net/fmmcneill/
*************************
Phrase of the week :
Science is a community with an attitude: people who rejoice when
a new truth defeats their past confusions, people who would
rather know reality than superstitions, people who believe that
with their minds and hearts and hands they can shape their own
destiny. Since the beginning of human time, this attitude has
threatened those whose life and fortune are based on illusion.
-- Anonymous
:-))))Snort!)
*************************
Edgar Svendsen
intelligence has more to do with our current level of technology then with
any estimate of what advanced aliens might actually do. We listen with the
tools we have, primitive as they are.
Modulating a beam of neutrinos would probably be much better then
electromagnetic radiation because the attenuation would be much less. We
could not detect such a beam (or make one) but it ought to be within the
capability of an alien civilization only a millenium or two more advanced.
Gravitons ought to be similarly effective.
We are very new to technology, in time we will be able to make a more
reasoned judgement of optimum communication techniques.
Ed
"Sir Frederick" <mmcn...@fuzzysys.com> wrote in message
news:415F5EF8...@fuzzysys.com...
Keynes
Long ago...
Some indians of the cheasepeake were convinced that
there were other indians east of the shining waters. Those
other indians of the east might possibly have better ways
of tracking the moose, or more sophisticated designs of
war bonnets, or maybe even giant canoes that didn't need
paddles. So they set up a secret society that looked to
the east for smoke signals, while sending up signal smokes
of their own. But after a few generations they gave up on
finding intelligent life beyond the east atlantic coast.
Immortalist
"Keynes" <Key...@earthlinkspam.net> wrote in message
news:i5uul0hfiejgo63r4...@4ax.com...
...and then the wind blew some ships, packed full of beings, over the horizon
from another continent
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