- Davies, Paul. The Eerie Silence. New York: Houghton Mifflin Harcourt, 2010. ISBN 978-0-547-13324-9.
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The year 2009 marked the fiftieth anniversary of the
Nature paper
by Cocconi and Morrison which marked the beginning of the modern
era in the search for extraterrestrial intelligence (SETI). They
argued that the optimal channel by which technological civilisations
in other star systems who wished to establish contact with
those nearby in the galaxy would be narrowband microwave transmissions,
perhaps pulse modulated in a pattern that would distinguish them from
natural sources. Further, they demonstrated that radio telescopes existing
at the time (which were modest compared to those already planned for
construction in the near future) would suffice to send and receive such
a signal over distances of tens of light years. The following year,
Frank Drake used a 26 metre dish at the National Radio Astronomy Observatory
to search for such signals from two nearby sun-like stars in
Project Ozma.
Over the succeeding half-century, SETI has been an off and on affair, with
a variety of projects with different search strategies. Since the 1990s
a low level of SETI activity has been maintained, both using radio telescopes
to conduct targeted searches and piggybacking on other radio astronomy
observations to conduct a sky survey for candidate signals. There is still
a substantial “giggle factor” associated with “listening for
ET”, and funding and allocation of telescope time for SETI is minuscule
compared to other radio astronomy research. SETI has been a direct beneficiary
of the exponential growth in computing power available for a given cost, and
now employs spectrum analysers able to monitor millions or billions of
narrowband channels simultaneously, largely eliminating the original conundrum
of SETI: guessing the frequency on which the aliens would be transmitting.
The Allen Telescope Array,
now under construction, will increase the capability of SETI observations by
orders of magnitude, and will continue to benefit from progress in
microelectronics and computing.
The one thing that all SETI projects to date have in common is that
they haven't found anything. Indeed, the SETI enterprise, taken as a
whole, may be the longest-pursued unsuccessful search for a phenomenon
in the entire history of science. The reason people don't abandon the
enterprise in disappointment is that detection of a signal from
an intelligent extraterrestrial source would have profound consequences
for understanding the human species' place in the cosmos, the prospects
for long-term survival of technological civilisations, and potential
breakthroughs in all fields of knowledge if an advanced species shares
their knowledge with beginners barely evolved from apes. Another reason
the searchers persist is the knowledge that they've barely scratched
the surface of the “search space”, having only examined a
minuscule fraction of potential targets in the galaxy, and a limited
range of potential frequencies and forms of modulation a communicating
civilisation might employ to contact others in the galaxy. Finally,
continued advances in electronics and computing are making it possible
to broaden the scope of the search at a rapidly increasing rate with
modest budgets.
Still, after fifty years of searching (intermittently) and finding nothing,
it's worth taking a step back and thinking about what that result
might mean. In this book, the author revisits the history of SETI
programs to date, the assumptions and logic upon which the targets
they seek were based, and argues that while conventional microwave
searches for narrowband beacons should continue, it is time for a
“new SETI”, based on the original mission—search
for extraterrestrial intelligence, not just a search for
narrowband microwave signals. “Old SETI” was very much
based on assumptions about the properties of potential communicating
civilisations grounded in the technologies of the 1950s. A great deal
has happened since then technologically (for example, the Earth, as
seen from deep space, has increasingly grown “radio dark”
as high-power broadcast transmitters have been supplanted by
optical fibres, cable television systems, and geosynchronous
communication satellites which radiate little energy away from
the Earth).
In 1959, the pioneers contemplating a SETI program based on the tools of radio astronomy mostly assumed that the civilisations whose beacons they hoped to discover would be biological organisms much like humans or their descendants, but endowed with the scientific and technological capabilities of a much longer period of time. (For statistical reasons, it is vanishingly improbable that humans would make contact with another intelligent species at a comparable state of development, since humans have had the capability to make contact for less than a century, and if other civilisations are comparably short-lived there will never be more than one in the galaxy at any given time. Hence, any signal we receive will necessarily be from a sender whose own technological civilisation is much older than our own and presumably more advanced and capable.) But it now appears probable that unless human civilisation collapses, stagnates, or is destroyed by barbarism (I put the collective probability of these outcomes at around fifty-fifty), or that some presently unenvisioned constraint puts a lid on the exponential growth of computing and communication capability, that before long, probably within this century, our species will pass through a technological singularity which will witness the emergence of artificial intelligence with intellectual capabilities on the order of 1010 to 1015 times that of present-day humans. Biological humans may continue to exist (after all, the evolution of humans didn't impact the dominance of the biosphere by bacteria), but they will no longer determine the course of technological evolution on this planet and beyond. Asking a present-day human to comprehend the priorities and capabilities of one of these successor beings is like asking a butterfly to understand Beethoven's motivations in writing the Ninth Symphony.
And yet, unless we're missing something terribly important, any aliens we're likely to contact are overwhelmingly probable to be such forbidding machine intelligences, not Romulans, Klingons, Ferengi, or even the Borg. Why would such super beings try to get our attention by establishing interstellar beacons? What would they have to say if they did contact us? Consider: how much effort does our own species exert in making contact with or carrying on a dialogue with yeast? This is the kind of gap which will exist between humans and the products of millions of years of teleological development. And so, the author argues, while keeping a lookout for those elusive beacons (and also ultra-short laser pulses, which are an alternative mechanism of interstellar signalling unimagined when “old SETI” was born), we should also cast the net much wider, looking for the consequences of an intelligence whose motivations and capabilities we cannot hope to envision. Perhaps they have seeded the galaxy with self-reproducing von Neumann probes, one of which is patiently orbiting in the asteroid belt or at one of the Earth-Sun Lagrangian points waiting to receive a ping from us. (And speaking of that, what about those long delayed echoes anyway?) Maybe their wave of exploration passed by the solar system more than three billion years ago and seeded the Earth with the ancestral cell from which all terrestrial life is descended. Or maybe they left a different kind of life, perhaps in their garbage dumps, which lives on as a “shadow biosphere” to this day, undetected because our surveys for life don't look for biochemistry which is different from that of our own. Heck, maybe they even left a message! We should also be on the lookout for things which don't belong, like discrepancies in isotope abundances which may be evidence of alien technology in distant geological time, or things which are missing. Where did all of those magnetic monopoles which should have been created in the Big Bang go, anyway? Or maybe they've moved on to some other, richer domain in the universe. According to the consensus model of cosmology, we have no idea whatsoever what more than 95% of the universe is made of. Maybe they've transcended their juvenile baryonic origins and decamped to the greener fields we call, in our ignorance, “dark matter” and “dark energy”. While we're pointing antennas at obsolete stars in the sky, maybe they're already here (and everywhere else), not as UFOs or alien invaders, but super-intelligences made of structures which interact only gravitationally with the thin scum of baryonic matter on top of the rich ocean of the universe. Maybe their galactic Internet traffic is already tickling the mirrors of our gravitational wave detectors at intensities we can't hope to detect with our crude technologies. Anybody who's interested in these kinds of deep questions about some of the most profound puzzles about our place in the universe will find this book a pure delight. The Kindle edition is superbly produced, with high-resolution colour plates which display beautifully on the iPad Kindle reader, and that rarest and most welcome of attributes in an electronic book, an index which is properly linked to the text. The Kindle edition is, however, more expensive than the hardcover as of this writing.
