Darling, David J. Life Everywhere: The Maverick Science of Astrobiology. New York: Basic Books, 2001. ISBN 0-465-01563-8.

October 2001 Permalink

Davies, Paul. The Eerie Silence. New York: Houghton Mifflin Harcourt, 2010. ISBN 978-0-547-13324-9.
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.

December 2010 Permalink

Ekers, Ronald D. et al., eds. SETI 2020. Mountain View, CA: SETI Institute, 2002. ISBN 0-9666335-3-9.

March 2003 Permalink

McConnell, Brian. Beyond Contact: A Guide to SETI and Communicating with Alien Civilizations. Sebastopol, CA: O'Reilly, 2001. ISBN 0-596-00037-5.

April 2002 Permalink

Scoles, Sarah. Making Contact. New York: Pegasus Books, 2017. ISBN 978-1-68177-441-1.
There are few questions in our scientific inquiry into the universe and our place within it more profound than “are we alone?” As we have learned more about our world and the larger universe in which it exists, this question has become ever more fascinating. We now know that our planet, once thought the centre of the universe, is but one of what may be hundreds of billions of planets in our own galaxy, which is one of hundreds of billions of galaxies in the observable universe. Not long ago, we knew only of the planets in our own solar system, and some astronomers believed planetary systems were rare, perhaps formed by freak encounters between two stars following their orbits around the galaxy. But now, thanks to exoplanet hunters and, especially, the Kepler spacecraft, we know that it's “planets, planets, everywhere”—most stars have planets, and many stars have planets where conditions may be suitable for the origin of life.

If this be the case, then when we gaze upward at the myriad stars in the heavens, might there be other eyes (or whatever sense organs they use for the optical spectrum) looking back from planets of those stars toward our Sun, wondering if they are alone? Many are the children, and adults, who have asked themselves that question when standing under a pristine sky. For the ten year old Jill Tarter, it set her on a path toward a career which has been almost coterminous with humanity's efforts to discover communications from extraterrestrial civilisations—an effort which continues today, benefitting from advances in technology unimagined when she undertook the quest.

World War II had seen tremendous advancements in radio communications, in particular the short wavelengths (“microwaves”) used by radar to detect enemy aircraft and submarines. After the war, this technology provided the foundation for the new field of radio astronomy, which expanded astronomers' window on the universe from the traditional optical spectrum into wavelengths that revealed phenomena never before observed nor, indeed, imagined, and hinted at a universe which was much larger, complicated, and violent than previously envisioned.

In 1959, Philip Morrison and Guiseppe Cocconi published a paper in Nature in which they calculated that using only technologies and instruments already existing on the Earth, intelligent extraterrestrials could send radio messages across the distances to the nearby stars, and that these messages could be received, detected, and decoded by terrestrial observers. This was the origin of SETI—the Search for Extraterrestrial Intelligence. In 1960, Frank Drake used a radio telescope to search for signals from two nearby star systems; he heard nothing.

As they say, absence of evidence is not evidence of absence, and this is acutely the case in SETI. First of all, consider that you must first decide what kind of signal aliens might send. If it's something which can't be distinguished from natural sources, there's little hope you'll be able to tease it out of the cacophony which is the radio spectrum. So we must assume they're sending something that doesn't appear natural. But what is the variety of natural sources? There's a dozen or so Ph.D. projects just answering that question, including some surprising discoveries of natural sources nobody imagined, such as pulsars, which were sufficiently strange that when first observed they were called “LGM” sources for “Little Green Men”. On what frequency are they sending (in other words, where do we have to turn our dial to receive them, for those geezers who remember radios with dials)? The most efficient signals will be those with a very narrow frequency range, and there are billions of possible frequencies the aliens might choose. We could be pointed in the right place, at the right time, and simply be tuned to the wrong station.

Then there's that question of “the right time”. It would be absurdly costly to broadcast a beacon signal in all directions at all times: that would require energy comparable to that emitted by a star (which, if you think about it, does precisely that). So it's likely that any civilisation with energy resources comparable to our own would transmit in a narrow beam to specific targets, switching among them over time. If we didn't happen to be listening when they were sending, we'd never know they were calling.

If you put all of these constraints together, you come up with what's called an “observational phase space”—a multidimensional space of frequency, intensity, duration of transmission, angular extent of transmission, bandwidth, and other parameters which determine whether you'll detect the signal. And that assumes you're listening at all, which depends upon people coming up with the money to fund the effort and pursue it over the years.

It's beyond daunting. The space to be searched is so large, and our ability to search it so limited, that negative results, even after decades of observation, are equivalent to walking down to the seashore, sampling a glass of ocean water, and concluding that based on the absence of fish, the ocean contained no higher life forms. But suppose you find a fish? That would change everything.

Jill Tarter began her career in the mainstream of astronomy. Her Ph.D. research at the University of California, Berkeley was on brown dwarfs (bodies more massive than gas giant planets but too small to sustain the nuclear fusion reactions which cause stars to shine—a brown dwarf emits weakly in the infrared as it slowly radiates away the heat from the gravitational contraction which formed it). Her work was supported by a federal grant, which made her uncomfortable—what relevance did brown dwarfs have to those compelled to pay taxes to fund investigating them? During her Ph.D. work, she was asked by a professor in the department to help with an aged computer she'd used in an earlier project. To acquaint her with the project, the professor asked her to read the Project Cyclops report. It was a conversion experience.

Project Cyclops was a NASA study conducted in 1971 on how to perform a definitive search for radio communications from intelligent extraterrestrials. Its report [18.2 Mb PDF], issued in 1972, remains the “bible” for radio SETI, although advances in technology, particularly in computing, have rendered some of its recommendations obsolete. The product of a NASA which was still conducting missions to the Moon, it was grandiose in scale, envisioning a large array of radio telescope dishes able to search for signals from stars up to 1000 light years in distance (note that this is still a tiny fraction of the stars in the galaxy, which is around 150,000 light years in diameter). The estimated budget for the project was between 6 and 10 billion dollars (multiply those numbers by around six to get present-day funny money) spent over a period of ten to fifteen years. The report cautioned that there was no guarantee of success during that period, and that the project should be viewed as a long-term endeavour with ongoing funding to operate the system and continue the search.

The Cyclops report arrived at a time when NASA was downsizing and scaling back its ambitions: the final three planned lunar landing missions had been cancelled in 1970, and production of additional Saturn V launch vehicles had been terminated the previous year. The budget climate wasn't hospitable to Apollo-scale projects of any description, especially those which wouldn't support lots of civil service and contractor jobs in the districts and states of NASA's patrons in congress. Unsurprisingly, Project Cyclops simply landed on the pile of ambitious NASA studies that went nowhere. But to some who read it, it was an inspiration. Tarter thought, “This is the first time in history when we don't just have to believe or not believe. Instead of just asking the priests and philosophers, we can try to find an answer. This is an old and important question, and I have the opportunity to change how we try to answer it.” While some might consider searching the sky for “little green men” frivolous and/or absurd, to Tarter this, not the arcana of brown dwarfs, was something worthy of support, and of her time and intellectual effort, “something that could impact people's lives profoundly in a short period of time.”

The project to which Tarter had been asked to contribute, Project SERENDIP (a painful acronym of Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations) was extremely modest compared to Cyclops. It had no dedicated radio telescopes at all, nor even dedicated time on existing observatories. Instead, it would “piggyback” on observations made for other purposes, listening to the feed from the telescope with an instrument designed to detect the kind of narrow-band beacons envisioned by Cyclops. To cope with the problem of not knowing the frequency on which to listen, the receiver would monitor 100 channels simultaneously. Tarter's job was programming the PDP 8/S computer to monitor the receiver's output and search for candidate signals. (Project SERENDIP is still in operation today, employing hardware able to simultaneously monitor 128 million channels.)

From this humble start, Tarter's career direction was set. All of her subsequent work was in SETI. It would be a roller-coaster ride all the way. In 1975, NASA had started a modest study to research (but not build) technologies for microwave SETI searches. In 1978, the program came into the sights of senator William Proxmire, who bestowed upon it his “Golden Fleece” award. The program initially survived his ridicule, but in 1982, the budget zeroed out the project. Carl Sagan personally intervened with Proxmire, and in 1983 the funding was reinstated, continuing work on a more capable spectral analyser which could be used with existing radio telescopes.

Buffeted by the start-stop support from NASA and encouraged by Hewlett-Packard executive Bernard Oliver, a supporter of SETI from its inception, Tarter decided that SETI needed its own institutional home, one dedicated to the mission and able to seek its own funding independent of the whims of congressmen and bureaucrats. In 1984, the SETI Institute was incorporated in California. Initially funded by Oliver, over the years major contributions have been made by technology moguls including William Hewlett, David Packard, Paul Allen, Gordon Moore, and Nathan Myhrvold. The SETI Institute receives no government funding whatsoever, although some researchers in its employ, mostly those working on astrobiology, exoplanets, and other topics not directly related to SETI, are supported by research grants from NASA and the National Science Foundation. Fund raising was a skill which did not come naturally to Tarter, but it was mission critical, and so she mastered the art. Today, the SETI Institute is considered one of the most savvy privately-funded research institutions, both in seeking large donations and in grass-roots fundraising.

By the early 1990s, it appeared the pendulum had swung once again, and NASA was back in the SETI game. In 1992, a program was funded to conduct a two-pronged effort: a targeted search of 800 nearby stars, and an all-sky survey looking for stronger beacons. Both would employ what were then state-of-the-art spectrum analysers able to monitor 15 million channels simultaneously. After just a year of observations, congress once again pulled the plug. The SETI Institute would have to go it alone.

Tarter launched Project Phoenix, to continue the NASA targeted search program using the orphaned NASA spectrometer hardware and whatever telescope time could be purchased from donations to the SETI Institute. In 1995, observations resumed at the Parkes radio telescope in Australia, and subsequently a telescope at the National Radio Astronomy Observatory in Green Bank, West Virginia, and the 300 metre dish at Arecibo Observatory in Puerto Rico. The project continued through 2004.

What should SETI look like in the 21st century? Much had changed since the early days in the 1960s and 1970s. Digital electronics and computers had increased in power a billionfold, not only making it possible to scan a billion channels simultaneously and automatically search for candidate signals, but to combine the signals from a large number of independent, inexpensive antennas (essentially, glorified satellite television dishes), synthesising the aperture of a huge, budget-busting radio telescope. With progress in electronics expected to continue in the coming decades, any capital investment in antenna hardware would yield an exponentially growing science harvest as the ability to analyse its output grew over time. But to take advantage of this technological revolution, SETI could no longer rely on piggyback observations, purchased telescope time, or allocations at the whim of research institutions: “SETI needs its own telescope”—one optimised for the mission and designed to benefit from advances in electronics over its lifetime.

In a series of meetings from 1998 to 2000, the specifications of such an instrument were drawn up: 350 small antennas, each 6 metres in diameter, independently steerable (and thus able to be used all together, or in segments to simultaneously observe different targets), with electronics to combine the signals, providing an effective aperture of 900 metres with all dishes operating. With initial funding from Microsoft co-founder Paul Allen (and with his name on the project, the Allen Telescope Array), the project began construction in 2004. In 2007, observations began with the first 42 dishes. By that time, Paul Allen had lost interest in the project, and construction of additional dishes was placed on hold until a new benefactor could be found. In 2011, a funding crisis caused the facility to be placed in hibernation, and the observatory was sold to SRI International for US$ 1. Following a crowdfunding effort led by the SETI Institute, the observatory was re-opened later that year, and continues operations to this date. No additional dishes have been installed: current work concentrates on upgrading the electronics of the existing antennas to increase sensitivity.

Jill Tarter retired as co-director of the SETI Institute in 2012, but remains active in its scientific, fundraising, and outreach programs. There has never been more work in SETI underway than at the present. In addition to observations with the Allen Telescope Array, the Breakthrough Listen project, funded at US$ 100 million over ten years by Russian billionaire Yuri Milner, is using thousands of hours of time on large radio telescopes, with a goal of observing a million nearby stars and the centres of a hundred galaxies. All data are available to the public for analysis. A new frontier, unimagined in the early days of SETI, is optical SETI. A pulsed laser, focused through a telescope of modest aperture, is able to easily outshine the Sun in a detector sensitive to its wavelength and pulse duration. In the optical spectrum, there's no need for fancy electronics to monitor a wide variety of wavelengths: all you need is a prism or diffraction grating. The SETI Institute has just successfully completed a US$ 100,000 Indiegogo campaign to crowdfund the first phase of the Laser SETI project, which has as its ultimate goal an all-sky, all-the-time search for short pulses of light which may be signals from extraterrestrials or new natural phenomena to which no existing astronomical instrument is sensitive.

People often ask Jill Tarter what it's like to spend your entire career looking for something and not finding it. But she, and everybody involved in SETI, always knew the search would not be easy, nor likely to succeed in the short term. The reward for engaging in it is being involved in founding a new field of scientific inquiry and inventing and building the tools which allow exploring this new domain. The search is vast, and to date we have barely scratched the surface. About all we can rule out, after more than half a century, is a Star Trek-like universe where almost every star system is populated by aliens chattering away on the radio. Today, the SETI enterprise, entirely privately funded and minuscule by the standards of “big science”, is strongly coupled to the exponential growth in computing power and hence, roughly doubles its ability to search around every two years.

The question “are we alone?” is one which has profound implications either way it is answered. If we discover one or more advanced technological civilisations (and they will almost certainly be more advanced than we—we've only had radio for a little more than a century, and there are stars and planets in the galaxy billions of years older than ours), it will mean it's possible to grow out of the daunting problems we face in the adolescence of our species and look forward to an exciting and potentially unbounded future. If, after exhaustive searches (which will take at least another fifty years of continued progress in expanding the search space), it looks like we're alone, then intelligent life is so rare that we may be its only exemplar in the galaxy and, perhaps, the universe. Then, it's up to us. Our destiny, and duty, is to ensure that this spark, lit within us, will never be extinguished.

September 2017 Permalink

Shostak, Seth. Confessions of an Alien Hunter. Washington: National Geographic, 2009. ISBN 978-1-4262-0392-3.
This book was published in 2009, the fiftieth anniversary of the modern search for extraterrestrial intelligence (SETI), launched by Cocconi and Morrison's Nature paper which demonstrated that a narrowband microwave beacon transmitted by intelligent extraterrestrials would be detectable by existing and anticipated radio telescopes on Earth. In recent years, the SETI Institute has been a leader in the search for alien signals and the author, as Senior Astronomer at the Institute, a key figure in its ongoing research.

On the night of June 24th, 1997 the author, along with other researchers, were entranced by the display on their computer monitors of a signal relayed from a radio telescope in West Virginia aimed at an obscure dwarf star named YZ Ceti 12 light years from the Sun. As a faint star prone to flares, it seemed an improbable place to find an alien civilisation, but was being monitored as part of a survey of all stars within 15 light years of the Sun, regardless of type. “Candidate signals” are common in SETI: most are due to terrestrial interference, transmissions from satellites or passing aircraft, or transient problems with the instrumentation processing the signal. These can usually be quickly excluded by simple tests such as aiming the antenna away from the source, testing whether the source is moving with respect to the Earth at a rate different than that of the distant stars, or discovering that a second radio telescope in a different location is unable to confirm the signal. Due to a mechanical failure at the backup telescope, the latter test was not immediately available, but all of the other tests seemed to indicate that this was the real deal, and those observing the signal had to make the difficult decision whether to ask other observatories to suspend their regular research and independently observe the source, and/or how to announce the potential discovery to the world. All of these difficult questions were resolved when it was discovered that a small displacement of the antenna from the source, which should have caused a Gaussian fall-off in intensity, in fact changed the signal amplitude not at all. Whatever the source may have been, it could not be originating at YZ Ceti. Shortly thereafter, the signal was identified as a “side lobe” reception of the SOHO spacecraft at the Sun-Earth L1 point. Around this time, the author got a call from a reporter from the New York Times who had already heard rumours of the detection and was trawling for a scoop. So much for secrecy and rumours of cover-ups in the world of SETI! By the evidence, SETI leaks like a sieve.

This book provides an insider's view of the small but fascinating world of SETI: a collective effort which has produced nothing but negative results over half a century, yet holds the potential, with the detection of a single confirmed alien transmission, of upending our species' view of its place in the cosmos and providing hope for the long-term survival of intelligent civilisations in the universe. There is relatively little discussion of the history of SETI, which makes sense since the ongoing enterprise directly benefits from the exponential growth in the capabilities of electronics and computation, and consequentially the breadth and sensitivity of results in the last few years will continue to dwarf those of all earlier searches. Present-day searches, both in the microwave spectrum and looking for ultra-short optical pulses, are described in detail, along with the prospects for the near future, in which the Allen Telescope Array will vastly expand the capability of SETI.

The author discusses the puzzles posed by the expectation that (unless we're missing something fundamental), the window between a technological civilisation's developing the capability to perform SETI research as we presently do it and undergoing a technological singularity which will increase its intelligence and capabilities to levels humans cannot hope to comprehend may be on the order of one to two centuries. If this is the case, any extraterrestrials we contact are almost certain to be these transcendent machine intelligences, whose motivations in trying to contact beings in an ephemeral biological phase such as our own are difficult to imagine. But if such beings are common, shouldn't their cosmological masterworks be writ for all to see in the sky? Well, maybe they are! Vive l'art cosmologique!

What would be the impact of a confirmed detection of an alien transmission? The author suggests, and I tend to concur, probably a lot less than breathless authors of fiction might expect. After all, in the late 19th and early 20th century, Percival Lowell's case for an intelligent canal-building civilisation on Mars was widely accepted, and it did not cause any huge disruption to human self-perception. When I was in high school, many astronomy texts said it was likely Mars was home to lichen-like organisms which accounted for the seasonal changes observed on the planet. And as late as the landing of Viking I on Mars, which this scrivener observed from the Jet Propulsion Laboratory auditorium on July 20th, 1976, the President of the United States asked from the White House whether the lander's camera would be able to photograph any Martian animals rambling around the landscape. (Yes, it would. No, it didn't—although the results of the microbial life detection experiments are still disputed.)

This book, a view from inside the contemporary SETI enterprise, is an excellent retrospective on modern SETI and look at its future prospects at the half century mark. It is an excellent complement to Paul Davies's The Eerie Silence (December 2010), which takes a broader approach to the topic, looking more deeply into the history of the field and exploring how, from the present perspective, the definition of alien intelligence and the ways in which we might detect it should be rethought based on what we've learnt in the last five decades. If I had to read only one book on the topic, I would choose the Davies book, but I don't regret reading them both.

The Kindle edition is reasonably well produced, although there are some formatting oddities, and for some reason the capital “I”s in chapter titles have dots above them. There is a completely useless “index” in which items are not linked to their references in the text.

March 2011 Permalink

Trefil, James. Are We Unique?. New York: John Wiley & Sons, 1997. ISBN 0-471-24946-7.

December 2002 Permalink

Webb, Stephen. If the Universe Is Teeming with Aliens…Where Is Everybody?. New York: Copernicus, 2002. ISBN 0-387-95501-1.

October 2003 Permalink