Where Is Everybody?
THE EERIE SILENCE: Renewing Our Search for Alien Intelligence. Paul Davies. xvi + 240 pp. Houghton Mifflin Harcourt, 2010. $27.
On August 15, 1977, at 11:16 p.m. Eastern Daylight Time, the Big Ear radio telescope in Delaware, Ohio, received a powerful transmission from an otherwise unremarkable region of the constellation Sagittarius. The signal, which had a frequency of 1420 megahertz and lasted 72 seconds, was of record-breaking intensity. It wasn’t noticed initially, but several days later Jerry Ehman, an astronomer working on the Big Ear’s sky survey in his spare time, reviewed the reams of computer printouts that the telescope generated and immediately saw that an exceptionally strong signal had been picked up. Astonished, he scribbled “Wow!” in the left margin of the page.
A great deal of analysis during the ensuing years has never yielded a satisfactory explanation of who or what caused what has come to be known as Ehman’s “Wow!” signal. Meticulous reexaminations of the spot of sky from which it sprang have turned up nothing. It stands as a tiny question mark within the vast body of data obtained in the course of unsuccessful astronomical searches for extraterrestrial intelligence (SETI). On the whole, these data point overwhelmingly to our civilization’s profound cosmic isolation.
In The Eerie Silence, Paul Davies of Arizona State University’s Beyond Center takes the 50th anniversary of the first radio SETI experiments as a point of departure for exploring the meaning and implications of the failure of such efforts. Are we missing the boat in our approach to the search? Are we hopelessly naive? Or is the great silence informing us that nobody is out there? If so, what makes us so unusual? Is life itself a galactic rarity? Do civilizations invariably clobber themselves soon after they arise on the scene? Davies weaves all of these speculative threads into a book that is, for the most part, mesmerizing.
Proponents of SETI projects such as the ambitious new Allen Telescope Array might argue that absence of evidence should not yet be taken as evidence of absence, because the past efforts to detect alien signals have been trivially small in comparison with what might be required for success. According to this view, a big-picture assessment would be premature at this point; patience and perseverance are all that is needed.
Davies is certainly sympathetic to such arguments, which is not surprising given that he has long been associated with SETI and currently chairs the SETI Post-Detection Taskgroup, a diverse and rather eclectic committee trying to figure out the best ways of handling the successful detection of an artificial astronomical signal, should that ever come to pass. In a fascinating chapter of the book, he speculates about what would transpire if contact were established. I enjoyed his insider’s perspective on how the media cover those fields of science that generate intense public interest. He expects that in the age of the Internet, the blogosphere and eroding old-media control over the flow of information, the success of SETI would likely unfold in a rather dramatic and unpredictable fashion. The chapter goes on to explore what the consequences of contact would be for science, philosophy, politics and religion.
Through his position at the Beyond Center, Davies is at the nexus of the various disciplines that contribute to modern astrobiology research. So he’s well equipped to discuss developments in all these areas. In particular, he spends several chapters exploring the molecular imperatives for life. Given that we have one good example of ultrasophisticated life forms evolving from humble beginnings, finding even simple biological organisms elsewhere in the cosmos would suggest that other examples of intelligent life very likely exist. Davies does an excellent job of reporting from the front lines of molecular biology. He explores the possibilities that life on Earth may have had multiple geneses, that our planet might be host to an undiscovered “shadow biosphere” of alternative forms of microbial life, and that life on Mars may have originated independently of life on Earth. To find scientific confirmation of any of these things might constitute an immediate and paradigm-shifting breakthrough. Should we discover it to be the case that life forms easily, then the eerie silence is suddenly all the more eerie.
With SETI on the verge of its golden anniversary, many readers are by now probably familiar with the famous Drake Equation for calculating the number of extraterrestrial civilizations in the Milky Way, civilizations with which we might come into contact. That equation has engendered countless Astronomy 101–level discussions. Davies deftly handles this well-worn material by discussing it in terms of Brandon Carter and Robin Hanson’s “Great Filter.” Their basic idea is that, given that we don’t see any evidence that other intelligent creatures have taken over big chunks of the cosmos, some Great Filter must be operating to prevent life from evolving to the point of colonizing our galaxy. If one posits several steps (the emergence of eukaryotes, sexual reproduction, multicellular organisms and big brains, for example) on the evolutionary path that leads to such colonization, then one or more of those steps must be very improbable. Perhaps we’ve already made it through the Great Filter and will go on to colonize the visible universe ourselves. But it may be the case that civilizations as advanced as ours typically go on to destroy themselves before they reach the star-hopping phase, and that we have a Great Filter in our future.
Carter and Hanson assume, Davies says, that “each step [on the road to intelligence] is so improbable it would take, on its own, far longer on average than the lifetime of a typical star.” Using the equations of probability theory, they show that if there are N improbable steps in the development of intelligent life, then in the unlikely event that intelligent life does happen to emerge, the expected duration between each step is about 1/Nth of the total amount of time available. Applying this hypothesis to the situation on Earth, Davies argues that, given that the planet has just passed the 4.5-billion-year mark, and given that the biosphere likely has something on the order of 800 million years left before the Sun begins to turn into a red giant star and incinerate us, then about six improbable events, spaced something on the order of 800 million years apart, must have occurred in order for us to have arrived on the galactic stage. He concludes that, for the most part, this fits reasonably well with the fossil record.
If Carter is right about the time for intelligent life to arise being far greater than the typical lifetime of a star, then the evolution of intelligent life on Earth is a freak event, says Davies. If that’s not the case, if the steps leading to intelligent life are not so unlikely as to have happened only once, then the eerie silence may have a more ominous explanation: The Great Filter might present one final bottleneck to galactic aspirations. It may be that once a civilization gains the ability to build radios and lasers, it gains the ability to destroy itself. In Carl Sagan’s heyday, the specter of nuclear annihilation was seen as the most likely road to disaster. Several decades on, it is environmental collapse that looms as the most credible threat.
I wonder, though, whether there might be a more pedestrian explanation. As a society we’ve become conditioned to receiving ever-faster answers to our queries. Blackberries buzz in our pockets. Text messages, tweets and e-mails pile up 24/7 and subside into the unanswered strata of mental to-do lists. Could it be that members of any society technologically advanced enough to undertake interstellar communication are so distracted by an immediately accessible and dazzling array of ephemera that they have no patience for communications that would take such a vast stretch of time?
Gregory P. Laughlin is a professor of astronomy and astrophysics at the University of California, Santa Cruz, where he also teaches astrobiology in the Department of Earth and Planetary Sciences.