In 1543 Nicolaus Copernicus published De revolutionibus orbium coelestium, in which he revived the ancient Greek speculation that Earth did not sit motionless at the center of creation but, instead, orbited the Sun. Our cosmic self-esteem has been in decline ever since. Within decades of the publication of Copernicus’s book, it was almost commonplace, although dangerous, to speculate that the Sun was an ordinary star and that planetary systems orbited other stars too.
Four hundred years later, in the mid-20th century, we demoted our planet even further as we came to realize that our galaxy of a quarter-trillion stars or more was merely one "island universe" among billions. And now, thanks to NASA’s Kepler telescope, 2014 will go down in history as the year we finally knew for sure that most stars harbor planetary systems of their own.
Our little world has become lost in an immense universe that holds more planets than there are grains in a cubic mile of fine sand. To add insult to injury, the announcement in March by the Bicep2 research group that gravitational waves were generated in the very early universe supports cosmological models in which even the most distant visible galaxies are relatively near neighbors in a possibly infinite universe—a universe that is, itself, just one component of an unimaginably vast multiverse. While half a millennium ago we thought ourselves the center of the cosmos, in the modern conception of the universe we have become less significant than microbes on a mote of dust.
This is a jaw-dropping vision of an uncaring cosmos in which human beings and their passions are of no significance whatsoever. Bleak, huh?
No, actually—at least, not for me. In my view, our insignificance is significant. Our 471-year intellectual journey into cosmic oblivion raises the possibility of a scientifically justified return to a more geocentric view.
As now conceived, the cosmos is so huge that even the most unlikely things must happen occasionally, and it’s possible that a planet that, like ours, is inhabited by intelligent life is one of the oddities an immense universe occasionally generates by chance.
Imagine a comparably peculiar but less familiar planet: say, an 18-karat gold world encircled by a Saturnian ring of pure-diamond dust. That is a preposterous planet, but it’s not physically impossible, and so its existence is virtually inevitable somewhere in a universe, or multiverse, as big as ours.
Now imagine a world where chemical systems have developed the ability to copy themselves, where colonies of billions of such systems move together, as one, in search of food, and where some of those colonies stare at the stars in wonder. That’s Earth, and it may be an even more absurd and unlikely world than a planet-size engagement ring. It might therefore be one of the most interesting places in the cosmos.
I am not questioning the ability of Darwinian mechanisms to take life from simple beginnings through to the extraordinarily complex forms found on Earth four billion years later. But I am questioning whether life’s origin is an easy trick for a planet to pull off and whether the trajectory from single cells to sentience is typical even if life starts. My own research into Earth’s history suggests that one of the most important, and unlikely, components of our world’s success has been the four billion years of good weather we have enjoyed. Solar luminosity has grown 40 percent in that time, and Earth’s atmospheric composition has transformed beyond recognition. Those changes should have altered our planet’s temperature by hundreds of degrees centigrade and rendered it uninhabitable, but that simply didn’t happen.
Instead, the gradually increasing heat from our Sun has been consistently countered by decreasing greenhouse-gas concentrations, and Earth has cooled slightly through time instead of warming up. Those falling temperatures are quite mysterious since natural climate-control mechanisms might have reduced the effects of solar warming but cannot have reversed them to produce a cooling. Earth’s relatively stable climatic history can therefore be the result only of chance.
To me, that is the most convincing evidence available that good fortune played a leading role in the success of life here. Think about it: a spot in the universe where life got started, where environmental conditions were continuously life-friendly, and where evolution happened to follow the path to self-awareness. In a universe of innumerable possibilities, how often will that particular route be followed?
Planets as biodiverse as Earth will therefore be rare in the universe, but they almost certainly crop up occasionally because it is statistically implausible that there is exactly one such planet. In fact, given the enormous numbers of worlds involved, it is all but inevitable that a few biologically rich planets will also have gone on to produce sentient beings with technological civilizations. But the nearest of those will be so far away that we’ll never make contact and never detect signs of its existence.
We are, then, effectively alone in the cosmos. I don’t find that a depressing thought, however. For me, it merely emphasizes how lucky we are to be alive, how wonderful Earth is, and how important it is that we learn to look after it. But are we ready to face a universe as empty as the one I have described?
The idea that our galactic backyard is awash in intelligent life is firmly ingrained in our culture. From books to cinema, we are bombarded by visions of superluminal spaceships fighting for dominance in a galaxy entirely inhabited by six-foot-tall bipeds who speak better English than I do. Even within science there are erudite texts explaining that, because of convergent evolution, those stately, sentient bipeds with 20/20 color vision are a likely product of evolution on any inhabited world. But even if those arguments are correct, convergent evolution is irrelevant if biospheres as complex and beautiful as Earth’s are a cosmic oddity.
That hasn’t stopped mainstream scientists from embracing the Search for Extra Terrestrial Intelligence, which has been looking for artificial radio transmissions from space ever since early radio pioneers tried to detect signals from Mars more than a century ago. SETI has since become a rigorous, sophisticated, and systematic attempt to search the electromagnetic spectrum for signals from advanced civilizations elsewhere in our galaxy. But, so far, all such searches have failed.
In contrast, astronomers have engaged in a spectacularly successful search for exoplanets—planets around other stars. The first such worlds were discovered with Earth-based optical telescopes and radio telescopes in the 1990s. Since then, we have found almost 2,000 more. NASA’s Kepler mission, a particularly prolific discoverer of alien worlds, has found 961 planets, with more expected over the next few years. Given those numbers we can truly start to judge what’s typical and what’s not, and it’s worth noting that no true Earth analogues have yet been found.
Despite all this scientific and cultural enthusiasm for alien life, it remains possible, indeed probable, that our search for other inhabited worlds will fail. What will happen if, after 20, 50, or 100 years of looking, we have still found nothing? Will enthusiasm wane? Will our civilization become more inward looking and insular, or will this failure focus our minds on things that really matter, such as looking after our own world? History can help with such questions. We have been in similar situations before.
Consider the Great Disappointment of 1844, when a widely anticipated second coming of Christ didn’t materialize. The prophet of his return, William Miller, was undoubtedly sincere in a belief based upon intense study of the Bible, and, after more than a decade of preaching, he built up a following that some have estimated at 100,000 people or more. But when the initial date of rapture, March 21, came and went, disillusion set in. More important, his followers were subjected to astonishing vilification by society at large. Millerite churches were burned, mobs attacked congregations, and the newspapers of the day poured scorn on them.
More recently the Seekers who followed Dorothy Martin experienced similar treatment and responded in similar ways. Martin was a housewife from Chicago who predicted that Earth would be destroyed in a great flood on December 21, 1951. Her followers were to be saved by flying saucers that would turn up the night before. When the flying saucers failed to arrive, the Seekers were told that their faith had saved our planet from destruction, but, despite that singular service to the world, the group was still met with derision from the press in the days that followed. Martin went on to found other UFO cults and eventually died in 1992 as a leading member of a New Age group in Arizona.
The events of December 20 and 21, 1951, played a central role in the development of the theory of cognitive dissonance—loosely speaking, the theory of how we convince ourselves that we’re right even when evidence says otherwise. The group had been infiltrated by the psychologist Leon Festinger, and he documented the events of that evening in his classic 1956 book When Prophecy Fails. Cognitive dissonance may well come to the fore if a successful search for off-world life still eludes us in several decades.
The "discovery" of cold fusion, in 1989, astonished the world since it suggested that an almost inexhaustible supply of energy could be obtained from relatively simple and cheap equipment. To recreate controlled nuclear fusion, the process that powers the stars, we didn’t need to spend billions of dollars on a complex apparatus designed to magnetically suspend multimillion-degree plasmas away from physical walls that would otherwise be instantly vaporized. Instead, we just needed a jar of heavy water and some palladium electrodes.
The initial reports gave rise to immense excitement both inside and outside the scientific world, but, when scientists failed to reproduce the findings, there was understandable disappointment. Supporters of cold fusion stuck by their results nonetheless and explained away negative results as experimental incompetence by their detractors, who, in turn, became increasingly vociferous in their criticism of the original experiments. Today this is a toxic area for research. Any scientist attempting to publish a cold-fusion paper would be committing career suicide.
Whatever the rights and wrongs of the Millerites, the Seekers, and the cold-fusion advocates, the pattern that emerges whenever high expectations are disappointed is of a tight inner circle that sticks to its views while increasingly vitriolic abuse pours in from outsiders. In the context of the search for alien life, this pattern worries me. If I’m right that extraterrestrial life will prove elusive, the future of astrobiology could be one of vilification and cultification. Will it then shrink to an arcane field studied by increasingly isolated misfits who endure the taunts of colleagues and the wider public? Will it be reduced to analysis and reanalysis of the same data over and over again because no one will finance new investigations? Even worse, a failure to find life elsewhere could rebound on the whole of science if its practitioners are perceived as more interested in the 21st-century equivalent of counting angels on the head of a pin than they are in solving the very real problems faced by humanity.
My view, then, is that we’re unlikely to succeed in finding life outside the solar system, and this failure could eventually lead to cynicism toward science and scientists. Am I advocating that we cease astrobiological and exoplanetary studies? Absolutely not. My analysis of life’s improbability could be flawed, and perhaps alien life will be found soon. Furthermore, exoplanets are, of course, fascinating in their own right, even if they’re devoid of life. Curiosity is one of mankind’s more endearing characteristics, and the search for life speaks to the poetry of the human soul. Surely culture, love, and curiosity are what make life worth living.
The solution, then, is not to restrict NASA to the prosaic business of exploring the near solar system for minerals and dropping all support for curiosity-driven space science. Science should not turn inward and become restricted entirely to practical matters with direct application to our all-too-real problems of poverty, global warming, and overpopulation.
Astrobiologists, however, need to manage expectations more sensibly and avoid giving the impression that major discoveries are inevitable and just around the corner. We should emphasize that the search for life beyond Earth is a high-risk, high-reward venture. The chances of short-term success are minute, but it’s hard to imagine any discovery that would have more impact on the understanding of our place in the universe. We must keep looking. But let’s search with realistic expectations and with the realization that the search itself is an expression of strangely amazing and amazed life on our own astonishingly unlikely planet.
David Waltham is an astrobiologist and geophysicist in the department of earth sciences at Royal Holloway College at the University of London. He is the author of Lucky Planet: Why Earth Is Exceptional—and What That Means for Life in the Universe, new from Basic Books.