Origins: Fourteen Billion Years of Cosmic Evolution (25 page)

By completing our
search for life in the solar system, we might seem to have finished our tour through the fundamental questions linked to our cosmic origins. We cannot, however, leave this arena without a look at the great origin issue that lies in the future: the origin of our contact with other civilizations. No astronomical topic grips the public imagination more vividly, and none offers a better chance to draw together the strands of what we have learned about the universe. Now that we know something about how life might begin on other worlds, let’s examine the chances of satisfying a human desire as deep as any, the wish to find other beings in the cosmos with whom we might talk things over.

CHAPTER 17

Searching for Life
in the Milky Way Galaxy

W
e have seen that within our own solar system, Mars, Europa, and Titan offer the best hopes for discovering extraterrestrial life, either alive or in fossil form. These three objects present by far the best chances for finding water or another substance capable of providing a liquid solvent within which molecules can meet to carry on life’s work.

Because only these three objects seem likely to have pools or ponds, most astrobiologists limit their hopes of finding life in the solar system to the discovery of primitive forms of life on one or more of them. Pessimists have a reasonable argument, some day to be upheld or refuted by actual exploration, that even though we may well find conditions suitable for life on one or more of this favored threesome, life itself may well prove entirely absent. Either way, the results of our searches on Mars, Europa, and Titan will be laden with significance in judging the prevalence of life in the cosmos. Optimists and pessimists already agree on one conclusion: If we hope to find advanced forms of life—life that consists of creatures larger than the simple, single-celled organisms that appeared first and remain dominant in Earthlife—then we must look far beyond the solar system, to planets that orbit stars other than the Sun.

Once upon a time, we could only speculate about the existence of these planets. Now that well over a hundred exosolar planets have been found, basically similar to Jupiter and Saturn, we may confidently predict that only time and more precise observations separate us from the discovery of Earth-like planets. The final years of the twentieth century seem likely to mark the moment in history when we acquired real evidence for an abundance of habitable worlds throughout the cosmos. Thus the first two terms in the Drake equation, which together measure the numbers of planets orbiting stars that last for billions of years, now imply high rather than low values. The next two terms, however, which describe the probability of finding planets suitable for life, and of life actually springing into existence on such planets, remain nearly as uncertain as they did before the discovery of exosolar planets. Even so, our attempts to estimate these probabilities seem to rest on firmer grounds than our numbers for the final two terms: the probability that life on another world will evolve to produce an intelligent civilization, and the ratio of the average amount of time that such a civilization will survive to the lifetime of the Milky Way galaxy.

For the first
five terms in the Drake equation, we can offer our planetary system and ourselves as a representative example, though we must always invoke the Copernican principle to avoid measuring the cosmos against ourselves, rather than the reverse. When we get to the equation’s final term, however, and attempt to estimate the average lifetime of a civilization once it has acquired the technological capacity to send signals across interstellar distances, we fail to reach an answer even if we take Earth as a guide, since we have yet to determine how long our own civilization will last. We have now possessed interstellar-signaling capacity for nearly a century, ever since powerful radio transmitters began to send messages across Earth’s oceans. Whether we last as a civilization for the next century, through the next millennium, or throughout a thousand centuries depends on factors far beyond our capacity to foresee, though many of the signs seem unfavorable to our long-term survival.

Asking whether our own fate corresponds to the average in the Milky Way takes us into another dimension of speculation, so the final term in the Drake equation, which affects the result as directly as all the others, may be judged just plain unknown. If, in an optimistic assessment, most planetary systems contain at least one object suitable for life, and if life originates on a sensibly high fraction (say one tenth) of those suitable objects, and if intelligent civilizations likewise appear on, perhaps, one tenth of the objects with life, then at some point in the history of the Milky Way’s 100 billion stars, 1 billion locations could produce an intelligent civilization. This enormous number springs, of course, from the fact that our galaxy contains so many stars, most of them much like our Sun. For a pessimistic view of the situation, simply change each the numbers to which we assigned values from one tenth to one chance in ten thousand. Then the billion locations become 1,000, lower by a factor of 1 million.

This makes a major difference. Suppose that an average civilization, qualifying as a civilization by possessing interstellar communications ability, lasts for 10,000 years—approximately one part in a million of the Milky Way’s lifetime. On the optimistic view, a billion places give birth to a civilization at some point in history, so at any representative time, about 1,000 civilizations should be flourishing. The pessimistic view, in contrast, implies that in each representative era about 0.001 civilization should exist, making ourselves a lone and lonely blip that temporarily rises high above the average value.

Which estimate has the greater chance of coming close to the true value? In science, nothing convinces so well as experimental evidence. If we hope to determine the average number of civilizations in the Milky Way, the best scientific approach would measure how many civilizations now exist. The most direct way to perform that feat would survey the entire galaxy, as the cast of television’s
Star Trek
love to do, noting the number and type of each civilization that we encounter, if indeed we find any. (The possibility of an alien-free galaxy makes for boring television, rarely appearing on the small screen.) Unfortunately, this survey lies far outside our current technological capability and budgetary constraints.

Besides, surveying the entire galaxy would take millions of years, if not longer. Consider what a television program about interstellar space surveys would be like if it limited itself by what we know of physical reality. A typical hour would show the crew complaining and bickering, aware that they had come so far yet still had so far to go. “We’ve read all the magazines,” one of them might remark. “We’re sick of each other, and you, Captain, are a great pain in the plethora.” Then, while other crew members sang songs to themselves and still others entered private worlds of madness, a trailing long shot would remind us that the distances to other stars in the Milky Way are millions of times greater than the distances to other planets in the solar system.

Actually, this ratio describes only the distances to the Sun’s closer neighbors, already so distant that their light takes many years to reach us. A full tour of the Milky Way would take us nearly ten thousand times farther. Hollywood films depicting interstellar space flight deal with this all-important issue by ignoring it (
Invasion of the Body Snatchers, 1956
and
1978
), assuming that better rockets or improved understanding of physics will deal with it (
Star Wars
, 1977), or offering intriguing approaches such as freeze-drying astronauts so that they can survive immensely long journeys (
Planet of the Apes
, 1968).

All of these approaches have a certain appeal, and some offer creative possibilities. We may indeed improve our rockets, which can now reach speeds of only about one ten-thousandth of the speed of light, the fastest we can hope to travel according to our current knowledge of physics. Even at the speed of light, however, travel to the nearest stars will take many years, and travel across the Milky Way close to a thousand centuries. Freeze-drying astronauts has some promise, but so long as those on Earth, who presumably will pay for the trip and remain unfrozen, the long passages of time before the astronauts return argues against easy funding. Given our short attention spans, by far the better approach to establishing contact with extraterrestrial civilizations—provided that they exist—appears right here on Earth. All we need do is to wait for them to contact us. This costs far less and can offer the immediate rewards that our society so eagerly craves.

Only one difficulty arises: Why should they? Just what about our planet makes us special to the point that we merit attention from extraterrestrial societies, assuming that they exist? On this point more than any other, humans have consistently violated the Copernican principle. Ask anyone why Earth deserves scrutiny, and you are likely to receive a sharp, angry stare. Almost all conceptions of alien visitors to Earth, as well as a sizable part of religious dogma, rest on the unspoken, obvious conclusion that our planet and our species rank so high on the list of universal marvels that no argument is needed to support the astronomically strange contention that our speck of dust, nearly lost in its Milky Way suburb, somehow stands out like a galactic beacon, not only demanding but also receiving attention on a cosmic scale.

This conclusion springs from the fact that the actual situation appears reversed when we view the cosmos from Earth. Then planetary matters bulk large, while the stars seem tiny points of light. From a quotidian point of view, this makes complete sense. Our success at survival and reproduction, like that of every other organism, has little to do with the cosmos that surrounds us. Among all astronomical objects, only the Sun, and to a much lesser extent the Moon, affect our lives, and their motions repeat with such regularity that they almost seem part of the Earthbound scene. Our human consciousness, formed on Earth from countless encounters with terrestrial creatures and events, understandably renders the extraterrestrial scene as a far-distant backdrop to the important action at center stage. Our error lies in assuming that the backdrop likewise regards ourselves as the center of activity.

Because each of us adopted this erroneous attitude long before our conscious minds attained any dominion or control over our patterns of thinking, we cannot eliminate it entirely from our approach to the cosmos even when we choose to do so. Those who impose the Copernican principle must remain ever vigilant against the murmurings of our reptilian brains, assuring us that we occupy the center of the universe, which naturally directs its attention our way.

When we turn to reports of extraterrestrial visitors to Earth, we must recognize another fallacy of human thought, as omnipresent and self-deceiving as our anti-Copernican prejudices. Human beings trust their memories far more than reality can justify. We do so for the same survival value reasons that we regard Earth as the center of the cosmos. Memories record what we perceive, and we do well to pay attention to this record if we seek to draw conclusions for the future.

Now that we have better means of recording the past, however, we know better than to rely on individual memories for all matters of importance to society. We transcribe congressional debates and laws in print, videotape crime scenes, and make surreptitious audio recordings of criminal activity, because we recognize these media as superior to our own brains for creating a permanent record of past events. One great apparent exception to this rule remains. We continue to accept eyewitness testimony as accurate, or at least probative, in legal proceedings. We do so despite test after test that demonstrates that each of us, despite our best intentions, will fail to remember events accurately, especially when those memories—as they usually do in cases important enough to go to trial—deal with unusual and exciting occurrences. Our legal system accepts eyewitness testimony from long traditition, because of its emotional resonance, and most of all because it often provides the only direct evidence of past events. Nevertheless, every courtroom cry of “That’s the man who held the pistol!” must be weighed against the many demonstrated cases where that was not the man, despite the witness’s sincere belief to the contrary.

If we bear these facts in mind when we analyze reports of unidentified flying objects (UFOs), we can immediately recognize an enormous potential for error. By definition, UFOs are bizarre occurrences, which cause observers to discriminate among familiar and unfamiliar objects on the rarely examined celestial backdrop, and typically require rapid conclusions about these objects before they quickly disappear. Add to this the psychic charge arising from the observer’s belief in having witnessed a tremendously unusual event, and we could hardly find a better textbook example of a situation likely to generate an erroneous memory.

What can we do to obtain data on UFO reports more reliable than eyewitness accounts? In the 1950s, astrophysicist J. Allen Hynek, then a leading Air Force consultant on UFOs, liked to highlight this issue by whipping a miniature camera from his pocket, insisting that if he ever saw a UFO, he would use the camera to obtain valid scientific evidence, because he knew that eyewitness testimony would not qualify. Unfortunately, improvements in technology since that time allow the creation of fake images and video recordings barely distinguishable from honest ones, so that Hynek’s plan would no longer allow us to put our faith in photographic evidence supporting a UFO sighting. In fact, when we consider the interaction of memory’s fragile power with the inventiveness of human con artists, we cannot easily devise a test to discriminate between fact and fancy for any individual UFO sighting.

When we turn to the more modern phenomenon of UFO abductions, the ability of the human psyche to trump reality becomes even more apparent. Although hard numbers cannot be easily obtained, in recent years tens of thousands of people have apparently come to believe that they have been taken aboard an alien spacecraft and subjected to examinations, often of the most humiliating variety. From a calm perspective, stating this claim suffices to refute it as reality. Direct application of the principle of Occam’s razor, which calls for the simplest explanation that fits the alleged facts, leads to the conclusion that these abductions have been imagined, not undergone. Because nearly all of the retellings place the abduction deep in the nighttime, and the majority in the midst of sleep, the likeliest explanation involves the hypnagogic state, the boundary between sleep and waking. For many people, this state brings visual and auditory hallucinations, and sometimes a “waking dream,” in which the person feels conscious but unable to move. These effects pass through the filters of our brains to yield seemingly real memories, capable of arousing unshakable belief in their certainty.