Broca's Brain (44 page)

I wonder how many of our present debates and most celebrated theories will appear, from the vantage point of the year 2049, marked by shoddy observations, indifferent intellectual powers or inadequate physical insight. I have the sense that we are today more self-critical than scientists were in 1899; that because of the larger population of astronomers, we check each other’s results more often; and that, in part because of the existence of organizations like the American Astronomical Society, the standards of exchange and discussion of results have risen significantly. I hope our colleagues of 2049 will agree.

The major advance between 1899 and 1974 must be considered technological. But in 1899 the world’s largest refractor had been built. It is still the world’s largest refractor. A reflector of 100-inch aperture was beginning to be considered. We have improved on that aperture only by a factor of two in the intervening years. But what would our colleagues of 1899—living after Hertz but before Marconi—have made of the Arecibo Observatory, or the Very Large Array, or Very Long Baseline Interferometry (VLBI)? Or checking out the debate on the period of rotation of Mercury by radar Doppler spectroscopy? Or testing the nature of the lunar surface by returning some of it to Earth? Or pursuing
the problem of the nature and habitability of Mars by orbiting it for a year and returning 7,200 photographs of it, each of higher quality than the best 1899 photographs of the Moon? Or landing on the planet with imaging systems, microbiology experimentation, seismometers and gas chromatograph/mass spectrometers, which did not even vaguely exist in 1899? Or testing cosmological models by orbital ultraviolet spectroscopy of interstellar deuterium—when neither the models to be tested nor the existence of the atom that tests it were known in 1899, much less the technique of observation?

It is clear that in the past seventy-five years American and world astronomy has moved enormously beyond even the most romantic speculations of the late-Victorian astronomers. And in the next seventy-five years? It is possible to make pedestrian predictions. We will have completely examined the electromagnetic spectrum from rather short gamma rays to rather long radio waves. We will have sent unmanned spacecraft to all of the planets and most of the satellites in the solar system. We will have launched spacecraft into the Sun to do experimental stellar structure, beginning perhaps—because of the low temperatures—with the sunspots. Hale would have appreciated that. I think it possible that seventy-five years from now, we will have launched subrelativistic spacecraft—traveling at about 0.1 the speed of light—to the nearby stars. Among other benefits, such missions would permit direct examination of the interstellar medium and give us a longer baseline for VLBI than many are thinking of today. We will have to invent some new superlative to succeed “very”—perhaps “ultra.” The nature of pulsars, quasars and black holes should by then be well in hand, as well as the answers to some of the deepest cosmological questions. It is even possible that we will have opened up a regular communications channel with civilizations on planets of other stars, and that the cutting edge of astronomy as well as many other sciences will come from a kind of
Encyclopaedia Galactica
, transmitted at very high bit rates to some immense array of radio telescopes.

But in reading the astronomy of seventy-five years ago, I think it likely that, except for interstellar contact, these achievements, while interesting, will be considered rather old-fashioned astronomy, and that the real frontiers and the fundamental excitement of the science will be in areas that depend on new physics and new technology, which we can today at best dimly glimpse.

THROUGH ALL
of our history we have pondered the stars and mused whether humanity is unique or if, somewhere else in the dark of the night sky, there are other beings who contemplate and wonder as we do, fellow thinkers in the cosmos. Such beings might view themselves and the universe differently. Somewhere else there might be very exotic biologies and technologies and societies. In a cosmic setting vast and old beyond ordinary human understanding, we are a little lonely; and we ponder the ultimate significance, if any, of our tiny but exquisite blue planet. The search for extraterrestrial intelligence is the search for a generally acceptable cosmic context for the human species. In the deepest sense,
the search for extraterrestrial intelligence is a search for ourselves.

In the last few years—in one-millionth the lifetime of our species on this planet—we have achieved an extraordinary technological capability which enables us to seek out unimaginably distant civilizations even if they are no more advanced than we. That capability is called radio astronomy and involves single radio telescopes, collections or arrays of radio telescopes, sensitive radio detectors, advanced computers for processing received data, and the imagination and skill of dedicated scientists. Radio astronomy has in the last decade opened a new window on the physical universe. It may also, if we are wise enough to make the effort, cast a profound light on the biological universe.

Some scientists working on the question of extraterrestrial intelligence, myself among them, have attempted to estimate the number of advanced technical civilizations—defined operationally as societies capable of radio astronomy—in the Milky Way Galaxy. Such estimates are little better than guesses. They require assigning numerical values to quantities such as the numbers and ages of stars; the abundance of planetary systems and the likelihood of the origin of life, which we know less well; and the probability of the evolution of intelligent life and the lifetime of technical civilizations, about which we know very little indeed.

When we do the arithmetic, the sorts of numbers we come up with are, characteristically, around a million technical civilizations. A million civilizations is a breath-takingly large number, and it is exhilarating to imagine the diversity, lifestyles and commerce of those million worlds. But the Milky Way Galaxy contains some 250 billion stars, and even with a million civilizations, less than one star in 200,000 would have a planet inhabited by an advanced civilization. Since we have little idea which stars are likely candidates, we will have to examine a very large number of them. Such considerations suggest that the quest for extraterrestrial intelligence may require a significant effort.

Despite claims about ancient astronauts and unidentified
flying objects, there is no firm evidence for past visitations of the Earth by other civilizations (see
Chapters 5
and
6
). We are restricted to remote signaling and, of the long-distance techniques available to our technology, radio is by far the best. Radio telescopes are relatively inexpensive; radio signals travel at the speed of light, faster than which nothing can go; and the use of radio for communication is not a short-sighted or anthropocentric activity. Radio represents a large part of the electromagnetic spectrum, and any technical civilization anywhere in the Galaxy will have discovered radio early—just as in the last few centuries we have explored the entire electromagnetic spectrum from short gamma rays to very long radio waves. Advanced civilizations might very well use some other means of communication with their peers. But if they wish to communicate with backward or emerging civilizations, there are only a few obvious methods, the chief of which is radio.

The first serious attempt to listen for possible radio signals from other civilizations was carried out at the National Radio Astronomy Observatory in Greenbank, West Virginia, in 1959 and 1960. It was organized by Frank Drake, now at Cornell University, and was called Project Ozma, after the princess of the Land of Oz, a place very exotic, very distant and very difficult to reach, Drake examined two nearby stars, Epsilon Eridani and Tau Ceti, for a few weeks with negative results. Positive results would have been astonishing because as we have seen, even rather optimistic estimates of the number of technical civilizations in the Galaxy imply that several hundred thousand stars must be examined in order to achieve success by random stellar selection.

Since Project Ozma, there have been six or eight other such programs, all at a rather modest level, in the United States, Canada and the Soviet Union. All results have been negative. The total number of individual stars examined to date in this way is less than a thousand. We have performed something like one tenth of one percent of the required effort.

However, there are signs that much more serious
efforts may be mustered in the reasonably near future. All the observing programs to date have involved quite tiny amounts of time on large telescopes, or when large amounts of time have been committed, only very small radio telescopes could be used. A comprehensive examination of the problem was recently made by a NASA committee chaired by Philip Morrison of the Massachusetts Institute of Technology. The committee identified a wide range of options, including new (and expensive) giant ground-based and spaceborne radio telescopes. It also pointed out that major progress can be made at modest cost by the development of more sensitive radio receivers and of ingenious computerized data-processing systems. In the Soviet Union there is a state commission devoted to organizing a search for extraterrestrial intelligence, and the large RATAN-600 radio telescope in the Caucasus, recently completed, is devoted part-time to this effort. Hand in hand with the recent spectacular advances in radio technology, there has been a dramatic increase in the scientific and public respectability of the entire subject of extraterrestrial life. A clear sign of the new attitude is the Viking missions to Mars, which are to a significant extent dedicated to the search for life on another planet.

But along with the burgeoning dedication to a serious search, a slightly negative note has emerged which is nevertheless very interesting. A few scientists have lately asked a curious question: If extraterrestrial intelligence is abundant, why have we not already seen its manifestations? Think of the advances by our own technical civilization in the past ten thousand years and imagine such advances continued over millions or billions of years more. If only a tiny fraction of advanced civilizations are millions or billions of years more advanced than ours, why have they not produced artifacts, devices or even industrial pollution of such magnitude that we would have detected it? Why have they not restructured the entire Galaxy for their convenience?

Skeptics also ask why there is no clear evidence of extraterrestrial visits to Earth. We have already launched slow and modest interstellar spacecraft. A society more
advanced than ours should be able to ply the spaces between the stars conveniently if not effortlessly. Over millions of years such societies should have established colonies, which might themselves launch interstellar expeditions. Why are they not here? The temptation is to deduce that there are at most a few advanced extraterrestrial civilizations—either because statistically we are one of the first technical civilizations to have emerged or because it is the fate of all such civilizations to destroy themselves before they are much further along than we.

It seems to me that such despair is quite premature. All such arguments depend on our correctly surmising the intentions of beings far more advanced than ourselves, and when examined more closely I think these arguments reveal a range of interesting human conceits. Why do we expect that it will be easy to recognize the manifestations of very advanced civilizations? Is our situation not closer to that of members of an isolated society in the Amazon basin, say, who lack the tools to detect the powerful international radio and television traffic that is all around them? Also, there is a wide range of incompletely understood phenomena in astronomy. Might the modulation of pulsars or the energy source of quasars, for example, have a technological origin? Or perhaps there is a galactic ethic of noninterference with backward or emerging civilizations. Perhaps there is a waiting time before contact is considered appropriate, so as to give us a fair opportunity to destroy ourselves first, if we are so inclined. Perhaps all societies significantly more advanced than our own have achieved an effective personal immortality and lose the motivation for interstellar gallivanting, which may, for all we know, be a typical urge only of adolescent civilizations. Perhaps mature civilizations do not wish to pollute the cosmos. There is a very long list of such “perhapses,” few of which we are in a position to evaluate with any degree of assurance.

The question of extraterrestrial civilizations seems to me entirely open. Personally, I think it far more difficult to understand a universe in which we are the only
technological civilization, or one of a very few, than to conceive of a cosmos brimming over with intelligent life. Many aspects of the problem are, fortunately, amenable to experimental verification. We can search for planets of other stars, seek simple forms of life on such nearby planets as Mars, and perform more extensive laboratory studies on the chemistry of the origin of life. We can investigate more deeply the evolution of organisms and societies. The problem cries out for a long-term, open-minded, systematic search, with nature as the only arbiter of what is or is not likely.