Cosmic Connection (25 page)

The change in the climate of opinion about extraterrestrial life was reflected in 1971 by a scientific conference held in Byurakan, Soviet Armenia, and sponsored jointly by the Soviet Academy of Sciences of the U.S.S.R. and the National Academy of Sciences of the United States. I had the privilege of chairing the U.S. delegation to this meeting. The participants represented astronomy, physics, mathematics, biology, chemistry, archaeology, anthropology, history, electronics, computer technology, and cryptography. The group, which included two skeptical Nobel laureates, was marked for its crossing of national as well as disciplinary boundaries. The conference concluded that the chances of there being extraterrestrial communicative societies and our present technological ability to contact them were both sufficiently high that a serious search was warranted. Some of the specific conclusions that were reached were these:

1. The striking discoveries of recent years in the fields of astronomy, biology, computer science and radiophysics have transferred some of the problems of extraterrestrial civilizations and their detection from the realm of speculation to a new realm of experiment and observation. For the first time in human history, it has become possible to make serious and detailed experimental investigations of this fundamental and important problem.

2. This problem may prove to be of profound significance for the future development of Mankind. If extraterrestrial civilizations are ever discovered, the affect on human scientific and technological capabilities will be immense, and the discovery can positively influence the whole future of Man. The practical and philosophical significance of a successful contact with an extraterrestrial civilization would be so enormous as to justify the expenditure of substantial efforts. The consequences of such a discovery would greatly add to the total of human knowledge.

3. The technological and scientific resources of our planet are already large enough to permit us to begin investigations directed towards the search for extraterrestrial intelligence. As a rule, such studies should provide important scientific results even when specific searches for extraterrestrial intelligence do not succeed. At present, these investigations can be carried out effectively in the various countries by their own scientific institutions. Even at this early stage, however, it would be useful to discuss and coordinate specific programs of research and to exchange scientific information. In the future, it would be desirable to combine the efforts of investigators in various countries to achieve the experimental and observational objectives. It seems to us appropriate that the search for extraterrestrial intelligence should be made by representatives of the whole of mankind.

4. Various modes of search for extraterrestrial intelligence were discussed in detail at the Conference. The realization of the most elaborate of these proposals would require considerable time and effort and an expenditure of funds comparable to the funds devoted to space and nuclear research. Useful searches can, however, also be initiated at a very modest scale.

5. The Conference participants consider highly valuable present and forthcoming space-vehicle experiments directed towards searching for life on the other planets of our solar system. They recommend the continuation and strengthening of work in such areas as prebiological organic chemistry, searches for extrasolar planetary systems, and evolutionary biology, which bear sharply on the problem.

6. The Conference recommends the initiation of specific new investigations directed towards modes of search for signals.
(The complete Proceedings of the conference are published as
Communication with Extraterrestrial Intelligence
, Carl Sagan, ed., Cambridge, Massachusetts, The M.I.T. Press, 1973.)

Another sign of the increasing acceptability of the search for extraterrestrial intelligence is the recommendations of the Astronomy Survey Committee of the U. S. National Academy of Sciences, which had been asked to summarize the needs of astronomy in the decade of the 1970s. The Committee’s report was the first such national report on the future of astronomy to lay stress on the search for extraterrestrial intelligence–as a possibly important by-product of astronomical research in the near future and as a justification for the construction of large radio telescopes.

Nearer to home, there is an accelerating set of laboratory studies of the origin of life on Earth. If the origin of life on Earth turns out to have been exceedingly “easy,” the chances of life elsewhere are correspondingly high.

There is also a concerted effort in the United States–Project Viking–to land instrumented payloads on the surface of Mars to search for indigenous life forms.

The idea of extraterrestrial life is an idea whose time has come.

B
y far the cheapest way of communicating with the Earth, if you’re a representative of an advanced extraterrestrial civilization, is by radio. A single bit of radio information, sent winging across space to the Earth, would cost far less than a penny. A radio search for extraterrestrial intelligence seems, therefore, a very reasonable place for us to begin. But should we not examine other possibilities closer to home? Wouldn’t we look silly if we expended a major effort listening for radio messages or searching for life on Mars if, all the while, there was here on Earth evidence of extraterrestrial life?

There are two hypotheses of this sort that have gained a following in the popular literature. The first postulates that the Earth is today being visited by spacecraft from other worlds–this is the extraterrestrial flying saucer or unidentified flying object (UFO) hypothesis. The second also postulates that the Earth has been visited by such spacecraft, but in the past, before written history.

The extraterrestrial hypothesis of UFO origins is a complex subject, powerfully dependent on the reliability of witnesses. A comprehensive discussion of this problem has recently been published in
UFO’s: A Scientific Debate
(Carl Sagan and Thornton Page, editors, Ithaca, N.Y., Cornell University Press, 1972), in which all sides of the subject have been aired. My own view is that there are no cases that are simultaneously very reliable (reported independently by a large number of witnesses) and very exotic (not explicable in terms of reasonably postulated phenomena–as a strange moving light could be a searchlight from a weather airplane or a military aerial refueling operation). There are no reliably reported cases of strange machines landing and taking off, for example.

There is another approach to the extraterrestrial hypothesis of UFO origins. This assessment depends on a large number of factors about which we know little, and a few about which we know literally nothing. I want to make some crude numerical estimate of the probability that we are frequently visited by extraterrestrial beings.

Now, there is a range of hypotheses that can be examined in such a way. Let me give a simple example: Consider the Santa Claus hypothesis, which maintains that, in a period of eight hours or so on December 24-25 of each year, an out-sized elf visits one hundred million homes in the United States. This is an interesting and widely discussed hypothesis. Some strong emotions ride on it, and it is argued that at least it does no harm.

We can do some calculations. Suppose that the elf in question spends one second per house. This isn’t quite the usual picture–“Ho, Ho, Ho,” and so on–but imagine that he is terribly efficient and very speedy; that would explain why nobody ever sees him very much–only one second per house, after all. With a hundred million houses he has to spend three years just filling stockings. I have assumed he spends no time at all in going from house to house. Even with relativistic reindeer, the time spent in a hundred million houses is three years and not eight hours. This is an example of hypothesis-testing independent of reindeer propulsion mechanisms or debates on the origins of elves. We examine the hypothesis itself, making very straightforward assumptions, and derive a result inconsistent with the hypothesis by many orders of magnitude. We would then suggest that the hypothesis is untenable.

We can make a similar examination, but with greater uncertainty, of the extraterrestrial hypothesis that holds that a wide range of UFOs viewed on the planet Earth are space vehicles from planets of other stars. The report rates, at least in recent years, have been several per day, at the very least. I will not make that assumption. I will make the much more conservative assumption that one such report per year corresponds to a true interstellar visitation. Let’s see what this implies.

We have to have some feeling for the number, N, of extant technical civilizations in the Galaxy–that is, civilizations vastly in advance of our own, civilizations that are able, by whatever means, to perform interstellar space flight. (While the means are difficult, they don’t enter into this discussion, just as reindeer propulsion mechanisms don’t affect our discussion of the Santa Claus hypothesis.)

An attempt has been made to specify explicitly the factors that enter a determination of the number of such technical civilizations in the Galaxy. I will not here run through what numbers have been assigned to the various quantities involved–it’s a multiplication of many probabilities, and the likelihood that we can make a good judgment decreases as we proceed down the list. N depends first on the mean rate at which stars are formed in the Galaxy, a number that is known reasonably well. It depends on the number of stars that have planets, which is less well known, but there are some data on that. It depends on the fraction of such planets that are so suitably located with respect to their star that the environment is a feasible one for the origin of life. It depends on the fraction of such otherwise feasible planets on which the origin of life, in fact, occurs. It depends on the fraction of
those
planets on which the origin of life occurs in which, after life has arisen, an intelligent form comes into being. It depends on the fraction of
those
planets in which intelligent forms have arisen that evolve a technical civilization substantially in advance of our own. And it depends on the average lifetime of such a technical civilization.

It is clear that we are rapidly running out of examples as we go farther and farther along. We have many stars, but only one instance of the origin of life, and only a very limited number–some would say only one–of instances of the evolution of intelligent beings and technical civilizations on this planet. And we have no cases whatever to make a judgment on the mean lifetime of a technical civilization. Nevertheless, there is an entertainment that some of us have been engaged in, making our best estimates about these numbers and coming out with a value of N. The result that emerges is that N roughly equals one tenth the average lifetime of a technical civilization in years.

If we put in a number like ten million (10
⁷
) years for the average lifetime of advanced technical civilizations, we come out with a number for such technical civilizations in the Galaxy of about a million (10
⁶
)–that is, a million other stars with planets on which today there are advanced civilizations. This is quite a difficult calculation to do accurately. The choice of ten million years for the average lifetime of a technical civilization is rather optimistic. But let’s take these optimistic numbers and see where they lead us.

Let’s assume that each of these million technical civilizations launches Q interstellar space vehicles a year, so that 10
⁶
Q interstellar space vehicles are launched per year. Let’s assume that there’s only one contact made per journey. In the steady-state situation, there are something like 10
⁶
Q arrivals somewhere or other per year. Now, there surely are something like 10
¹⁰
interesting places in the Galaxy to go visit (we have several times 10
¹¹
stars) and, therefore, an average of 1/10
⁴
=10
^–4
arrivals at a given interesting place (let’s say a planet) per year. So if only one UFO is to visit the Earth each year, we can calculate what mean launch rate is required at each of these million worlds. The number turns out to be ten thousand launches per year per civilization, and ten billion launches in the Galaxy per year. This seems excessive. Even if we imagine a civilization much more advanced than ours, to launch ten thousand such vehicles for only one to appear here is probably asking too much. And if we were more pessimistic on the lifetime of advanced civilizations, we would require a proportionately larger launch rate. But as the lifetime decreases, the probability that a civilization would develop interstellar flight very likely decreases as well.

There is a related point made by the American physicist Hong-Yee Chiu; he takes more than one UFO arriving at Earth per year, but his argument follows along the same lines as the one I have just presented. He calculates the total mass of metals involved in all of these space vehicles during this history of the Galaxy. The vehicle has to be of some size–it should be bigger than the Apollo capsule, let’s say–and we can calculate how much metal is required. It turns out that the total mass of half a million stars has to be processed and all their metals extracted. Or if we extend the argument and assume that only the outer few hundred miles or so of stars like the Sun can be mined by advanced technologies (farther in, it’s too hot), we find that two billion such stars must be processed, or about 1 percent of the stars in the Galaxy. This also sounds unlikely.

Now you may say, “Well, that’s a very parochial approach; maybe they have plastic spaceships.” Yes, I suppose that’s possible. But the plastic has to come from somewhere, and plastics vs. metals changes the conclusions very little. This calculation gives some feeling for the magnitude of the task when we are asked to believe that there are routine and frequent interstellar visits to our planet.

What about possible counterarguments? For example, it might be argued that we are the object of special attention–we have just developed all sorts of signs of civilization and high intelligence like nuclear weapons, and maybe, therefore, we are of particular interest to interstellar anthropologists. Perhaps. But we have only signaled the presence of our technical civilization in the past few decades. The news can be only some tens of light-years from us. Also, all the anthropologists in the world do not converge on the Andaman Islands because the fish net has just been invented there. There are a few fish net specialists and a few Andaman specialists; and these guys say, “Well, there’s something terrific going on in the Andaman Islands. I’ve got to spend a year there right away because if I don’t go now, I’ll miss out.” But the pottery experts and the specialists in Australian aborigines don’t pack up their bags and leave for the Indian Ocean.