Extraterrestrial Civilizations (38 page)

Etched onto the plaque is informational matter that was decided on by the American astronomers Carl Sagan and Frank Donald Drake. Most of the information would be completely over the heads of all but a very few human beings. It involves details concerning the hydrogen atom, and that information is expressed in binary numbers. It locates the Earth relative to nearby pulsars, giving the periods of the pulsars in binary numbers. Since pulsars are in a particular place only at particular times, and since their rate of rotation slows so that they will have the given rate for only a period of time, this information tells exactly where the Earth has been relative to the rest of the Galaxy at a particular time in cosmic history.

There is also a small diagram of the planets of the Solar system and an indication of
Pioneer 10
itself and the path it took in going through the Solar system.

The most noticeable item on the plaque, though, is a diagrammatic representation of
Pioneer 10
and in front of it, to scale, an unclothed man and woman (drawn by Linda Salzman Sagan, Carl’s wife). The man’s arm is lifted in what (it is hoped) will be interpreted as a gesture of peace.

If an intelligent species should happen to pick up the message, will it be understood? Since it is almost as certain as anything can be that it will be picked up only by some species in a spaceship or a free-world, we can suppose that species will have developed a technology that will possess advanced scientific concepts. They should, therefore, certainly grasp the meaning of the purely scientific symbols. Sagan points out, however, that it is the drawing of the human beings that may puzzle them, since the pictures may be like no form of life they have ever encountered. They may not even interpret the markings as representing a life form.

They will also have
Pioneer 10
itself to study and, in some ways, that may tell them more about Earth and its inhabitants than the plaque will.

But where is
Pioneer 10
taking the plaque?
Pioneer 10
, as it skittered around Jupiter, gained energy from Jupiter’s vast gravitational
field, and by 1984 it will coast past Pluto’s boundary at a speed of 11 kilometers (7 miles) per second. That will be enough to carry it indefinitely away from the Sun, wandering on for billions of years unless it strikes an object large enough to destroy it.

It will take
Pioneer 10
about 80,000 years to recede from us to a distance equal to that of Alpha Centauri. It will not be anywhere near Alpha Centauri at that time, however, for it is not going in that direction.

Pioneer 10
was not aimed with any star in mind, after all. It was aimed at Jupiter in such a way as to give us maximum information about that planet, and whatever direction it took up thereafter, on leaving the Solar system—that was it.

As it happens,
Pioneer 10
will be following a path that will not come close enough to enter the planetary system of any star we can see for at least 10 billion years. Of course it may through sheer accident skim by a free-world some time in its long journey. The chances of even that must surely be exceedingly small, however, and no one seriously expects that
Pioneer 10
will come within the purview of any intelligent species at any time in its long journey.

In that case, why should we have bothered?

In the first place, it was a very small bother. And in the second place, it just might be picked up at some time, and even if those who pick it up are much too far away from us to do anything about it, or if it is picked up at a time long after humanity is extinct, we would nevertheless have made some mark on the Universe.

We would have left behind evidence that once there was an intelligent species on our small world that could manage to put together enough expertise to hurl an object out of our Solar system. There is such a thing as pride!

Finally, we can multiply our chances by sending out more than one message. An identical plaque was placed on
Pioneer 11
, which will eventually leave the Solar system on a track different from that of
Pioneer 10
.

And in 1977, probes were launched on which were included numerous photographs showing widely mixed aspects of life on Earth, together with a recording containing enormously varied sounds produced on Earth.

Obviously, it will be some time before we are in a position to send out messages that are more than passive cartoons, aimed virtually at random.

Furthermore, there is some opposition to the thought of sending out messages at all. The nub of that opposition rests with the question: “Why attract attention?”

Suppose we do announce our presence. Are we not simply inviting civilizations advanced beyond ours, which have hitherto not been aware of our presence, to make for us at full speed and to arrive with the intention of taking over our world, of reducing us to slavery, or of wiping us out?

The chances seem to me to be strongly against that. I have explained earlier in the book why I consider it very likely that civilizations that have advanced beyond our own level of technology will be peaceful. Even if not peaceful, civilizations are very likely confined to their own planetary systems. In the very unlikely case that a civilization is warlike and is also roaming freely through space, it has probably examined all stars and is aware of our presence. Finally, even if it has unaccountably missed us, we have already given ourselves away by our radio broadcasts.

For all these reasons, it makes no difference whether we signal or not, and yet it is hard to answer the unreasoning fears that assume the very worst combination of possibilities. Suppose there
are
civilizations out there as vicious and warlike as we ourselves are at our worst, who
can
move through space freely, who
are
looking for new prey, and who have until now been unaware of us. Shouldn’t we lie low and keep absolutely quiet?

Accepting that argument, should we not, for our own safety, find out as much as we can about these hypothetical monsters even while we are lying low? Shouldn’t we want to know where the danger is, how bad it might be, how best we might defend ourselves, or (if that is impossible) how best we might more effectively hide?

In other words, abandoning any attempt to send messages (at which we are ineffective, in any case) ought we not to make every attempt to
receive
messages? If we do receive a message and decipher it and decide we don’t like what we hear, there is, after all, no reason why we would have to answer it.

Would we, however, know we had come across a signal if we detected it? What ought we to look for?

We might take the optimistic attitude that though we can’t predict what the signals would be, we would recognize them if they were there. The detection of what seemed to be a network of Martian canals was a complete surprise, but was quickly taken as an indication of a high civilization.

We know now, though, that if life signals are obtained from anywhere it will have to be from the planetary systems of other stars (or possibly from automatic probes or free-worlds in interstellar space). The likelihood is that any signals we do get will come from many light-years away, and the question is whether it is reasonable to suppose that signals energetic enough to make themselves felt across such distances could be sent out.

It might be that we should not judge all civilizations by our own. What seems a high energy level to ourselves might not seem high at all to more advanced civilizations. In 1964, the Soviet astronomer N. S. Kardashev suggested that civilizations might exist at three levels. Level I is Earthlike and can dispose of energy intensities of the kind available through the burning of fossil fuels. Level II could tap the entire energy of its star, thus disposing of energy intensities 100 trillion times that of Level I. Level III could tap the entire energy of the galaxy of which it is a part, thus disposing of energy intensities 100 billion times that of Level II.

A signal from a Level-II civilization could easily have enough energy content to be detectable from any part of the galaxy of which it is part. A signal from a Level-Ill civilization could easily have enough energy content to be detectable anywhere in the Universe.

We might dismiss this at once by saying that we detect no signals anywhere but, in the first place, we are not really listening. In the second place, even if the signals forced themselves upon our consciousness, would we recognize them for what they are?

In 1963, for instance, the Dutch-American astronomer Maarten Schmidt (1929–) discovered quasars, extraordinarily bright and distant objects that show irregular variations in brightness. In 1968, the British astronomer Anthony Hewish (1924–) announced the discovery of pulsars, which send out regular pulses of radiation at very short but very slowly lengthening intervals. Beginning in 1971,
certain intense x-ray streams that varied irregularly in intensity were ascribed to black holes.

Could it be that these objects represent the signal beacons of Level-II or Level-III civilizations? To be sure, the variations in intensity seem to be quite irregular in the case of quasars and black holes, and quite regular in the case of pulsars, and in either case don’t seem to have the kind of information that would be of intelligent origin—but may that be merely the result of our own inadequate understanding?

Perhaps! From the conservative position of this book, however, it is an extremely unlikely
perhaps
. We can only say that thus far there is no large-scale phenomenon in the Universe, involving the kind of energy output characteristic in intensity of stars or galaxies, where there is any evidence whatever of intelligent information content. Until such evidence arrives, we must delay a decision.

Of course, a signal might not be a deliberate beacon but the entirely involuntary accompaniment of a civilization’s activities. We are illuminating our cities and highways only for the convenience and safety of human beings, but it turns out to be a signal to any extraterrestrial civilizations that are close enough and attentive enough to note it.

If the Martian canals really existed, they would do so only to supply the Martian civilization with badly needed water for irrigation—but their existence would have signaled us.

In the same way, a more advanced civilization may do something sufficiently enormous to make itself felt at stellar distances.

Freeman J. Dyson suggested that if human beings began to exploit and explore space, they might wish to expand their numbers to the utmost that can be sustained by the Sun’s energy. At the present moment, the Earth stops only a tiny fraction of sunlight, and almost all the solar radiational energy slips past the cool bodies of the Solar system to streak into and through interstellar space. Human beings might therefore eventually break up the various outer bodies of the Solar system to make up a group of free-worlds that will be placed in a spherical shell about the Sun at the distance of the inner edge of the asteroid belt.

All the Sun’s energy would be absorbed and utilized by one or another of the free-worlds. The energy would, of course, be reradiated
into space from the dark side of each of the free-worlds, but only as infrared radiation. Viewed from another star, then, the Sun’s radiation would seem to change its character from one in which a major portion was emitted as visible light to one in which almost all was emitted as infrared. The changeover would take perhaps a couple of centuries, the barest instant of astronomical time.

If, then, from our own Earth we should see some other star, which has been shining steadily as far as our records tell us, suddenly begin to lose brightness and after a while blink out, we can be reasonably sure we have seen intelligence at work.

Well, perhaps—but we haven’t seen anything of the sort as yet.

We must come to the conclusion, then, that (1) we are hopelessly inept at detecting signals and might as well not bother; or that (2) no signals are being sent out and that we might as well not bother; or that (3) signals are being sent out but at much less than heroic energy content, and as a result of much less than heroic civilizational activity, and that in order to detect them we will have to make a considerable effort.

Clearly, we cannot accept the first or second conclusions until we have made an honest attempt at the third.

Then let us consider signals of low-energy content (but high-energy enough to detect) and see what they might be like.

They would have to consist of some phenomenon that could cross vast reaches of space, and these can be divided into three classes: (1) large objects such as plaques, probes, and free-worlds; (2) subatomic particles with mass; (3) subatomic particles without mass.

The large objects we can eliminate at once. They move slowly and are extremely inefficient as carriers of information.

The subatomic particles with mass can be divided into two subclasses, those without electric charge and those with electric charge. Subatomic particles with mass but without electric charge generally move slowly and can be eliminated as impractical for that reason.

Subatomic particles with both mass and electric charge
can
move quickly because they are accelerated by the electromagnetic fields associated with stars and with galaxies as a whole. Therefore, in crossing interstellar and intergalactic spaces, they achieve very nearly the speed of light and, in consequence, enormous energies.

Such subatomic particles do indeed occur everywhere and they
are constantly and eternally bombarding the Earth. We call them cosmic rays.

The difficulty here, though, is that the mere fact that these particles are accelerated by electromagnetic fields means that they experience an attraction or a repulsion and that, in either case, their paths curve. As the particles gain increasing energy, their paths curve more and more slightly, but over vast distances even the slightest curve becomes important. What’s more, a beam of particles is gradually dispersed, since those with more energy are curved less than those with less energy.