Extraterrestrial Civilizations (40 page)

During World War II, the development of radar changed everything. Radar made use of microwaves so that microwave technology advanced rapidly, and after the war, radio astronomy quickly became a giant, revolutionizing the science as it had been revolutionized by Galileo’s optical telescope 3½ centuries before.

In just a few decades, radio telescopes have been built that can detect microwaves far more delicately than light can be detected. Sources of microwave radiation could be detected at distances too great for us to make out light radiation of anything like equivalent
energy. In fact, we can right now detect microwaves from any star in the Galaxy, even though those microwaves are sent out with no more energy than we ourselves could dispose of.

Then, too, the sources of microwaves can be located with great precision, and the varieties of microwaves can be differentiated with great ease. Every molecule emits or absorbs its own specific wavelength, so that the chemical constitution of interstellar gas clouds can be determined with great precision. Microwaves are not blanked out by background radiation. In most parts of the sky, microwaves are not radiated with the intensity of light, and even where microwaves are plentiful, it would be easy for a civilization to send out a specific wavelength that would be far stronger than the natural background
for that wavelength
.

It amounts to this: If any civilization is trying to send out messages, it would surely come to the conclusion that microwaves are a better, cheaper, and more natural medium for those messages than light—or, in fact, than anything.

We finally have what looks like the answer. To send, or receive, messages across the interstellar gulfs, we must make use of microwaves.

But at what energy level, or wavelength, ought we to expect the message to come? Receivers can be tuned to receive some specific wavelength, and if the message is being sent at another wavelength, it will be missed. On the other hand, to try to tune in all possible wavelengths would enormously increase the difficulty and expense of listening. But can we read the extraterrestrial mind and guess the wavelength it would choose to use?

During World War II, the Dutch astronomer Hendrick Chistoffell Van de Hulst (1918–), unable to make observations under the Nazi occupation, did some pen-and-paper calculations that showed that cold hydrogen atoms would sometimes undergo a change in configuration that would result in the emission of a microwave photon that was 21 centimeters (8.3 inches) in wavelength.

The individual hydrogen atom undergoes the change only very rarely but, considering all the hydrogen atoms in space, great numbers are undergoing the change at every moment, so that if Van de Hulst’s calculations were correct, the microwaves produced by hydrogen atoms should be detectable. In 1951, the American physicist
Edward Mills Purcell (1912–) did detect them.

The hydrogen atom is predominant in the space between the stars, and the 21-centimeter wavelength is therefore a universal radiation that would be received anywhere. Any civilization that had reached our technological level would certainly be radio astronomers, and we can be certain they would have instruments equipped to receive the 21-centimeter wavelength even if they bothered with nothing else. Surely they would transmit messages over a wavelength they could themselves receive and one that they would be certain that all other civilizations would be tuned to.

In 1959, therefore, the American physicist Philip Morrison and the Italian physicist Giuseppe Cocconi (1914–) suggested that if signals from extraterrestrials were searched for, they should be searched for at 21-centimeter wavelengths.

That is the microwave wavelength, however, in which the background radiation is strongest and potentially the most obscuring—particularly in the region of the Milky Way. There is some feeling, therefore, that we ought to look somewhere else, perhaps at 42 centimeters or 10.5 centimeters, since doubling or halving the obvious choice is the simplest way of using 21 centimeters as the basis for the message without using that wavelength itself.

Another suggestion is to make use of hydroxyl, the 2-atom combination of hydrogen and oxygen, which, next to hydrogen itself, is the most widespread emitter of microwaves in interstellar space. Its microwave emission has a wavelength of 17 centimeters (6.7 inches).

Since hydrogen and hydroxyl together make water, the stretch of microwaves from 17 to 21 centimeters in wavelength is sometimes called the waterhole. The name is particularly apt, because the hope is that different civilizations will send and receive messages in this region as different species of animals come to drink at literal water-holes on Earth.

In 1960, the first real attempt was made to listen to the 21-centimeter wavelength in the sky in the hope of detecting messages from extraterrestrial civilization. It was carried through in the United States under the direction of Frank Drake, who called it Project Ozma. Ozma was Princess of Oz, the distant land in the sky of the well-known children’s adventure series. After all, the astronomers were trying to gain evidence of occupied lands even farther in the sky than Oz is.

The listening began at 4
A.M
. on April 8, 1960, with absolutely no publicity, since the astronomers feared ridicule. It continued for a total of 150 hours through July, and the project then came to an end. The listeners were on the alert for anything with a very narrow range of wavelengths that seemed to flicker in a way that was neither quite regular nor quite random. They detected nothing of the sort.

Since Project Ozma, there have been six or eight other such programs, all at a level even more modest than the first, in the United States, in Canada, and in the Soviet Union. There have been no positive results, but the fact is that the search has been very brief and superficial so far.

Astronomers remain alive to the possibility of accidental discoveries, of course. When, in 1967, pulsars (very tiny, very dense, very rapidly rotating stars that were remnants of collapse following supernova explosions) were discovered, for just a short while the surprising detection of pulses of microwaves gave the astronomers concerned an eerie feeling that messages of intelligent origin were being received. They referred to it as the LGM (“little green men”) phenomenon. The pulses quickly proved far too regular to be carrying a message, however, and less dramatic explanations were found.

If the search for messages from extraterrestrial civilizations is to be carried through with some reasonable hope of success, however, far more time must be spent than was the case in Project Ozma; far more stars must be studied, far more elaborate equipment must be used. In short, a very expensive project must be set up.

In 1971, a NASA group under Bernard Oliver suggested what has come to be called Project Cyclops.

This would be a large array of radio telescopes,
^*
each 100 meters (109 yards) in diameter, and each adjusted for reception of microwaves in the waterhole region.

The array would consist of 1,026 such radio telescopes in rank and file, all of them steered in unison by a computerized electronic
system. The entire array working together would be equivalent to a single radio telescope some 10 kilometers (6.2 miles) across.

The array would be capable of detecting something as weak as Earth’s inadvertent leakage of microwaves even from a distance of 100 light-years, while the deliberately emitted message beacon of another civilization could be detected at a distance of at least 1,000 light-years.

Earth’s surface may not be the best place for it. If it could be built in space, or, better yet, on the far side of the Moon, it would be insulated from most or all of the background of Earth’s own microwave noise.

Project Cyclops would not be easy to construct and certainly not cheap. Estimates are that the construction and maintenance of the array and the search itself would cost anywhere from $10 to $50 billion, even allowing for the fact that eventually the listening will be completely computerized and will not take much in the way of people-hours.

Anything that could be done to make the search simpler and quicker would be helpful, therefore. There might be places in the sky, for instance, where it would pay us to search first because they are more likely sources of messages than other places are.

Where might these places be?

First, the best place to search is in the neighborhood of some star where a planetary civilization with copious energy at its disposal might exist. (There might be, to be sure, signals being sent out by free-worlds or automatic probes that are closer to us than any star, but we have no way of knowing where such objects are and therefore no particular target to aim at.)

Second, the objective should be a nearby star rather than a distant star, since, all things being equal, the microwave beam will be more intense and easier to detect the closer the planetary system from which it starts.

Third, the objective should be a Sunlike star, since it is there we expect habitable planets might exist.

Fourth, the first objectives should be single stars, since, even though it seems that binary stars may still have habitable planets circling them, the chances are perhaps greater in the case of single stars.

As it happens, there are just seven Sunlike single stars within 2 dozen light-years of us, and they are:

None of these stars has a familiar name, for those that do are generally the brightest, which are too large and short lived to be suitable for civilizations.

Stars that are visible to the unaided eye, even if they are not outstandingly bright, are generally named for the constellation in which they are found. Sometimes they are listed in order of brightness, or position, by the use of Greek letters (alpha, beta, gamma, delta, epsilon, zeta, and so on) or by Arabic numerals.

The stars in the table above are from the constellations Eridanus (the River), Cetus (the Whale), Draco (the Dragon), Pavo (the Peacock), Hydrus (the Water Snake), and Tucana (the Toucan).

Of the seven stars listed in the table, three—Delta Pavonis, Beta Hydri, and Zeta Tucanae—are located so far south in the sky as to be invisible from the northern climes where astronomy is most advanced and where complex equipment exists in the greatest profusion. As for 82 Eridani, that is not too far south to be visible, but it is apt to be too near the horizon for complete comfort.

The three very best targets, then, are Epsilon Eridani, Tau Ceti, and Sigma Draconis. Project Ozma, at the suggestion of the Russian-American astronomer Otto Struve, concentrated on Epsilon Eridani and Tau Ceti.

Although these seven stars, and particularly the three northern stars, are the obvious targets for the first phase of the search, we should not quit if the results are negative. If there are seven prime targets within 23 light-years, there would be about 500,000 altogether within the 1,000-light-year reach of the Project Cyclops array.

Ideally, we should listen to all of them. In fact, before we really give up hope, we should scan the entire sky, just in case civilizations are present in the neighborhood of surprising stars—or just in case we get signals from probes or free-worlds that are fairly close to us without our being aware of it.

We should even search wavelength ranges outside the waterhole, just in case.

Yet one must ask: Why ought humanity to engage in the task of monitoring space for signals from extraterrestrial civilizations? Why should we spend tens of billions of dollars when the chances are that we may find nothing at all?

After all, what if, despite all my reasoning in this book, there are no extraterrestrial civilizations?

—Or if there are, that there are none so close to us that we can detect their signals?

—Or if there are, that they are not signaling?

—Or if they are, that they are doing so in a way that will elude us altogether?

—Or if it doesn’t, that the signals we receive will be uninterpretable?

Any of these things is possible, so let us assume the worst and suppose that despite all our efforts, we end up with no recognizable signals at all from anywhere.

In that case, will we really have wasted much money?

Perhaps not. Suppose that the labor of building Project Cyclops and the task of searching the sky takes 20 years altogether and costs $100 billion. That is $5 billion a year in a world in which the various nations spend a total of $400 billion a year on armaments.

And whereas the money spent on armaments only stimulates hatred and fear and increases steadily the chance that the nations of the Earth will wipe out each other and, perhaps, all humanity, the search for extraterrestrial intelligence is something that would surely have a uniting effect on us all. The mere thought of other civilizations advanced beyond our own, of a Galaxy full of such civilizations, can’t
help but emphasize the pettiness of our own quarrels and shame us into more serious attempts at cooperation. And if the failure of the search should cause us to suspect that we are, after all, the only civilization in the Galaxy, might that not increase the sense of the preciousness of our world and ourselves and make us more reluctant to risk it all in childish quarrels?

But will the money be wasted at all if we end up with nothing?

In the first place, the very attempt to construct the equipment for Project Cyclops will succeed in teaching us a great deal about radiotelescopy and will undoubtedly advance the state of the art greatly even before so much as a single observation of the heavens is made.