Pulsars Not Signals From “Little Green Men”

Press, Volume CVIII, Issue 31762, 20 August 1968, Page 10

Pulsars Not Signals From “Little Green Men”

(By ROBERT C. COWEN, natural science editor of the "Christian Science Monitor.”) A year ago, British radio astronomers began to wonder if they had the electronic equivalent of a note in a bottle drifting in from a trackless sea.

A new antenna system at Cambridge University was picking up cosmic radio pulses so regularly timed that they might be signals from intelligent beings.

Many astronomers now have taken a look at those mysterious pulsars (pulsating radio sources). They have largely squashed the “little green men” theory of intelligent signals.

But the object* remain tantalising and unexplained. And part of their interest for th* layman lie* in what they have shown about the attitude of scientists toward the possibility of contact with alien beings. Discussing thi* during a recent interview, Dr Alan Moffet of the California Institute of Technology, a leading pulsar investigator, said he sees “no need to go beyond a natural explanation.” Yet he consider* the willingness of some British and American astronomers to explore the question of intelligent signal* to be scientifically sensible. It show* that scientists’ thinking to becoming more open to this admittedly far out possibility. Astronomer* now discount the “intelligent signal” explanation in the case of the pulsar* because of the nature of the signals, Dr Moffet explained. They have not shied away from it just because it smacks of science fiction.

So far. seven pulsar* have been found, all within Earth’* galaxy. Six were discovered by Anthony Hewish and others at Cambridge University’s Milliard Radio Astronomy Observatory. Dr George R. Huguenin and J. H. Taylor of Harvard University, in July, reported finding the fifth pulsar near th* Little Dipper. Interval Constant All of the object* emit sharp radio pulse* which recur at interval* ranging from about 0.25 to 1.4 second*. The strength of the slgnel varies erratically from puls* to puls* for any of the** objects. But the interval between pulse* is constant to better than one pert in 10 million. It’* ao precise that scientists at the Arecibo lonospheric Observatory In Puerto Rico suggest it as a new time standard. Astronomers cannot account for this precision. Some think it may be the pulsating of certain kinds of superdense stars. Others wonder is a fast rotating star is sending out a beam of radio noise. Like the blink of a lighthouse beacon, the radio beam would show up as a pulse every time it swept the earth. Dr Moffet said that he’s more concerned with getting better data on the pulsars than with speculation a* to what they are. Rejection Explained “It may be,” he said, “that we can distinguish between hypotheses if we take measurements over long intervals. For example, physically, it might be easier to maintain a constant period with a rotating body than with a pulsating system. So, if we find the pulsing period to be even mor* stable than we now know it to be, we might be able to choose between these two possible types of sources.” However, he noted that astronomer* already know enough to discount the -little green men" theory on rational grounds. He explained that “the pulsars radiate over a wide band of frequencies. This is one reason to doubt they are part of an intelligently made navigational system as someone suggested. "Of course, there’s a certain amount of anthropomorphism in concluding this. If we built such a system, we would go for a narrow fre-

queue? band to conserve power.

Natural Sources “We don’t really know how pulsars are powered. But we assume that, even if you could generate their enormous power artificially, you would want to use narrow band signals to conserve it “On the other hand, many natural phenomena' ‘broadcast’ radio noise with wide frequency bands. It seems reasonable to class pulsars as Ono of them.” Is it possible this might not be anything useful like a navigational system, but simply a signal to attract attention? In that case, might not the broadcasters want to use many frequencies to make it easier for others to get the message? When asked this, Dr Moffet pointed out: “It’s often said that if one were going to design a signalling system to announce your existence to being* on other worlds, you would us* something all technological societies should understand and know about. “Mo»t obviously, you would plek a narrow band of frequencies near th* frequency «t which hydrogen in space naturally emits a well-defined radio noise. Failed Test “This is the most widely occuring frequency in the universe. People will be look-

Ing with narrow band detectors at this frequency and studying the galaxy in different directions. “Using a narrow band carrier near the hydrogen frequency, you would modulate it in a simple on-off manner with a period characterised by, say, pi, or some other natural number known to all.”

Pulsar signals have neither of these characteristics which sstronomers would expect in a recognition signal. In thinking this way, astronomers realise they are using human logic to which aliens might not conform. That’s

why some of them, at first, took seriously th* possibility of intelligent signals when pulsars were discovered. Now this suggestion seems to have been made too hastily. And the responsible astronomers seem a bit embarrassed about it to judge from statements at scientific meetings.

Nevertheless, the episode shows that serious scientists do expect that someday, somehow, men may get positive evidence of intelligent beings on other worlds. And scientists are not a bit embarrassed about thinking that