This is not where you would want to transmit or receive. At the high-frequency end, there is another source of noise, intrinsic to the quantum nature of radio detectors. And in the middle there is a broad region where the noise is low, and this is the window in which it makes sense to transmit. In this window there are certain spectral lines, for example, of atomic hydrogen, the most abundant atom in the universe, at specific frequencies. So for this reason there is now a very sophisticated search program going on at Harvard, in Massachusetts, a cooperative project with Harvard University and the Planetary Society, a hundred-thousand- member worldwide organization, and it is remarkable that dues and contributions to a private organization are able to maintain by far the most sophisticated search for extraterrestrial intelligence yet attempted. [4]
This illustration might convey a sense of how a success would be noted. The slanting line indicates a very weak signal from an extraterrestrial source. You listen at many frequencies for a while and see if there's anything happening. The Planetary Society system was recently upgraded, so that 8.4 million separate channels are being listened to simultaneously. The antenna points to some part of the sky. And some places have peaks. They may be due to radio interference on the Earth, satellites in Earth orbit, automobile ignitions, diathermy machines. But each of those has a particular kind of signature, and it is possible to imagine signals that don't look like any of those things, which the computer immediately would cull out of the noise, leaving no doubt that this was an artificial signal of extraterrestrial origin, even if we had no opportunity, no ability, to understand what it meant.
Now, as I said, the expectation is that they send and we, newly emerged, the youngest communicative civilization in the Galaxy, we listen. Not the other way around.
Let me stress that this is the one respect in which our civilization is probably unique in the Galaxy. No one even slightly more ignorant can communicate at all. Let me say this in a better way: A civilization only a few decades behind us would not have radio astronomy and therefore could not tumble to this technique. Or maybe they could tumble to it, but they couldn't manifest it. And anyone, therefore, whom we hear from is likely to be ahead of us, because if they're even a little bit behind us, they can't communicate at all.
So the most likely situation is communications from beings vastly more advanced than us. And this therefore raises the ques-
tion, could we possibly understand what they're saying? What we have to remember here is that if this is an intentional message from them to us, then they can make it easy. They can make allowances for civilizations. And if they do not choose to do that, then we will not understand the message.
Maybe you would say advanced civilizations communicate with each other by zeta waves. And I'd say, 'What is a zeta wave?' And you reply, 'It is something fantastic for communication that I can't give you any details about, because it won't be invented for another five thousand years.' Well, that's wonderful, and if those fellows can communicate with zeta waves, that's terrific. But if they wish to communicate with us, they will have to wheel out some ancient, creaking radio telescope from the technology museum and use it, because that is all that young civilizations will be able to understand and detect.
Now, suppose we get a message. What would it be like? Here is a possibility: There would be a powerful beacon or announcement signal, something that makes it very clear that we are unambiguously receiving a message from an advanced civilization. It might, for example, be highly monochromatic; that is, a very narrow radio frequency band pass, and/or it might be a sequence of pulses that could not possibly be of natural origin. For example, a sequence of prime numbers, numbers divisible only by 1 and themselves-1, 2, 3, 5, 7, 11, 13, 17, 19, and so on. There is no natural process that could produce such numbers.
Then, having established unambiguously that the message was from intelligent beings in space, it is perfectly possible to imagine a vast amount of additional information conveyed in ways that we can understand. For example, it is perfectly possible to transmit pictures. In fact, it's done by radio all the time. That's what your television set does. It is possible to send mathematics. It's very easy. I mean, suppose they set out the numbers-
Now, I would like you to just think about contrasting this open-minded, experimental approach, which consists of some plausibility arguments that no one takes too seriously, with the more traditional approach to intelligent life in space: the one in which there are no experiments, in which there is no withholding of opinion until the evidence is in, in which we are asked merely to take it on faith. The contrast is, in my opinion, very stark. There is quite a different approach in method. And I remind you about how powerfully we were fooled by the Martian canal situation, where passions and emotions were heavily engaged.
What do they look like? There is a standard Hollywood convention that extraterrestrials look just like us. Well, maybe they have pointy ears or antennae or green skin, but those are minor cosmetic variations. Extraterrestrials and humans are fundamentally the same. Why should that be? Look at the long sequence of stochastic random events that led to our evolution. I mentioned the extinction of the dinosaurs. That's one. Take another: We have ten fingers. And that's why we use base-ten arithmetic. Nothing special about one, two, three, four, five, six, seven, eight, nine, and then one-zero, except we count on our fingers. Why do we have ten fingers? Because we evolved from a Devonian fish that had ten phalanges in its fins. If we evolved from a Devonian fish that had twelve phalanges, then we'd all be doing base-twelve arithmetic, and base-ten arithmetic would be considered only by mathematicians.
This is true at every level, including biochemical levels, to such an extent that I think it is fair to say-never mind some other planet-if you started the Earth out again and let just these random factors operate, such as when a cosmic ray would strike a chromosome, producing a mutation in the hereditary material, you might wind up with intelligent beings after some thousands of millions of years. You might wind up with creatures of high ethical and artistic or theological accomplishment, But they would not look anything like human beings. We are the products of a unique evolutionary sequence. Unique doesn't mean better; it just means unique. Elsewhere, different environment, different necessity to adapt to changing conditions, a different sequence of random events, including random genetic events, and we should not expect anything like a human being.
Now, what about religion? What about the idea that we are all made in God's image? Is that also a failure of the imagination? What do we mean when we say we are made in God's image? Do we, for example, imagine that God has nostrils and breathes? If so, what does He breathe? Air? Where is the air? Air with oxygen in it? No other planet in the solar system has oxygen except the Earth. Why restrict God to very few places? Why would He need nostrils? What about a navel? Would God have a navel? What about hair? What about a vermiform appendix? What about toes? Toes are clearly the result of our ancestors' life in the canopy of the high forest, swinging from branch to branch. Very good to have four limbs that can hold on to trees. We just happened to have the toes in this particular transitional moment. Big toe is good for balance; little toe is not good for very much at all. It's just an evolutionary accident. Vermiform appendix? Likewise good for nothing. It's just on its way out.
Arthur Clarke has said that Christian orthodoxy is too narrow and timid for what is likely to be found in the search for extraterrestrial intelligence. He has said that the doctrine of man made in the image of God is ticking like a time bomb at Christianity's base, set to explode if other intelligent creatures are discovered. I don't in the least agree. I think that the only sense that can be put on the phrase 'made in God's image' is that there is a sense of intellectual affinity between us and higher organisms, if such there be.
