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The Search for Extraterrestrial Intelligence (SETI) in the

Optical Spectrum


Clive Goodall (Floor): Could I comment?

Charles Townes: Yes, briefly.

Clive Goodall (Floor): I've had this argument explained to me the other day, actually Neil, by Don Hubin. Something occurred to me in the explanation of the probabilities. He gave the same explanation that you have just given. The expected cognitive utility is going to be different for the searchers (the SETI experts) than for the lay public at large who know nothing about SETI. Because of the fact that so many people outside the field of SETI are so ignorant of what the reality of the science is, and are so reluctant to treat or regard SETI as serious science, they are going to be resistant to accepting the idea that ETIs might be out there. Therefore no matter what the utility will be for the searchers, whether at the skeptical end or the less skeptical end of the scale, the expected cognitive utility is going to be very great for the lay people.

Neil Tennant: Could I say something quickly - a quick reply to that? It seems that there is something which is almost like a pragmatic paradox. In the propaganda efforts of the SETI community, I have been to presentations - I was impressed by one by John Billingham - where a lot of cosmological and evolutionary biological facts were presented for the benefit of a lay but educated audience. It was designed, it seemed to me rhetorically, massively to increase on the part of the audience the subjective prior probability that they might be prepared to attach to the claim that there exists extraterrestrial intelligence.

In other words, they are taking you too far to the right of this hump, thereby lessening the expected cognitive gains. It seems to me rhetorically that if you are being perfectly rational, and expect the audience to be perfectly rational, you should try to argue them out of their skepticism only up to the midpoint of the spectrum of probabilities. [laughter]

Barney Oliver: We'd like to go a little further for reasons like talking to congressmen. [laughter]

Charles Townes: I'm going to take the privilege of saying a few things on this. I enjoy these philosophical arguments. However, what is not contained in that is the importance of the question itself. One could say "What's the probability of a ten-dollar bill lying under the table?". You would then say that for those people who doubt it is going to be for them an enormous finding, if it's there, I think it is relatively unimportant. I think it's the subject matter itself which makes it important. I would look at it as a kind of functional thing and I would agree with what Dr. Lesher said: "If it's found (in the first place I think that there are some reasons for believing that life is really quite rare, but if it is found) there will be an intense scientific effort..." - an enormous scientific effort. Everybody will jump on trying to see "Is it real and what can we find out from it?", and so on.

It will be a very intense scientific effort. Will it be any value to us? From the point of view of technology, probably not. But from the point of view of culture, and of thought; I think yes. In the long run, I think it will be very profound. It will certainly affect the scientific community and a lot of people, I believe in terms of the search, and as we search, presumably we will find out something.

If it turns out we have got something, but never find out anything, - that it will take 10,000 years or so before we can get there or they can get to us before anything else can happen, then it might be slow yet, almost immediately I suspect - the cultural changes would be there.

I suggest that rather than continuing this somewhat philosophical discussion, which we can do a little bit later, let's go ahead and have the final three members of our panel say what they would like to say. Then we can round this off more at our leisure.

Kent Cullers: I have enjoyed today's discussions. I have heard some very well put arguments and fascinating descriptions of systems. But I am now going to express an extreme view, which I had sense enough not to write down in my paper, to see what I can stir up here. I'm going to be an extremist and say that if I could do SETI and free space were truly free, I would go for long wavelengths to do it. The reason is that at long wavelengths the area of an isotropic antenna is bigger. Essentially, you could eventually get to wavelengths that are so long that your isotropic antenna would have lots of collecting area, you could look at all the directions you wanted, your doppler effects and other things that are percentages of frequency go away and the whole problem is simple. We have small difficulties with that, there is a real plasma in space. But essentially, these arguments have gone back and forth over the years - as to whether longer or shorter wavelengths are better. I've always been slightly predisposed to wavelengths that are long enough to be usable, but not so long that they are utterly noisy.

I've noticed often that in this discussion things have been phrased as if it were a controversy; as if somehow the people that were predisposed to the longer wavelengths were unaware that there could be cogent arguments that there could be high gain antennas for shorter wavelengths, and I don't think that is really true. On the other hand, I am not sure that I have heard today arguments to say that we must in fact, for some kind of compelling reason, go to short wavelengths or some particularly good one. I've heard lots of arguments that say that lasers will work across large distances, which clearly are true. I just wonder how just some of the strong advocates of shorter wavelengths feel about this kind of thinking. In other words, do you see strong, predisposing reasons to go for optical or near-optical wavelengths in searches? And I guess that would be my only comment on this, it's been a fun session.

Charles Townes: OK, we'll move on, and then we will come back.


Copyright , 1993, SPIE

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