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The Search for Extraterrestrial Intelligence (SETI) in the

Optical Spectrum


Monte Ross: First of all, I agree totally with Barney's comments. As long as the data rate is slow, it's going to take a long, long time. The first impact will dissipate very quickly. But if the data rate happens to be such that lots of information comes in quickly, where the information is something that really makes an important difference to us, then, after the initial die-down, something important can happen in a couple of years. But that is highly unlikely. I think that it will be a lower data rate and it will take a long integrated time for something significant to result from it.

Jim Lesh: I believe that what we are currently doing is looking for a needle in a very large haystack, and we know not whether there is a needle in the haystack at this point! If someone were to say "Yes, there is a needle in the haystack and it's in this portion of the haystack." or that "There are multiple needles in there, and these are some of the places where there is a higher concentration of needles.", then I think that there will be systems developed that will concentrate on those regions and the progress that will be made will be much faster. I do believe that it will be all over CNN for a while - it will die off - but I think that the national programs that support the scientific research will be stimulated substantially and there will be great increase in the rate of progress in finding those needles and understanding them.

Stuart Kingsley: May I comment? I want to surprise everybody and say that I agree with Barney, and my co-chair.

Barney Oliver: Well done! [laughter]

Neil Tennant: Someone mentioned you would have to know how close they were, and that raises the prospect that they may be visiting in person, whatever a person is. I think that is very important. But let's try to separate out two distinct aspects of the problem; the social and political aspects, and even the religious aspects, from what I would like to call the cognitive aspects, the sheer theoretical value of having a confirming instance; that there is an "X", where "X" is extraterrestrial intelligence, and has signaled us. Now, you are looking at the rational decision-making framework for devoting resources to a search, a positive result of which is confirmation of an existential claim that there are things of this kind. The negative result of which is that you do not know whether or not they exist or they might without your detecting them, on the other hand you might not.

Then you have the following problem: Before you engage in the search and before you even decide whether to undertake the search, you have on the grounds of other theoretical considerations like cosmology and evolutionary biology and so on, a subjective prior probability that you attach to the belief that there are things that are as yet an unsubstantiated, unexamined, undiscovered kind. Each one of us here could go through a Ramsey test to find out the degree of subjective belief in the claim that there is an extraterrestrial intelligence that might be able to communicate with us.

So you have this subjective prior probability. Now, take someone that is so convinced in the existence of extraterrestrial intelligence that the probability for them is one. Then actually discovering it, is a kind of a "Ho-hum, I told you so!" experience. So for them, the cognitive value of the discovery is more like zero.

Now take someone who is extremely skeptical, who has a prior probability of right down near zero, but then has overwhelming evidence in the form of discovery, that they do after all exist. For that person, the cognitive value of the discovery is up near one. So you have something like an inverse, and let's say for the sake of argument, linear relationship between prior subjective probability and the cognitive value of the discovery, should you make it after devoting the resources to it.

Now you have to decide how to maximize the expected cognitive utility of the search. The expected cognitive utility of the search will be the proportionality constant, v, the top cognitive value you can get, times p times one minus p, i.e., vp(1-p). That peaks for this inverse linear relationship at the subjective probability of 0.5 at the value of v/4. This is a straightforward piece of rational decision theory. The conclusion is inescapable that if you want to maximize the expected cognitive utility of a discovery before you undertake the search, you should be ever-so-cool about the possible outcome. You should have a completely open mind. And that's why I think it's headquartered in California! [laughter]

Now, if you put a different function in here - something like the arc of a circle, either convex or concave, or something sinusoidal, you get the same qualitative argument, except the value changes from 0.5 to something else in its neighborhood. But you still get this thing I call the "paradox of pure curiosity" - that there is some particular subjective prior probability which it is best for you to have in order to be able to maximize the expected cognitive utility of undertaking a search in the first place.

Barney Oliver: Is that any different than saying that the information received on the average will be maximum if there is a maximum of uncertainty to begin with?

Neil Tennant: I beg your pardon. [laughter]

Barney Oliver: If the uncertainty to begin with is a maximum, the value is 0.5, then you get the maximum information from confirming the discovery.

Neil Tennant: I guess it is all the same.

Charles Townes: I see one more hand up.


Copyright , 1993, SPIE

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