Classical SETI 3. The SETI Paradigm

The fundamental assumptions concerning the conditions for life in the universe, combined with certain well-established physical and engineering principles, create the paradigm, or point of view, which shapes the SETI program. Its major features are as follows:

1. Extraterrestrial intelligent (ETI) societies are not going to travel here physically. The only way we can learn of their existence is to observe signals transmitted from their home location.

 
2. Although we don't know how many ETI societies there are, at least a subset of any that exist may establish electromagnetic beacons, optimized for detection by a society such as ours. Such beacons, if they exist, would be easier for us to detect than any other feature or activity of ETI societies (all other factors, such as distance from us, being equal), because they are constructed so as to facilitate detection.

 
3. Beacons (if they exist) are distributed throughout space in the same way that the stars that engendered them are. If they are so common that most stars have one or more of them in their vicinity, then we should search the area around the stars nearest to us. If they are less common than that, we should search all directions equally, since at a scale of tens of light years in our galactic neighborhood, stars are uniformly distributed. If they are still less common, we should search the more distant reaches of our spiral arm in the Milky Way, etc. But since we don't know how common they are, a good search strategy would incorporate both a selected star search and an all-sky search.

 
4. Although electromagnetic energy can exist over an infinite spectrum, choices for listening are more limited: at lower frequencies our atmosphere is opaque; at higher frequencies, scattering by cosmic dust and high levels of background radiation interfere with the reception of weak signals. ETI civilizations can be expected to understand these factors — presumably including the transmission spectrum of our particular atmosphere — and confine their beacon transmitters either to the clear and quiet frequency zone — the so-called "microwave window" — or, according to a new school of SETI, to optical frequencies.¹²

 
5. Any given set of transmitting and receiving characteristics determines a maximum range over which signals can be received. Therefore, a given receiving system on Earth can detect transmitted signals originating from within a rough sphere whose radius is that maximum range. The number of possible transmitting sites in any given thin spherical shell within that maximum-distance sphere varies as the square of the radius of that shell.

   This means that the preponderance of those sites will be near the maximum receiving distance and their signals will be near the limit of detectability.

Here is another quote from that NASA workshop on the social implications of detecting ETI:

"Might an old and highly advanced extrasolar civilization have discovered ways [to send an object across interstellar distances]? We don't know. If we thought so, and if we had reason to believe that they had explored the solar system, we might search for physical artifacts left by their explorations. Such a search might involve examination of the Earth's geological strata for a buried 'message capsule', or a comparable search of the planets, or efforts to detect a relic orbiting vehicle in our solar system. However, the certainty that interstellar travel is exorbitantly costly in time and energy (if not flatly impossible) has persuaded most SETI researchers that a search for artifacts is not the best option." (Klein, 1994)

But what if physical artifacts should turn up anyway? Would that be sufficient to justify a changed approach to SETI? A review of the SETI literature reveals precisely the opposite. The record shows clearly that evidence of such suspected artifacts has not been followed-up, but has instead been linked, a priori, with the most problematic aspects of the UFO field, pseudoscience, and the tabloid press. It appears, then, that SETI researchers would rather not hear about physical artifacts or traces of ETI in the solar system.

Reluctance to admit evidence of ETI extends even to the modality of the SETI paradigm itself: electromagnetic signalling. As we will show, it is not only SETI but the larger astronomical community that fails to acknowledge readily-available evidence - although one would expect SETI practitioners to be more disposed than their fellow astronomers to examine the evidence. Perhaps the problem lies in the inability of modern society itself to accept the challenge that is now being presented to it.
 

In the remainder of this essay I will explain a bit more about how SETI works, providing a basis for understanding it at least to the degree needed for examining the SETI program's effectiveness. I will show how SETI searches are blind to the evidence that has already been received by radio astronomers. I then outline a new and more liberal set of fundamental assumptions, giving rise to the Open SETI paradigm - the paradigm for an entirely different search.