Ever absent, ever near.
Francis Kazinczy, Separation
In 1987, Martyn Fogg proposed the interdict scenario — an expanded form of the zoo scenario that provides reasons why all life-bearing planets, not just Earth, are off limits.61
Fogg first presented the results of a simple model of the origin, expansion and interaction of early Galactic civilizations. Like many authors before him he found that, using seemingly plausible values for model parameters, the Galaxy fills relatively quickly with intelligent species. Depending upon the parameters, either a few species dominate with large "empires" or there are many different smaller "empires." The conclusion of Fogg's model is that, whatever the value of the parameters, ETcs would colonize the Galaxy even before our Solar System forms.
Fogg argues that once the colonization phase is over and nearly every star supports intelligent life-forms, the Galaxy enters a new "steady-state" era. The expansionist urge withers, and the problems of aggression, terri-toriality and population growth are solved. The distribution of intelligence becomes increasingly well-mixed and homogeneous, and the steady-state era becomes an age of communication. According to the model, we are billions of years into this (wonderful sounding) era.
If Fogg's scenario is true, then Earth is located within a sphere of influence of one or more advanced ETCs. So why have they not taken over? He argues that, in a steady-state era, knowledge will be the most valuable resource. Advanced ETCs would have a reason to leave a life-bearing planet well alone, if only because the planet will provide a non-renewable source of information. And the sacrifice of lebensraum need not be great. As Asi-mov pointed out,62 ETCs might move beyond the need for planet-dwelling. If ETCs can travel between the stars in space arks, then they need not visit Sun-like stars; any star will do, and bright O-type stars might be best. Such space arks might therefore, on principle, avoid Sun-like stars with habitable planets. Fogg suggests the number of stars that ETCs must avoid may be small: he gives a figure of 0.6% for the fraction of stars possessing a life-bearing planet. (This figure is, of course, debatable.) Leaving a small number of systems untouched is a small price to pay for the information content their life-bearing planets will eventually possess.
In the steady-state era, then, an era in which ETCs communicate with each other and common approaches are agreed upon, the "Galactic Club" agrees not to interfere with already populated planets. In the words of Newman and Sagan,63 a "Codex Galactica" is established. Fogg's suggestion is that the Solar System was placed under interdict when, billions of years ago, an ETC visited the Earth and discovered primitive organisms. Since then, organisms on Earth have lived in a zoo — studied for the complex patterns of information they generate.
To my mind, some of the premises underlying the interdict scenario are unconvincing. To take just one, I believe that the cultural homogeneity that Fogg suggests is unlikely to come to pass. I find it implausible that truly alien intelligences, if they exist, can communicate so efficiently that they reach "an enhanced level of understanding [and] mutual agreement." The problems in establishing a transgalactic communication system go way beyond mere translation difficulties. For example, the differential rotation of the Galaxy causes a star like the Sun to move relative to other stars. Fifty million years ago, Earth may have been in a region of the Galaxy in which the zoo keepers were punctilious; right now, though, we may be entering a region where the zoo keepers have evolved and decided to take some time off. If they did that, who else would know? And what could the other members of the Galactic Club do to stop it? We live in a Universe in which there is a speed limit for information flow, and it makes Galactic cultural homogeneity extremely difficult to achieve. McDonald's may have conquered the world, but it will not conquer the Galaxy.
figure 19 A galaxy like this one is typically 100,000 light years or more in diameter. The interdict scenario requires a "Galactic Club" to be able to enforce its rules and traditions from one end of the galaxy to the other. In a relativistic Universe, this is extremely difficult to achieve.
So even without questioning the detailed parameters and assumptions underpinning Fogg's computer model, the conclusions are open to debate. Putting those reservations to one side, the interdict scenario suffers from some of the same criticisms as does the original zoo scenario. There seems to be no way of discovering whether we are under interdict (until, perhaps, we advance enough as a species to be elected as members of the Galactic
Club). So there are no testable predictions. The scenario also supposes that advanced ETCs, at all stages in their own evolution, can hide their activities from us. Well, maybe they can. But if the Galaxy really is teeming with ancient ETCs, as is suggested, would we not see the occasional grand astroengineered structure or overhear the occasional piece of interstellar gossip? Putting a planet under interdict is one thing; hiding all evidence of their existence from us is something else. Finally, as discussed above, even if deep communication were established in the steady-state era of the Galaxy, would a uniformity of motive regarding life-bearing planets really arise? The existence of just one advanced ETC that does not share the values discussed above could be enough to invalidate the scenario.
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