THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE

Posted by admin_akashic on Jun 27th, 2022 in Space

slow down their metabolism; future developments in biology which could make it possible to freeze and thaw out warm-blooded animals. Hopefully they would take self-functioning instruments to do this with them as there would not be anyone waiting at the end of the journey to thaw them out. Or, as Hart speculates, extraterrestrials might not be warm-blooded, thus circumventing this problem. The length of time required for the journey might not be a problem for extraterrestrials who may have life-spans lasting many thousands of years and not regard a 200-year journey as a dreary waste of one’s life. Deep into the realm of speculation, Hart also considers frozen zygotes sent out in spaceships piloted by robots, or the use of techniques of time dilation. A journey lasting many generations could be mounted, as long as comfort and a well-organized social structure was part of the conception. The energy requirements pose few problems for Hart, who envisages nuclear-powered rockets scooping up oxygen as they speed through the galaxy.

Hart also rejects sociological explanations of the silence, which maintains that they choose not to come because of a lack of interest, motivation, organization, or because they suffer from a tendency to self-destruct. The weakness in these explanations, says Hart, is that they fail to consider the fact that civilizations can and do change. These explanations, he says, may only hold for one civilization at any one time. To cite them as an explanation of silence would require showing why they hold ‘for every race of extraterrestrials – regardless of its biological, physiological, social or political structure – and at every stage in their history after they achieve the ability to engage in space travel’ (Hart, 1975: 132). Hart dismisses as a non-testable hypothesis the argument that advanced technological societies are likely to self-destruct. There is no evidence of any doing so, he says, and the only one we can observe has, so far, not self-destructed.

SETI advocates, it would seem, cannot have it both ways. If, as SETI expo-nents argue, life on Earth is typical, then they are obliged to acknowledge the possibility that some, if not all, extraterrestrial civilization will have colonizing tendencies like ours. Of course they might respond that we are typical, and that just as our colonizing tendencies evaporate with the awareness of the massive costs involved and the immorality of such conquests, so it would be with extraterrestrials.

Hart’s third category of explanations for the absence of extraterrestrials is classified as ‘temporal explanations’. These explanations appeal to suggestions that they have not yet had enough time to reach us. To assess the plausibility of this explanation one needs to know how long it could take a civilization to reach us once it has embarked on a programme of space exploration. Hart considers expeditions from Earth to the nearest one hundred stars as a typical example. These are all twenty light years away from our Sun. Colonies might be established near them from which further voyages could be launched. Without any pause between trips Hart estimates that the galaxy would be traversed within 650,000 years (ibid.: 133). If we allow for a period between each wave of expansion of about the length of time it takes for each voyage, this would double the total

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number of years. But this would still mean that an advanced civilization should have reached us by now, unless they began their colonization less than 2 million years ago, says Hart.

The fourth and final explanation of absence rejected by Hart is that they have visited us but that we are not aware of it. There is no evidence that they are here now so, presumably, they were here some time ago. But if it is suggested that they came within the last 5,000 years, says Hart, a sociological theory is required to explain why no other extraterrestrials have visited since and why they do not remain here. Moreover, he adds, if it is suggested that they came and chose not to colonize, then a sociological theory is required to show why every civilization which could have colonized chose not to. Appeals to arguments which assert that they might not wish to colonize grow weaker, argues Hart (1980), as estimates for N increase. Given a tendency for SETI optimists to inflate N, then the chance of colonizing societies emerging has to be greater. In this way SETI’s own arguments in favour of a galaxy teeming with ETI are rendered self-defeating.

Hart’s rebuttal of explanations of absence is hard to sustain. Granted it only requires one colonizing advanced civilization to cover the galaxy within two or so million years, but there is no reason to assume that even one civilization out of billions will emulate the behaviour exhibited by some human societies over the past few thousand years of recent history. The possible fact that no benefit could outweigh the costs of large-scale colonization could apply to billions of technological civilizations. Moreover, there may be an infinite number of sociological reasons, or a combination of all four of the explanations of absence, which could account for the failure to colonize.

Despite Hart’s assertion that we have no evidence of them, it is possible that the galaxy is teeming with forms of advanced extraterrestrial life, who are so advanced that we are unaware of them, yet being much more advanced, they would have no interest in revealing themselves to us.

Hart’s four arguments against explanations of absence and his solipsistic conclusions rest on appeals to many unknown and as yet undiscovered scientific techniques, and assumptions that practices which have existed for a small part of human history are likely to be repeated universally.

Tipler’s self-replicating colonizing probes

John von Neumann conceived of a mathematical proof that self-replicating machines could exist. All that is required is the appropriate technology. An extension of von Neumann’s reasoning would be to conceive of a programme whereby robot probes could be set into motion with the purpose of colonizing the galaxy. It would take one – out of the possible millions – of civilizations to colonize the galaxy, given enough time. Self-replicating probes, like rabbits spreading across Australia, would eventually reach our corner of the galaxy. David Brin (1990: 160) cites calculations by Eric Jones of Los Alamos labora-tories which suggest that an expanding sphere of settlements could fill up the

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