What Kind of ETs Should We (Not) Care About?

Alfred Kracher
Iowa State University, USA

Receiving a signal from an alien intelligence would be great. Understanding it would no doubt be better. Best of all would be to have a meaningful conversation. Leaving aside questions of hard science, such as the formidable obstacles to two-way communication, is “meaningful” a realistic expectation? Is it even possible? SETI/CETI universally assumes the universality of mathematics, or a strictly formal symbol system, as a basis of communication. But this is only meaningful in a very restricted way. We cannot say “hello, how are you?” in mathematics without assuming that the recipient can independently infer meaning by some pre-existing analogy with the sender. Truly understanding each other is a problem of the relationship between formal and natural languages, which has occupied analytic philosophy and linguistics for over a century and is still controversial.

Information becomes meaningful in relation to a way of life. To the extent that we can apprehend the way of life of the conversation partner, we can understand messages. In interstellar communication this might be possible if it turns out that the evolution of extraterrestrial life forms is highly convergent with our own. There is no agreement among exobiologists that this is the case, but we might get lucky. Nor is it clear that physical convergence will be accompanied by convergence of the higher mental faculties. On this subject scientific assumptions seem to me to be highly biased by historical philosophy whose limiting influence is ignored or denied. There is as yet no way, even among terrestrial organisms, to evaluate mental divergence/convergence in the same way as in the evolution of organs and physical features.

It has also been suggested that the mental giants of the Milky Way are probably artificially intelligent machines which will not be limited locally to what we think of as habitable zones. It would be interesting to find evidence of them if they exist, but then what? If they have themselves emacipated and evolved away from their makers, they will have nothing in common with organic life forms, human or extraterrestrial. There is no chance of mutual understanding, not even a machine process that could justifiably be called that.

For these reasons SETI/CETI will likely be most productive by concentrating on environments that are as Earthlike (and of course as close) as possible. Similar environments increase the probability of evolutionary convergence and therefore forms of life that could just, if we (and presumably they) are very lucky, work toward a meaningful conversation.


Alfred Kracher (Ph.D. Chemistry, University of Vienna) is a retired Staff Scientist at Ames Laboratory, Iowa State University. He studied the chemistry of meteorites and lunar rocks, first at the Museum of Natural History in his native Vienna, later at UCLA, the University of New Mexico, and the Arkansas Center for Space and Planetary Sciences at the University of Arkansas. For his relevant publications see the section on space science and extraterrestrial life at https://independent.academia.edu/AlfredKracher. A recent presentation at the SETI Institute can be found at https://www.youtube.com/playlist?list=PLw6IJozmaWbSY1dIpKUOgqjfqXgB6cC76.