In a recent discussion with a friend about Avi Loeb’s hypothesis that the object ‘Oumuamua displayed behaviours consistent with its being an artifact of nonhuman technology, namely a light sail, one problem with the consistency of his thesis struck me.
A root problem with Loeb’s thinking that I have noted at length here is the unproblematic spontaneity of the very idea of nonhuman, extraterrestrial technology of the kind Loeb proposes ‘Oumuamua might be. It’s precisely the way the idea seems unquestionable, even as a speculation, that I argue is a mark of its being ideological and calling for scrutiny. (Interested readers are encouraged to click on the ‘Avi Loeb’ tag to access previous posts on this topic).
However, aside from “merely” philosophical reflection if not critique of Loeb’s thesis, one might propose a problem with its internal consistency. If we suppose ‘Oumuamua to be a light sail, then it must have originated, however long ago, from a relatively advanced extraterrestrial civilization. If said civilization were sufficiently sophisticated to imagine, design, and manufacture a light sail, is it not likely the same civilization had at the same time if not earlier developed a form of artificial communication that employed some frequency of the electromagnetic spectrum, e.g., radio? If this same civilization were to possess some such communications technology, then it seems arguable that signals from this civilization would have reached earth long in advance of a light sail, given their relative velocities. In the same way, long before any light sail or subluminal spacecraft from earth will reach another solar system, all the EM emissions from our communications technology will have reached that solar system long in advance. Therefore, subject to a whole raft of assumptions, admittedly, imagining a light sail arriving in our solar system suggests that signals, intentional or otherwise, from the home civilization of said light sail will have alerted us to that civilization’s existence long in advance of the arrival of their spacecraft.
Just a thought, and one I doubt is original to me. (Nor should the implications of this argument for the Extraterrestrial Hypothesis for the origin of UFOs/UAP be underestimated…).
Skunkworks 
Wait, explain this a bit more. Wouldn’t it be possible for the light sail to reach us and for the civilization from which it hailed to have stopped transmitting long ago (nuclear war, ecocide, or the use of line-of-sight communications like lasers and masers?)
I guess it would depend on the relative velocities of the electromagnetic radiation and the light sail, but if the light sail took thousands of years to reach us (because it was traveling at non-relativistic velocities, or because it’s from the other side of the galaxy), the home world could have stopped transmitting (or effectively stopped transmitting, depending on their extant methods of electromagnetic communication).
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You raise a very good objection here. Surely, _another_ possibility, precisely the one you raise.
But, then, the thought experiment is premissed on the assumption that _there is only the one_ extraterrestrial civilization, namely, that which built and launched the light sail.
Here, the problem of _the very form_ of the argument is revealed: it becomes a kind of speculation (a kind of “hard” science fiction, at best) of the precritical kind (does the world have a beginning or not, etc.). We posit one seemingly not too out-there possibility (an exoarcheological artifact), which then entails equal or slightly less plausible possibilities (the originating civilization, like ours, must have used some EM communication, too), which then prompts a no less reasonable but equally speculative rebuttal (your own), which, in turn prompts another response (but, if there is one such ET civilization, then it seems as likely there are others), and so on. And never do we agree on how many angels can dance on the head of the pin.
My note was hurriedly composed. I imagine in the back of my mind was the idea that, for speculations of this kind, where there is one ET civilization, there are many, which in a much more compelling way raises the question of the Great Silence (space should be a-chatter with signals,. but it isn’t).
This problem is all the more urgent for those persuaded that at least some of the unexplained sightings in the recent UAP Assessment are ET spaceships.
Thank, again, for the very much appreciated, cogent comment!
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