Absent Aliens?

Just a quick thought…

The Anthropic Principle – from an intellectual point of view, it’s largely useless. It makes few genuine testable predictions – Fred Hoyle is about the only person I’ve heard of who managed to get something usable out of it. And not only is the Anthropic Principle a useless bit of psychological fluff, at its worst extreme it can actually lead to some very, very silly intellectual places. So, on the face of it, the Anthropic Principle seems really a bit pointless.


It occurs to me that it might, just might, conceivably tell us something about the possibility of intelligent extraterrestrial life. The argument is this – we as human beings are an intelligent species, and we exist. Therefore, the logical inference is that intelligent life is definitely possible, and a basic scientific principle is that if it can happen once, it can happen again, given the right conditions.

So, this means that the debate regarding ‘aliens’ shouldn’t be ‘can they exist?’. Rather, we should be asking questions about the likelihood – and thus the spatial and temporal distribution. (10,000 civilisations at any given time in a galaxy the size of ours? Or one every billion or so years on average?)

And the nice thing about questions like this is that it should be possible to put at least some upper bounds on these numbers, even with today’s technology. The argument would be, if we can reliably detect (say) radio wave signals out to X parsecs, and we don’t, then we can argue an immediate upper bound as ‘no more than one civilization, i.e. us’ per X^3 cubic parsecs.

Divide the volume of the galactic disk by that number, and you have your estimate.


5 Responses to “Absent Aliens?”

  1. The devil is in the assumptions though; in this case the assumption that the ‘aliens’ are using some form of communication we can’t pick up, or that we either can’t or don’t interpret into inteligible information in our attempts to find them.

    I know Star Trek science is silly, but subspace, which they utilise both in FTL travel and FTL communication, is an example where the means by which they communicate are so different we might not notice them broadcasting at all.

    • In a word, yes. All we’ve actually established above is possibility.

      Of course, the eternal difficulty in science is that we have to proceed on the assumption that our hypothesis is testable as it stands; if not then problems will arise.

  2. There is, mind you, another caveat. Ignoring the possibility of another civillisation using a form of communication we can’t detect — there’s always the possibility they may not be trying to communicate. They may not be capable. Their signals may be so weak we can’t detect them (for instance, most of Earth’s signals would be drowned out by noise from the Sun)…

    • …which is, indeed, quite definitely also true.

      However, it does bring us back to the point of testability. For all practical purposes, if something can’t be seen in any way, then it may as well not exist.

      • With out current level of technology, this is certainly true. Philosophically though, as you said, if intelligent life can happen once then it can happen again. My point was more that just because we haven’t explicitly detected it doesn’t mean it hasn’t already happened…

        This has been thought provoking. Thank you. 🙂

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