I was reading Charles Stross’ novelette A Colder War recently and was struck by its mention of a “Great Filter” in reference to the seeming lack of intelligent, technological life in the universe. A search for the term quickly showed that it arose from a discussion of the Fermi Paradox by Robin Hanson. I have a few problems with the arguments Hanson makes in the discussed essay.
The most obvious is that Earth may well have already been colonized by extraterrestrial life. Chemolithotrophic bacteria are thought to be terrestrial, but it’s been speculated that they exist elsewhere and may have originated somewhere other than our planet. Perhaps the kind of life that dominates the universe is so familiar to us that we don’t recognize it under our noses.
A somewhat more subtle issue is with the assertion that we’ve had great success understanding the universe without referring to complex processes of life. Well… sort of. Interestingly, Carl Sagan addresses this issue in fiction in his novel <u>Contact</u>, in which a conservation with an alien being indicates that some of the things we can see in the night sky are the beginning stages of a vast engineering project. We never noticed because we derived our ideas about how astronomical processes work from our observations – and thus those observations necessarily do not contradict our ideas.
I remember reading another author who suggested that we could observe distant galaxies and possibly determine whether it had advanced life by checking the number of supernovae in them against our ideas of their natural frequency – if there were far fewer, that galaxy contained advanced life (because it was stopping them) and if it had far more, it had contained advanced life (because it found a way to use stars as weapons).
The argument only holds if we make certain assumptions – clearly, that advanced life could and would affect the behavior of stars – but also that most galaxies are devoid of life. Since our grasp of the internal physics of stars is currently derived by what we can deduce by observing large numbers of them from a vast distance (in both space and time), if many galaxies contain organisms that alter the supernova rate our understanding of what’s ‘natural’ will be incorrect.
It’s not obvious to me that moderately advanced life would have effects that we could detect at a distance, given our scientific and technological limitations. But I strongly suspect that sufficiently advanced life could be leaving its signature all over the place without our awareness, because it determined what we consider to be natural. Can a colony of bacteria really distinguish between a forest and a strip mall?