May 16, 2012
When invoking the Great Filter as an explanation for the Great Silence, we have yet to determine the exact nature of the filter. It's conceivable, though unlikely, that it resides in our past (fingers are crossed that this is the case). If so, the rise of prokaryotes and eukaryotes is probably what we're looking for.
But, if the filter resides in our future, the question needs to be asked, What is it exactly that prevents civilizations from embarking on interstellar colonization?
One of the stronger, though more disturbing suggestions, is that all civilizations destroy themselves before they can send out a wave of self-replicating colonization probes. For the sake of this particular argument, let's assume that doom is in fact the Great Filter. If this is the case, what could it be, and when would it happen?
It's probably not environmental devastation, as that's a weak force for something that's supposed to be existentially catastrophic, nor does it seem universal as far as extraterrestrial civilizations are concerned. It's more reasonable to suggest, therefore, that something in our technological arsenal will destroy us. It's clearly not nuclear weapons, as we've figured out a way to live alongside their presence; there's even talk of disarmament. So, it has to be something we come up with in our future. And whatever that technology is, it has to be completely uncontainable and catastrophic.
Only two things come to mind: molecular nanotechnology and machine superintelligence.
Given that doom has to come before the launch of self-replicating probes, this indicates that we have to experience doom prior to the invention of diamondoid data storage and nanocomputing along with the requisite robotics and AI capacities; these are the ingredients to von Neumann probes. It also means doom before, or at the point of, the advent of strong artificial general intelligence (because an SAI could develop probe-enabling technologies). This would suggest that either (1) the onset of machine superintelligence is somehow causing the filter or (2) the precursors to probe-enabling nanotechnology are fatally catastrophic in all instances (e.g. weaponized molecular nanotechnology).
If this is the case, then I would expect doom no earlier than 25 years from now, but no later than 50-75 years from now.
There's also the possibility, of course, of a wildcard technology (either through convergence or something we haven't considered yet).
Again, I'm not suggesting that doom is certain — there are other non-doom explanation for the Fermi Paradox. I'm just venturing down this particular line of inquiry.