The most common answers to Fermi's famous question "Where is everybody?" are some version of either "we're unique", or "something makes intelligent species short-lived on geological time-scales". This second category corresponds to Drake's Omega Factor and could be the result of self-destruction or predation by nearby interstellar replicators.
A far more plausible explanation for our failure to find anything so far is summed up as "They're out there, but we haven't been looking for long, and we don't know what to look for anyway." The good people of SETI have said that so far, all we can conclude that the sky is not littered with constantly-blaring high-power microwave transmitters. Such cautious phrasings are wise. And from such a specific statement as this, are we really able to generalize that we're the only nearby intelligence?
Assuming that intelligence and tool use progress at roughly similar rates in other species, consider the gap in cognition and tools in our own species just over the past 100,000 years. And what is the chance that a planet-bound intelligence would be synchronized even within an order of magnitude of that timeframe? Would H. erectus understand our attempts to communicate? Would we even recognize our own million-year descendants, much less understand them? Now apply that to space-tuna, and you see the magnitude of the problem.
To say we haven't found anything so far, and therefore there are no non-human intelligences, seems foolish. We are barely a half-century into trying to answer this question, and it's not clear that we even know what to look for.
I reiterate that the best place to look for evidence of extraterrestrial replicators are the asteroids and the comets of our own solar system (my reasoning is here.) We should be looking for chemical traces of von Neumann biochemistry, not radio signals grandly announcing their presence. While I don't expect a thorough investigation of these bodies to be completed in my lifetime, I would be thrilled if it were. A lack of findings would cause me to dramatically lower my estimation for the chances of extra-terrestrial replicators.
Reading diary, #55
1 hour ago