The Fermi paradox vs the “Undetectability Conjecture,”
“Evolutionary selection, acting on a cosmic scale, tends to extinguish species which conspicuously advertise themselves and their habitats,” according to Adrian Kent, Centre for Quantum Computation, University of Cambridge.
The Fermi paradox is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations. As Enrico Fermi asked if the Universe is conducive to intelligent life, “Where is everybody?”
An answer proposed by Adrian Kent of the University of Cambridge and Perimeter Institute, is that extraterrestial life sufficiently advanced to be capable of interstellar travel or communication must be rare, since otherwise we would have seen evidence of it by now. This in turn is sometimes taken as indirect evidence for the improbability of life evolving at all in our universe.
“Intelligent species might reasonably worry about the possible dangers of self-advertisement and hence incline towards discretion” -- the “Undetectability Conjecture,” put forth by Beatriz Gato-Rivera, a theoretical physicist at the Instituto de Fisica Fundamental (previously Instituto de Matematicas y Fisica Fundamental) of the CSIC (Spanish Scientific Research Council) in Madrid.
According to Gato-Rivera, we may find ourselves in a universe in which there exist intelligent technological civilizations but they have chosen to be undetectable, camouflaging themselves mainly for security reasons (because advanced civilizations could also be aggressive).
“It often seems, Kent concludes, "to be implicitly assumed, and sometimes is explicitly argued, that colonising or otherwise exploiting the resources of other planets and other solar systems will solve our problems when the Earth’s resources can no longer sustain our consumption. It might perhaps be worth contemplating more seriously the possibility that there may be limits to the territory we can safely colonise and to the resources we can safely exploit, and to consider whether and how it might be possible to evolve towards a way of living that can be sustained (almost) indefinitely on the resources of (say) our solar system alone.”
http://www.dailygalaxy.com/my_weblog/2012/09/cosmic-camouflage-advanced-et-civilizations-may-be-undetectable.html
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> he is suggesting that some species would not share it either - and therefore decide to hide, just in case aggressive interstellar species do exist.
Since we haven't heard a "peep" from any other species, he must be saying ALL species that become capable of radio, not just some.
Further, the idea of self-replicating robots, exploring the galaxy for thousands if not millions of years, doesn't add any risk to "shy" species. Complete anonymity about where the robots came from would be easy to design into them. But we don't see these, do we? Unless UFOs are them ... 
> As described in the OP, the Fermi Paradox is not something in which you can 'believe'.
I agree with his thinking, that created his Paradox. That we aren't hearing from aliens for a reason. Should've added that earlier, although I thought it was obvious.
> If you want the robot to send back some information, then it will be traceable - you take the robot apart, and work out where it would send information to.
No, you have it send radio signals back in many directions - which it would have to anyway since you would have no idea if it was upside down or whatever when it sent its signals.
> Yes, I suppose he is saying that all technological species will hide fairly quickly once they become visible.
So your theory means that 1 second after a species invents radio, they hastily shut it down? 
If you shut down radio emissions with a century or two, you're not taking up much time compared to the age of the galaxy, or the time it takes to travel around (if the speed of light really is limiting, which I assume it is).
Any self-respecting robot (and I think a self-replicating one would also be self-respecting 
) could use stars to orient itself so it would know which direction home is. Yes, I suppose you could broadcast in every direction (though it offends my sense of efficiency), but, if I was worried about aggressive species, I think I'd worry they'd be able to trace the route of a robot back, somehow.
> If you shut down radio emissions with a century or two, you're not taking up much time compared to the age of the galaxy,
Shutting down radio emissions isn't as easy as you think. Many physical processes, as well as electronic circuits, give off radio signals even if they're not designed to. You'd also have to shut down any space program of your own, as it communicating with your space vehicles requires radio (or a very long cord - which gives off its own radiation). Power generation. Essentially, you'd have to stop technology's progress nearly completely at some point, as the more complex and interconnected your planet is, the more radio signals it generates, albeit unintentionally.
> if I was worried about aggressive species, I think I'd worry they'd be able to trace the route of a robot back, somehow.
Just have the robot take a random path. Better yet, have your self-replicating robot build their next generation on a deserted asteroid or planet that had the requisite materials on it, far from the home planet. Then "tracing it back" does no good.
