Any Sufficiently Advanced Civilization Is Indistinguishable From Nature

I first came across this idea, I think, at Charlie Stross' blog some weeks ago.  I only chewed on it a bit, because I think I was still zoned out after finishing GUN MACHINE.  But it's just popped up in my feeds again, and this is the takeaway:

(Karl) Schroeder explains the Fermi Paradox – the apparent contradiction between the likelihood that extraterrestrial civilizations exist and the lack of evidence for them – by speculating that we have not yet encountered our cosmic neighbors because they are indistinguishable from their native ecology.

Which is a fascinating thought experiment, and gives a marvellously wiggy megascale corollary to Arthur C Clarke's famous dictum about any sufficiently advanced technology being indistinguishable from magic.

What I haven't seen dealt with yet in my skim-reading of the topic, and maybe it'll be there when I drill down, is this: the experiment seems only to work if we assume such societies generated no electromagnetic noise at all in their transition to that level of civilisation.  We have to conceive of a civilisation that had no period of electromagnetic broadcast in its lifetime, or else there would be ambient evidence and Fermi would seem to me to reinstate itself.  Which is a fascinating workout for the imagination.