Signals in Analog
That's the the question David Galbraith asks when wondering why the SETI phenomenon has so far come up empty. It refers to the use of Reverse Turing Tests or "captchas" as they're more widely known.
What's a captcha?
The Reverse Turing test or 'captcha', usually contains a noise filled image of a password with warped fonts is used to filter humans from computers, to stop spam. In this instance a very simple digital message is encoded in a very analog way.Everyone who has ever utilized a free email or payment service on the Internet has experienced these things.
Without dwelling on likely Alien Propensities - hekk! he never even mentions the word "Aliens"- Galbraith makes an interesting, if somewhat arcane from my POV**, argument that that the current SETI program is looking in the wrong way for singles. It wants them to be clean, unencumbered by static noise and natural disruptions. It is quite possible that an advanced enough civilization would actual utilize this natural chaos as part of the medium of its messages.
Its a cool idea.
** Especially since I thought it was understood as Fact that our brains ARE an analog mechanism... Well, there's always more to learn eh...