At 10:18 AM 2/20/2012, Jed Rothwell wrote:
Advanced civilizations may not use RF communications. Or the signal may be so compressed it looks like noise. However, they will recognize it when they detect it. If they use radio telescopes they will probably realize they have intercepted a signal from a civilization, and not a natural signal.
Jef Poskanzer pointed out a few years ago that spread-spectrum encrypted radio traffic would be indistinguishable from white noise. This was when a broad-spectrum microwave stellar source was found, and there wasn't a physical explanation for it. (The astronomer didn't like his explanation).
