FROM EDN EUROPE: Is anybody there?
Staff -- EDN, January 6, 2005
A group of information theory researchers from the University of Michigan and the Max Planck Institute in Leipzig may have dealt a blow to searchers for signals from extra-terrestrial civilisations. The best-known of these efforts is probably SETI (Search for Extra-Terrestrial Intelligence); readers may even have hosted some of its signal processing algorithms on their own PCs, as part of its distributed processing program. (That web-based program is an interesting exercise in its own right, currently running as the equivalent of a machine of over 60 TeraFLOPS; see http://setiathome.ssl.berkeley.edu.) However, the new research calls into question whether, should we receive such a signal, we would recognize it for what it is (Reference 1). The paper extends Claude Shannon's classic information theory; according to Shannon, information coded at maximum efficiency is indistinguishable from random noise if you don't know the coding scheme. The new paper extends this principle and shows that the same result is true for RF transmissions; with no knowledge of the modulation or coding that is being used, a maximally-efficient signal will look just like thermal noise. So, if a radio astronomer does intercept a message from an efficiently-coded source, it will look just like a faint star. If ET is out there, our best hope may be that he skipped the class on Shannon's theories.
Reference
1. "The Physical Limits of Communication, or Why any sufficiently advanced technology is indistinguishable from noise," American Journal of Physics, November 2004.
