SETI is the Search for Extraterrestrial Intelligence. Much of it might be better re-titled, "search for stupidity" because the most obvious ways aliens might try to detect us, rely on the stupidity of humanity. If you want to transmit information optimally your signal will bear a great resemblance to "thermal noise" because that is the signal with the greatest entropy for a given power level. However, being as humanity is stupid, it creates a lot of signals that are not at all like that. In particular, high-def television (USA) is incredibly stupidly done, plus involves a high amount of periodicity at the screen and line refresh rates. Similar remarks could be made about, e.g. radar systems. TV and radio commercials that keep being re-broadcast could be spotted as a statistically amazing exact repeat of the same stuff. Of course, an alien would be detecting that stuff polluted by a huge amount of noise, so it would not be an exact repeat. But using FFTs one could detect statistically amazing periodic components of signals, and also do autocorrelations to detect statistically amazing high correlations between F(t) and F(t+delay). This all is computationally cheap (NlogN time). If however you were to examine some time-window and compare it with a different time-window to detect a repeat that way, you could get a lot more sensitivity to that repeat than from any FFT-based autocorrelation, but the compute cost would be much greater to try many possibilities. So, far as I can tell, what I just said summarizes a large set of SETI efforts. A paper on this topic: http://setiathome.berkeley.edu/sah_papers/status_of_ucb_seti_efforts_2011.pd... If anybody were intentionally trying to communicate with us, a good way seems to be using short powerful optical laser pulses. Optical is far superior to radio because it can be directed more precisely. Laser pulses from the largest lasers available today could easily outshine our sun during the short (nanosecond scale) pulse, as viewed from far away in the shining direction, and if we only observe in a small band near the laser frequency, then the outshining of the sun can be made an enormous factor. A paper on that: http://seti.harvard.edu/oseti/oseti_apj_preprint.pdf which was published as Howard, Andrew W.; Horowitz, Paul; Wilkinson, David T.; Coldwell, Charles M.; Groth, Edward J.; Jarosik, Norm; Latham, David W.; Stefanik, Robert P.; Willman, Alexander J., Jr.; Wolff, Jonathan; Zajac, Joseph M.: Search for Nanosecond Optical Pulses from Nearby Solar-Type Stars, Astrophysical Journal 613,2 (Sept 2004) 1270-1284. The Berkeley paper includes "figure 1" showing 112 locations of about 330 unexplained statistical outliers their "astropulse" program detected, on the sky. (Seeks 1 microsec to 1 millisec long radio pulses and tries to discard ones from terrestrial sources.) The surprising(?) thing: these locations are claimed to be concentrated near the Galactic Plane, in a way that is statistically significant. If this concentration cannot be explained as terrestrially caused, then I guess that "proves" that whatever triggers their "I found something" detector, is coming mainly from our galaxy. And if, furthermore, natural sources could not have produced such pulses, they would have to be artificial. The Harvard-Princeton optical pulse paper found only one mysterious optical pulse event after using several telescopes each with about 1 meter diameter totaling about 2400 hours observing time observing 13000 nearby stars. Just one pulse was simultaneously detected by more than 1 telescope. This event came from the K class late dwarf called "HIP 107395" and occurred on 17 sept 2003. Unfortunately their hyperaccurate atomic clock wasn't working at this time, hence they were unable to confirm their two telescopes got the pulse within e.g. the same microsecond; they only had millisecond accuracy. Hence this detection is not a statistically sure thing, albeit it still seems suspicious -- why the hell should such a star be emitting a microsecond long (or less) optical pulse (or two such, separated by a millisecond or less)? -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)