Let me start out by stating that I am convinced the universe is full of life. I am convinced we found it on Mars during the Viking missions in 1976, even if NASA still follows the official line based on a flawed negative from the GC/MS. More than that, I think that extraterrestrial life is not a rarity, but is in fact the norm for all worlds born of the Type-1 metals-rich stars where there is a fluid medium or gas for mixing and a source of energy to power chemical reactions. Most science today focuses on the search for water-bourne carbon-based life, but this is a very narrow view that excludes life based on silicon, or floating in methane seas. We won't know until we find it, and only our water-bourne carbon-based prejudices would rule out the possibility.
That being said, there is no question that the detection of intelligent life on other worlds would profoundly change the human experience. We would know for certain that humans are not alone in the universe, and I think that a sense of humility that we are not the universe's supreme creation might go a long way towards reducing some of the cultural insanity that goes along with such arrogant notions.
At present, the search for extraterrestrial intelligence focuses on giant radio telescopes searching the heavens for signals intentionally sent our way much as the Earth sent a message into space from the Arecibo in November 1974. But that message was only three minutes in length and directed at the Globular cluster M13. The odds of intelligent life listening in the direction of Earth at the precise frequency and precise time that three minute broadcast arrives is remote if said intelligent life has no other reason to be paying attention. After all, if that intelligent life lives in methane seas, they might conclude that the third planet from the star is obviously way too hot to support "life as we know it" and their time is better spent looking elsewhere, if indeed they are include to look. And indeed the transmission of the 1 megawatt message was actually a publicity stunt to demonstrate Arecibo's new and upgraded equipment.
More recently, and realizing that the odds of a deliberate message being direct at Earth were remote, newer and more sensitive radio telescopes are searching nearby planets for signs of radio "leakage", trying to detect an alien world's equivalent of MTV and "I Love Lucy". Maybe they will get lucky. But humans have been on this Earth for a half million years, building a civilization for 20,000 years. But only in the last 100 years has Earth been sending radio and TV signals out into space, and as the giant transmitters of yesterday are traded in on cable and satellite, the total energy of radio leaking into space is already in decline. As we move more into optical cable, the Earth way well go "dark" with regards to outside eavesdroppers on our communications frequencies. No doubt this will be true of alien technologies. The window at which vast amounts of radio communications flow into space is very, very narrow. SETI researchers are searching for planets with 1950s level radio technology.
Which is why I think the SETI people are searching for the wrong thing.
There is one aspect of human life that radiates a great deal of electronic noise, one that is not likely to go away any time soon.
The Earth produces and consumes terawatts of electrical power. Earth uses alternating current because alternating current transmits power over distance more efficiently. Alien civilizations will reach a stage of electrical development and because the laws of physics are universal will also use alternating current. Like Earth, they will not change the system once the core infrastructure has been built. Here in the US we still use the 60hz system George Westinghouse devised in the 1920s and nobody is seriously suggesting that it will be changed any time in the future. Anyone who plays with radio knows what a constant headache "AC Hum" is, saturating the lower bands, and harmonics.
And THAT, not radio and TV, is what we should be trying to detect out there in the universe as proof of intelligent life! Not their 50,000 watt radio stations, not their 1 megawatt message aimed at us for a scant three minutes, but the noise from terawatts of power generation and distribution pouring out from transmission lines strung across their world, humming at very low frequencies in the range of (to start) 10Hz to 100Hz.
Phase one is simply an array of non-steerable loop antennas phase-locked together for directionality listening to the sky and seeing if there is a low frequency signal that comes and goes over 24 hours; the same phenomenon that led Karl Jansky to discover radio astronomy in 1933. If such a signal is found, then a more advanced search system can and should be considered.
No, we will learn nothing from such a signal other than that a world exists with electrical power, but once located, we know where to focus attempts to intercept more sophisticated communications ought to be focused.
I decided to try a quick experiment and threw together the following setup.
Above you see a modified medium wave loop antenna plugged into the microphone port of a netbook running Adobe Audition V1.5 The frequencies in question are so low that were they to be sound waves, they would be audible to human ears, so I skipped worrying about intercepting radio waves and simply treated the signal from the loop stick as if it were an audio signal. The results validate the basic approach but of course better amplification and filtering will be needed. But this was my first result.
The two thin lines represent VLF radio transmissions at 17.2 KHz and 22.5 KHz. The 17.2 KHz may be the SAQ Alexanderson Alternator operated as a museum piece from Grimeton in Sweden. One of the first trans-atlantic radio systems created, today it operates as a UNESCO World Heritage Site. The signal at 22.5 KHz is unknown but possibly one of the military VLF transmitters here in Hawaii. There is enough of a result here to build a larger system (in my copious free time).