Let it not go unsaid that I firmly believe that life in the Universe is the rule rather than the exception. I propose a conservative ratio of one habitable world on which life is evolving for every one hundred suns in the galaxy. That means that there is the potential for life around a billion suns in this galaxy alone and there are literally countless billions of galaxies out there. The recent discoveries of planets orbiting suns outside our own solar system are encouraging. It is becoming apparent that the emergence of planetary bodies is a part of the natural life cycle of a star. Given that a planet's orbit occupies a favorable zone then life will probably generate in some form upon it. Our own history teaches us that if life exists at all then it will eventually develop civilizations and technologies.
Then why is it that after all these years of SETI (the Search for Extraterrestrial Life) we have yet to detect even the faintest radio signal barely hinting at intelligent life from one of these worlds? I am clearly of the opinion that the idea that we are the only habitable world in the Universe is a wholly untenable one. There is no reason at all to assume that we are alone. It is a selfish and self-aggrandizing notion, completely unacceptable.
Gliese 581C holds the greatest promise for life close to our world. And yet, SETI researchers have twice pointed their radio telescopes at that sun in the hope of detecting some kind of sign that there is intelligent life there with advanced communication technology. And they have come up empty. The star Gliese is about 20 light years from Sol.
I'm not concerned that we are getting no results from SETI because I believe that there is a good reason for that. Around the solar system wherein we dwell there is a huge region occupied by a "dust" cloud known as the Oort cloud. The following is extracted from a web page describing the Oort cloud:
"Typical noontime temperatures are four degrees Celsius above absolute zero. As temperatures move toward absolute zero, the kinetic energy of the molecules approach a finite value. Absolute zero should not be considered a state of zero energy without motion. There still remains some molecular energy, although it is at a minimum, at absolute zero."
In light of the above information alone, one can only be skeptical as to whether a radio transmission from many light years away with a limited source of energy to begin with can even penetrate this region outside our solar system. The presence of all that ultra-cold distributed mass that this medium represents will most certainly subject intelligent radio signals to attenuating influences. The effect that all those objects and particles would have on the quality of coherent radio transmissions can be compared to the ghosting of our broadcast TV images bouncing around tall buildings in our immediate environment when we are using simple rabbit ears to pick them up, only their effects would be exponentially more severe. Not only that, but even from the planet Pluto the sun is barely distinguishable from other stars and the sun is a source of great energy, but not even enough to power solar cells from that distance and probes that are exploring that remote edge of the solar system rely on radioisotope thermoelectric generators. Radio signals which we are expecting to receive from intelligent sources by comparison are extremely weak signals compared to the power of a star. Even if we were able to separate intelligent information from the mumbo-jumbo that we would otherwise regard as chaotic EM wave activity we would have to know precisely the nature of the information that we are trying to extract and thus far we haven't communicated with any ET's who might be able to tell us anything about that.
When we attain that stage of space exploration which sees us sending probes to explore neighboring stars we will no doubt require strategically placed transponders discretely placed en route which serve no other purpose other than to boost the signal strength of transmitted data from those probes as they travel ever farther away from us. About three quarters of the way to Toronto from London in Southwestern Ontario I am no longer able to pick up The Hawk on the FM dial, which transmits from Woodstock. Satellite signals aren't even as strong.
I think it naive of us to assume that we can tap into the broadcasts enjoyed by the inhabitants of a world around a star twenty light years away. All this distance between us and that moat around the solar system called the Oort Cloud serve but to isolate us, and no amount of searching for extraterrestrial life in the way that SETI is doing it will meet with any kind of success, in my opinion. Prove me wrong.