Given the number of stars in the universe, how arrogant to think ours is the only sun with a planet that supports life, and that it's the only solar system with intelligent life.
— Edward J. Weiler, NASA Director (Washington Post newspaper, 20 July 2008)
While I can’t disagree with the sentiment of Mr. Weiler’s statement, the bigger question remains – how likely is it that we will ever find evidence of other life in the universe, or be able to communicate with them if they do exist?
We tend to imagine that if there is alien life somewhere out there in the vast universe, they could be receiving our television broadcasts, and will eventually respond back to us. This was the premise of “Contact”, the blockbuster sci-fi movie written by Carl Sagan.
In the movie, Dr. Ellie Arroway (Jodie Foster) is heading up a SETI team (Search for ExtraTerrestrial Intelligence), and they detect a signal coming from a far-away star system. They quickly realize that the signal is one of our own TV programs, which is being re-broadcast back to us – and interleaved in between the frames of video are instructions from an alien civilization on how to make a spaceship to go visit them.
I really did enjoy this wonderful movie, but the realities of aliens receiving our TV signals isn’t quite as simple as it was portrayed.
Television broadcasts can be “terrestrial” (the traditional antenna tower constructed behind most TV stations, or high on a hill overlooking the city), or via satellite. Modern satellite systems are marvelous things. You just go to the store and buy a “dish”, which is about 20 inches in diameter, and point it up in the sky. Then you align it to the right satellite, and you have TV reception in glorious high definition!
The signal that the dish receives is not very powerful – somewhere in the range of a micro-watt of power (one millionth of a watt). However, you need to remember that you can put the antenna anywhere … in your front yard, in the back yard, on your roof; the network of satellites that broadcasts the signal to your house isn’t beaming a microwatt of power directly to your dish, it is putting out a microwatt of power for every 20-inch circular area across the entire United States! Only a very miniscule amount of the power transmitted More...