This week's quibble comes from the Oct. 14, 2008 edition of Geek Trivia, "Skies on the prize." NickNielsen used some cunning mathematics to explain why all those advertising messages we beam into space are money wasted, so far as the consumer extraterrestrial market is concerned.
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This week's quibble comes from the Oct. 14, 2008 edition of Geek Trivia, "Skies on the prize." Our old buddy NickNielsen used some cunning mathematics to explain why all those advertising messages we beam into space are money wasted, so far as the consumer extraterrestrial market is concerned:
"All radio signals, regardless of content, obey the inverse square law--the signal power decreases with the square of the distance. Basically, each time the distance from the antenna doubles, the signal strength is divided by four.
"In 'Earth' measures, a light year is 9.4607304725808 x 10^15 m (about 9.461 pm) or 5.878625373183 x 10^(12 + 849/1397) (nearly six trillion) miles. (http://www.nationmaster.com/encyclopedia/Light-year)
"For a 1,000 watt transmission, the signal strength at a distance of one light year is 1.1172507631287326873409989371953 x 10^-29 watts or a little more than .00001 yoctowatts (10^-24 watts). The most sensitive receiver of which I'm aware can't detect intelligence in signals with a strength of less than 1 picowatt (10^-12 watts). To achieve a 1 picowatt signal at one light year, the original signal would need to be 100,000,000,000,000,000 times stronger at 10^20 kilowatts (100 exawatts).
"The good news: ET isn't watching I Love Lucy or Survivor. The bad news (much as I hate to admit it): SETI is probably doomed to ultimate failure and we won't know it until ET lands."
Thanks for the dour dose of communications physics, Nick, but I choose to believe any ET that could build a faster-than-light spacecraft capable of visiting us also has better radio receivers that we do. (Also, hopefully, Orion crew women.) Keep the faith, Mr. Nielsen, and for the rest of you -- keep those quibbles coming!
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