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| Personal background |
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We are most definitely not alone.
N = N* fp ne fl fi fc fL
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N* represents the number of stars in the Milky Way Galaxy
Question: How many stars are in the Milky Way Galaxy?
Answer: Current estimates are 100 billion.
fp is the fraction of stars that have planets around them
Question: What percentage of stars have planetary systems?
Answer: Current estimates range from 20% to 50%.
ne is the number of planets per star that are capable of sustaining life
Question: For each star that does have a planetary system, how many planets are capable of sustaining life?
Answer: Current estimates range from 1 to 5.
fl is the fraction of planets in ne where life evolves
Question: On what percentage of the planets that are capable of sustaining life does life actually evolve?
Answer: Current estimates range from 100% (where life can evolve it will) down to close to 0%.
fi is the fraction of fl where intelligent life evolves
Question: On the planets where life does evolve, what percentage evolves intelligent life?
Answer: Estimates range from 100% (intelligence is such a survival advantage that it will certainly evolve) down to near 0%.
fc is the fraction of fi that communicate
Question: What percentage of intelligent races have the means and the desire to communicate?
Answer: 10% to 20%
fL is fraction of the planet\\\\\\'s life during which the communicating civilizations live
Question: For each civilization that does communicate, for what fraction of the planet\\\\\\'s life does the civilization survive?
Answer: This is the toughest of the questions. If we take Earth as an example, the expected lifetime of our Sun and the Earth is roughly 10 billion years. So far we\\\\\\'ve been communicating with radio waves for less than 100 years. How long will our civilization survive? Will we destroy ourselves in a few years like some predict or will we overcome our problems and survive for millennia? If we were destroyed tomorrow the answer to this question would be 1/100,000,000th. If we survive for 10,000 years the answer will be 1/1,000,000th.
When all of these variables are multiplied together when come up with:
N, the number of communicating civilizations in the galaxy.
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The real value of the Drake Equation is not in the answer itself, but the questions that are prompted when attempting to come up with an answer. Obviously there is a tremendous amount of guess work involved when filling in the variables. As we learn more from astronomy, biology, and other sciences, we\\\\\\'ll be able to better estimate the answers to the above questions.
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| Thoughts about SETI and SETI@home |
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Keep looking and we will find what we are looking for if we look hard enough.
“Radio waves travel at the speed of light. Nothing goes faster. At the right frequency they pass cleanly through interstellar space and through planetary atmospheres. If the largest radio/radar telescope on Earth were pointing at an equivalent telescope on a planet of another star, the two telescopes could be separated by thousands of light-years and still hear each other. For these reasons, existing radio telescopes are being used to see if anyone is sending us a message. So far, we have found nothing certain, but there have been tantalizing ‘events’ – signals recorded that satisfy all the criteria for extraterrestrial intelligence, except one: You turn the telescope back and point at that patch of sky again, minutes later, months later, years later, and the signal never repeats. We are only at the beginning of the search program. A really thorough search would take a decade or two. If extraterrestrial intelligence is found, then our view of the Universe and ourselves is changed forever. And if after a long and systematic search we find nothing, then we may have calibrated something of the rarity and preciousness of life on Earth. Either way, this is a search well worth doing.â€Â
Carl Sagan
(1934-1996)
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