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Number of ET Civilizations In Our Galaxy Is 37,964
KentuckyFC writes "The famous Drake equation calculates the number of advanced civilizations in our galaxy right now. But the result is hugely sensitive to the assumptions you make about factors such as the number of habitable planets that orbit a host star, how many of these actually develop life and what fraction of these go on to become intelligent etc. Disagreements about these figures leads to estimates for the number of advanced civilizations ranging from 10^-5 to 10^6. Now an astronomer in Scotland has worked out how to make the calculations more precise so that different theories about the origin of planets, life and civilizations can be compared. His calculations say that the rare-life hypothesis predicts only 361 advanced civilizations in the Milky Way now. However, the so-called tortoise and hare hypothesis predicts 31,573 and the theory of panspermia says that there ought to be 37,964 extraterrestrial civilizations more advanced than our own in the Milky Way."
Or there is of course, another possibility: That humans are the only "intelligent" species using radio transmission as a communications medium and that any other "intelligent" species is such a great distance away and/or in a region of space where we haven't been listening that we are unable to detect them.
--Stupid Sig Here--
That's 32767 and an overflow flag.
And get off my lawn.
No folly is more costly than the folly of intolerant idealism. - Winston Churchill
Sorry, but the logical fallacy police have to intervene in this one. Absence of evidence is indeed evidence of absence; however, it is not proof of absence. In this case, as has already been demonstrated, we would need significantly more evidence of absence before we could come to any sort of meaningful conclusion. The current evidence of absence is about the equivalent of saying we know there's not a large ET base on the surface of the bright side of the moon.
Further, there's nothing logically wrong with the pot calling the kettle black. The kettle is indeed black regardless of the color of the pot. It just makes the pot look dumb for trying to make fun of the kettle. It reminds me of this quote attributed to Jack Nicholson:
"My mother never saw the irony in calling me a son-of-a-bitch."
SWM seeks new sig for a brief fling
A terawatt signal radiating uniformly would produce 1e12 / (4*pi*(4e16)^2) w/m^2 = 5.0e-23 w/m^2. With a dish the size of Arecibo (7.3e4 m^2) that's -144 dBm (decibels referred to milliwatts). For comparison, the received GPS signal strength is ~ -133 dBm. With a slightly narrower bandwidth, or signal processing techniques that can work at lower SNR (eg looking for a carrier wave over extended periods -- exactly the sort of stuff SETI@home does) that extra order of magnitude isn't hard to come by.
Note that there are efforts ongoing to build larger area arrays (eg the square kilometer array), improve reciever electronics (chilling the front-end amplifier lowers the inherent amplifier thermal noise, for example), and improve signal processing techniques. Also, for certain types of transmission, the 1TW estimate isn't unreasonable -- Arecibo has radar transmitters with as much as 20TW effective isotropic power (lower total power, aimed at a small fraction of the sky). Given the right sort of source signal and extended observation, something like Arecibo could see some of our leakage signals, not just intentional transmissions.