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08-07-2007, 04:52 AM #20
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If Humans simply disappeared one day...
Okay, the cosmos are anything but empty space. There are solar flares, solar wind, gamma rays, and the like, which are not background radiation from the Big Bang. Hell, a major problem which satellites and deep space probes face is electro-magnetic interference.
Originally Posted by NextLineIsMine
SPACE.com -- Can Aliens Find Us?
SPACE.com -- Listening for ET's TelevisionBottom line? With radio technology slightly more advanced than our own, Homo sapiens is detectable out to a distance of roughly 50 light-years.
F.06 How far away could we detect radio transmissions?OK, how strong is that signal by the time it reaches our putative alien audience at 55 light-years distance? Not very. The megawatt broadcast washes over ET's world with a power density of about 0.3 million million million million millionths of a watt per square meter, which is not exactly a scorching signal.
TV Beacons in Space - TIMEEven a 3000 meter diameter radio telescope could not detect the "I Love Lucy" TV show (re-runs) at a distance of 0.01 light years! It is only the narrowband high intensity emissions from Earth (narrowband radar generally) that will be detectable at significant ranges (greater than 1 LY).
(200 light years is still a far cry from trillions of light years)Sweeping the Universe. Unlike low-frequency radio waves, which are reflected back by the earth's ionosphere, UHF transmissions continue traveling in a straight line out into the farthest reaches of space. And unlike standard television waves, which penetrate into space but tend to be drowned out by cosmic radiation of about the same frequency, UHF broadcasts could eventually be detected as far off as 200 light years from earth.
Once again, narrowband transmissions pointed in one specific direction can travel great distances, but broadband television signals transmitted today will be dead before you die.
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