Does man send any signal (such as electromagnetic radiation) to space to attract aliens?
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4$\begingroup$ Maybe you should add if this happens intentionally. I'd say yes, but maybe it's scarring them away. :) $\endgroup$– bastikCommented Aug 25, 2013 at 15:53
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3 Answers
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The first message in the history of humanity was: "Мир, Ленин, СССР". The English translation being, "World, Lenin, USSR".
A lot of people will try to bring up that "мир" actually has two meanings, the second one being "peace". My opinion is, that in this case, it only means "world", or in stricto sensu "Universe".
It was long ago, in 1962, when this radio message was sent in Morse code towards Venus. Unfortunately, no extraterrestrials were found there.
This message is the first radio broadcast for extraterrestrial civilizations in the history of mankind. The signal reflected from surface of Venus and was received 4 minutes 32.7 seconds (Nov 19) and 4 minutes 44.7 seconds (Nov 24) later.
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3$\begingroup$ Unfortunately, no extraterrestrials were found there. Why is that unfortunate? $\endgroup$– gerritCommented Aug 28, 2013 at 23:42
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6$\begingroup$ Arthur C. Clarke said: "Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying." $\endgroup$ Commented Aug 29, 2013 at 12:52
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Assuming that by signal you mean radio signals, there were many attempts.
All this has already been described in detail on Wikipedia, so I'm not inclined to repeat it. What you are looking for is available in these two pages:
- Active Search for Extra-Terrestrial Intelligence (Active SETI)
- Communication with Extraterrestrial Intelligence (CETI).
Probably the most famous example of such signal is the Arecibo Message, sent on November 16th 1974:
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Yes, unintentionally, all the time. Radio (incl. TV, etc.) propagate in a straight line from the transmitter. Some transmissions are reflected or absorbed by layers in the atmosphere (depending on frequency), but others leak into space. So there's a shell of radio transmissions around Earth with a radius of 127 light years, expanding at the rate of 1 ly/year.
Most are not powerful enough to be intelligible by the time they arrive in another star system, though.
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1$\begingroup$ Not even military radars are strong enough to be perceived as a coherent wave about 1 light year away, unless you happen to have a ludicrous sized dish at the other end that happens to be pointing in the right direction at precisely the right time. Otherwise S/N simply doesn't permit detection. And other carrier waves (inc. most military radars) are largely attenuated by Earth's atmosphere and ground. Even Seth Shostak (SETI) wrote some papers and recently reaffirmed how METI (active SETI) is largely benign. And some of those attempts were far stronger than anything we broadcast unwittingly. $\endgroup$ Commented Apr 21, 2015 at 16:09