Somewhere in the cosmos, 36 light years away from us in the direction of the Hercules constellation, a series of electromagnetic waves stretching across 30 million miles of space carries a message from Earth. Each of the 1,679 signals it contains falls in one of two frequencies – an FM signal that translates to a bunch of ones and zeroes.
This message originated in 1974, when it was broadcast from the Arecibo radio telescope in Puerto Rico to commemorate the facility's renovation. The authors of the message, Carl Sagan and SETI founder Frank Drake, hoped that any aliens who happened to receive it might notice that 1,679 is the product of two prime numbers, 23 and 73, and if you arrange all the zeroes and ones in a grid of 23 columns and 73 rows, you get a series of simple, ASCII-like pictures, including a double helix and a crude image of a person. Whether or not an alien civilization could crack the code, they would at least notice something funny about these FM signals. They're 10 million times stronger than the background noise from our sun.
But no extraterrestrials will even get the chance. The Arecibo transmission was aimed at a system 25,000 light years away that will have long since orbited out of the signal's path by the time it arrives in the vicinity. The odds of any two civilizations ever overlapping in time are extremely small. Even if we left the Arecibo telescope squealing out its signal until its power ran out and its hardware rusted, there's virtually no chance that the emanations would get anywhere in particular, and hang around long enough to be seen or heard. The only way we'll make contact is if we can make a beacon that keeps going for millions or billions of years after we're gone.
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