On Nov. 16, 1974, astronomer Frank Drake dedicated a new observatory in Arecibo, Puerto Rico, by sending humankind's first deliberate communication to extraterrestrials.
The message, made up of 1,679 seemingly random zeros and ones, was shorter than the first four paragraphs of this article, but it still took three minutes to send. While the message began its voyage to the cosmos--a 24,000 year trip to M-13, a cluster of stars in the constellation Hercules, to be exact--visiting dignitaries listened over a loudspeaker while each bit played as a short, high-pitched tone. Some participants later said it brought tears to their eyes.Humans have debated the best ways to contact our interstellar neighbors for centuries. In 1820, German mathematician Karl Friedrich Gauss proposed cutting an enormous right triangle into the Siberian pine forest, creating a monument to the Pythagorean theorem big enough to see from outer space. Twenty years later, Austrian astronomer Joseph von Littrow expanded on that idea, suggesting the excavation of huge trenches in the Sahara desert, which would be filled with kerosene and set ablaze. Flaming triangles, circles and squares would be a beacon to our solar neighbors, at least until the fire went out.
To a large extent, modern technologies have made these suggestions irrelevant. Since the 1920s, human radio and TV broadcasts have spammed the galaxy, and anyone listening has already gotten an earful. "In some sense, this is all academic, because we have been broadcasting to aliens for decades," says Seth Shostak, senior astronomer at the SETI Institute, a nonprofit organization dedicated to the search for extraterrestrial intelligence. "They're already watching Kate Smith and Kukla Fran and Howdy Doody."
But what if we decided we wanted to send a message with intent, something that will say more about us than an episode of The Love Boat? What's the best way to create a message that will be received, understood and useful?
The Arecibo broadcast represented one approach. Those 1,679 zeros and ones carried hidden meaning for any intelligent species who noticed that 1,679 is the product of two prime numbers, 73 and 23. Arrange the message in 73 rows of 23 numbers, and you get a picture painted in bits. ( Click here to see the decoded Arecibo message.) It was a novel approach, but the message was hidden, and it depended on aliens making leaps of logic in order to decipher it.
Arecibo wasn't the first time Drake pondered how to address an alien audience. In March 1972, a plaque he designed with legendary astronomer Carl Sagan was blasted into space on board the Pioneer 10 spacecraft. ( Click here to see the Pioneer Plaque.) A few years later, Drake and Sagan would team up again on a much more ambitious project, attaching a gold-plated record full of music and photos onto the two Voyager probes.
These efforts are notable because so few other attempts have been made to craft a message to alien civilizations. But as actual attempts at communication, the spacecraft fall flat. They're too small to notice and move too slowly. Far better to use a broadcast signal, which we can target at a specific star, and which moves at the speed of light.
We could use the same radio frequencies as the Arecibo message, but why not do something a little more dramatic? The universe is pretty transparent to optical light--that's how we can see far away galaxies. If we used a bank of high-powered lasers, we could beam a high-bandwidth message across the cosmos.
And we could do it with style. "One nice thing about light is that creatures develop eyes, and it would be possible to make optical radiation bright enough to see," says Paul Horowitz, a professor of physics at Harvard University. "That's an unmistakable signature. You look up, and there's a star, blinking in code, and the color's changing, too."
Next comes the question of what the message should say. Drake says if he could do it again, he might convene an international committee of scientists, artists, politicians and religious figures to produce a holographic movie about life on Earth.
Other researchers suggest that the best way to get an alien's attention is to send it a significant numeric pattern, perhaps prime numbers or the value of Pi. "Maybe the most fundamental way to initiate a message would be with mathematics," says Horowitz. "A lot of stuff will surely be understood by anybody, no matter what slime they're made out of, because it’s so basic."
The mathematical approach has its critics. "You're not going to send the value of Pi," says Shostak. "If aliens sent us the value of Pi, wouldn't you be disappointed? You learned that in seventh grade."
Instead, why not transmit everything we've got? "I would just send the entire contents of Google's servers," says Shostak. "To begin with, you don't have to worry about the fact that they don’t speak English, because there's a lot of redundancy, so they'll learn it. And every subject is in there. Sure, there's a lot of pornography, but that's human stuff, too."
Besides, it doesn't make sense to tease an alien civilization with just a "hello," considering that it could take millennia before we hear back from them. "It's like the Romans sent a message [to aliens] and we got the reply," says Shostak. "[The reply] was actually directed at Cicero, not at us. I just think that you would send as much info as the technology would allow on the assumption that you're not going to hear back."
The discussion might seem academic. But many astronomers are confident they'll detect an extraterrestrial intelligence in the next few decades, and when that happens, we better have an official reply ready, or risk being drowned out by the public.
"Once contact's been made, one of the first things that is going to happen is that everyone with a backyard antenna and the ability to wire up a transmitter is going to get online with their personal philosophies," says Shostak. "People will want to reply, and you can't stop them."
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