Radio Bubble: alien couch potatoes? It's possible, thanks to escaping TV and radio signals

Natural History, Nov, 2001 by Neil deGrasse Tyson

As you might guess, the United States contributes more than any other nation to Earth's global television profile. An eavesdropping alien civilization would first detect our strong carrier signals. If the aliens continued to pay attention, they would notice periodic Doppler shifts (alternations between lower and higher frequencies) in these signals every twenty-four hours. They would also notice the signal getting stronger and weaker during the same time interval. The aliens might first conclude that a mysterious, though naturally occurring, radio loud-spot was rotating in and out of view. But if they managed to decode the modulations within the surrounding broadband signals, they would gain immediate access to elements of our culture.

Unlike sound waves, electromagnetic waves (including visible light and radio waves) do not require a medium to travel through. Indeed, they are happiest moving through the vacuum of space. So the time-honored flashing red sign in broadcast studios that says "On the Air" could justifiably read "Through the Space," a phrase that applies especially to the escaping TV and FM frequencies.

As the signals move away from Earth, they get weaker and weaker, ever more diluted by the growing sphere of space through which they travel. Eventually the signals drown in the ambient radio noise of the universe--noise from regions of star formation in the Milky Way, exotic galaxies, cosmic rays, and the big bang itself. These factors, more than any others, will limit the ability of a distant civilization to decode our way of life.

At current broadcast strengths from Earth, aliens using human technology would require a radio receiver 15 times the collecting area of the thousand-foot Arecibo radio telescope (the world's largest telescope) to detect a television station's carrier signal from a hundred light-years away. If they wanted to decode our programming information, and hence our culture, they would first need to compensate for the Doppler shifts caused by Earth's rotation on its axis and by its revolution around the Sun before they could lock onto a particular TV station. They would then need to have a detection capacity 10,000 times greater than that needed to detect the carrier. In radio-telescope terms, this amounts to a dish with a diameter about 400 times Arecibo's, or about seventy-five miles across.

If technologically proficient aliens are indeed intercepting our signals (with a suitably large and sensitive telescope) and if they are managing to decode the modulations, then the basic features of our culture are surely befuddling the anthropologists among them. As they watch us becoming a radio-transmitting planet, their attention might first be flagged by early episodes of The Howdy Doody Show. Once they knew to listen, they could then audit episodes of The Honeymooners and I Love Lucy and learn how typical human males and females interact. They might then assess our intelligence from episodes of Gomer Pyle or The Beverly Hillbillies and then, perhaps, from Hee Haw. If the aliens didn't just give up at this point, and if they chose to wait a few more years, they would learn a little more about human interactions from Archie Bunker in All in the Family. After a few more years of study, their knowledge would be further enriched by the odd characters in Seinfeld and, of course, the prime-time cartoon The Simpsons. (They would be spared the wisdom of the hit show Beavis and Butthead because it existed only as a cable program on MTV.) These cherished sitcoms were among the most popular shows of our time, each sustaining cross-generational exposure in the form of reruns. Mixed in among our cherished sitcoms would be the extensive, decade-long news footage of bloodshed during the Vietnam War, as well as coverage of Nicaragua, Iraq, Bosnia, and other military hot spots around the planet.