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

Natural History, Nov, 2001 by Neil deGrasse Tyson

After watching fifty years of television, the aliens could draw no other conclusion but that most humans are neurotic, death-hungry, dysfunctional idiots.

In this era of cable TV, even broadcast signals that might otherwise have escaped the atmosphere are now delivered via wires directly to our homes. If this trend continues, there may come a time when television is no longer a broadcast medium, causing our tube-watching aliens to wonder whether our species had gone extinct.

For better or for worse, however, TV signals are not the only ones from Earth that aliens might decode. Anytime we communicate with our astronauts or our space probes, all signals that do not hit the craft's receiver are lost in space forever, though the efficiency of such communication has been greatly improved by modern methods of signal compression. In the digital era, it's all about bytes per second. If you devised a clever algorithm that compressed your signal by a factor of ten, you could communicate ten times more efficiently, provided the person or machine on the receiving end of the signal knew how to undo your secret signal. Modern examples of compression utilities include those that enable fast modems, MP3 acoustic recordings, JPEG images, and MPEG movies for your computer.

The only radio signal that cannot be compressed is one that contains completely random information, making it indistinguishable from static. And the more you compress a signal, the more random it looks to someone who intercepts it. A perfectly compressed signal will, in fact, be indistinguishable from static to everyone except the person with the knowledge and resources to decompress it. What does all this mean? If a culture is sufficiently advanced and efficient, then evidence of its intelligence might just disappear completely from the highways of cosmic gossip.

Ever since the invention of electric light, human culture has also created a visible bubble. Our nighttime signature has slowly changed from tungsten incandescence to other sources of light, including neon from billboards and sodium from the widespread use of sodium vapor lamps for streetlights. But apart from the Morse code flashed by shuttered lamps from the decks of ships, we typically do not send visible light through the air to carry signals, so our visual bubble isn't interesting. It's also hopelessly lost in the visible-light glare of our Sun.

Rather than let aliens listen to our embarrassing TV shows, why not send them a signal of our own choosing, demonstrating how intelligent and peace-loving we are? This was first done in the form of engraved gold plaques affixed to the sides of four unmanned planetary probes: Pioneer 10 and 11 and Voyager 1 and 2. All four plaques display pictograms conveying some basic science and our location in the Milky Way Galaxy. The two Voyager plaques also contain audio statements about the kindness of our species. Traveling at 50,000 miles per hour--a speed in excess of the solar system's escape velocity--these spacecraft are moving through interplanetary space at quite a clip. But compared with the speed of light, they're ridiculously slow and won't get to the nearby stars for another 100,000 years. These probes represent our "spacecraft bubble." Don't wait up for them.