By Morris Jones
In these high-tech times, most communications on Earth move very quickly, sometimes at the speed of light. Telecommunications and information technology have made it practical to quickly send messages around the world, and to practically any place in the world. We still have traditional postal systems, but their speed of delivery is modest compared to electronic systems. Thus, physical mail is sometimes dubbed "Snail Mail" for its slow pace.
Communication between civilizations in different parts of the galaxy faces similar issues. Since its inception as a modern science, the Search for Extraterrestrial Intelligence (SETI) has mostly focused on electromagnetic signals. This started with radio astronomy and has since branched out into Optical SETI, which involves the search for laser pulses with optical telescopes.
The engineering and principles of modern SETI make a lot of sense. Electromagnetic waves (including radio, light, and others) travel fast, and all at the speed of light. With current technology, we can't send anything faster than them. They are also easy to generate and detect. If we find electromagnetic communications so useful in human society, it seems logical to assume that an extraterrestrial civilization would also try such methods to reach us.
We could also consider exotic methods such as neutrino beams or gravity waves, but there's another method that isn't typically discussed in SETI and METI circles. Can we use Snail Mail in space?
Most SETI practitioners would immediately scoff, and for good reason. Despite their speed, it could still take centuries (or even longer) for a radio message to travel between two civilizations. But trying to "mail" a physical object across interstellar space would make this look like a short interval. It took roughly a decade to send the New Horizons spacecraft to Pluto, and that world is still in our own solar system. Getting a spacecraft or a package to another star system would potentially take hundreds of thousands of years with our present technology.
The time lapse is a real drag. And so is the targeting. A radio signal can be made to cover a fairly broad area, diverging as it travels. Like a vast net in space, it can cover many solar systems. But trying to find a relatively small physical object in deep space would be tricky. It could be almost impossible to locate it, even if you knew it was coming. Trying to launch it on a precise trajectory and keep it on that trajectory would also be difficult.
Sending Snail Mail across interstellar space seems difficult with our present technology. Right now, radio and optical have a massive lead over anything we can launch into space. But who knows what might be possible in the future?
We could imagine an advanced extraterrestrial civilization trying to send dozens or hundreds of small message packets into the universe, hoping that someone, somewhere, could eventually find one of them. If space transportation technology becomes very cheap and practical, this could be feasible. But even so, the odds of actually discovering such a package would still be small. Even if we found one, it is probable that the civilization that sent it would be extinct by the time we discovered their message. But their Snail Mail would be like a time capsule of their existence, and a legacy to the rest of the universe.
Before we completely dismiss the idea of Snail Mail in space, let's not forget that we have already tried it. Four spacecraft leaving our solar system carry messages with them. Pioneers 10 and 11 have simple pictorial plaques, and Voyagers 1 and 2 have complex multimedia messages encoded on gold records. Plans have been implemented to upload a METI message to the New Horizons spacecraft toward the end of its mission.
Snail Mail may not be the best way to communicate across the universe, but we shouldn't totally dismiss it.
Snail Mail in Space