Rose contends that inscribing information and physically sending it to some location in deep space is more energy-efficient than pulsing it out on radio waves, which disperse as they travel.
"Think of a flashlight beam," Rose says. "Its intensity decreases as it gets farther from its source. The same is true of the beam of a laser pointer, though the distance is much longer. The unavoidable fact is that waves, both light and radio, disperse over distance, and over great distance, they disperse a lot."
Rose and Gregory Wright, a physicist, are co-authors of a paper titled, "Inscribed matter as an energy-efficient means of communication with an extraterrestrial civilization," which appears on the cover of the September issue of Nature. The paper grew out of Rose's work at the Wireless Information Network Laboratory (WINLAB) at Rutgers' School of Engineering. "Our original question was, 'How do you get the most bits per second over a wireless channel?'" Rose says. This led him to consider distance, and the "energy budget" required for sending a signal. The budget increases with distance, Rose contends, and the detectability of the signal diminishes. The less detectable a message is, the lower its speed.
In addition, Rose says, when waves pass a particular point, they've passed it for good. Potential recipients at that point might be unable to snag a passing message for any one of many reasons. They might not be listening. They might be extinct. So someone sending such a message would have to send it over and over to increase the chance of its being received. The energy budget goes up accordingly. A physical message, however, stays where it lands.
Rose is in favor of listening for that close encounter, but he thinks researchers should have their eyes open, too. Rose speculates that "messages" might be anything from actual text in a real language to (more likely) organic material embedded in an asteroid - or in the crater made by such an asteroid upon striking Earth. Messages - and Rose suggests there might be many of them, perhaps millions - might literally be at our feet. They might be awaiting our discovery on the moon, or on one of Jupiter's moons. They might be dramatic or mundane. A bottle floating in the ocean is just a bottle floating in the ocean - unless, upon closer inspection, it turns out to have a message in it.
Rose concedes that this idea may be hard to accept, but this difficulty arises from our concern about time. If the sender isn't concerned about reaching the recipient and getting an answer in his own lifetime, inscribing and sending is the way to go.
"If haste is unimportant, sending messages inscribed on some material can be strikingly more efficient than communicating by electromagnetic waves," Rose says.
Of course, E.T.'s choice of medium might be affected by how much he had to say. "Since messages require protection from cosmic radiation, and small messages might be difficult to find amid the clutter near a recipient, 'inscribed matter' is most effective for long, archival messages, as opposed to potentially short 'we exist' announcements," Rose says.