Christopher Rose and Gregory Wright, Inscribed matter as an energy-efficient means of communication with an extraterrestrial civilization, Nature 431, 47 - 49 (02 September 2004).
When sending information long distances electromagnetic radiation might not be the most energy-efficient way. Rose and Wright show that over interstellar distances it may make more sense to send packages launched at sub-relativistic speeds than to try to beam over messages, even when taking massive radiation shielding and redundancy into account. The only loss is time.
Their conclusions seem to mirror the ones in my Jupiter brain paper. Matter is such a dense storage medium that it trumps mere radiation as soon as distances get large.
However, one conclusion in the paper might be too pessimistic: the antenna size. The largest antenna they consider is Earth-sized. But if you can build an interstellar launch catapult, it wouldn't be that hard to launch a number of observatories across the solar system, expanding the antenna size by 6 orders of magnitude. That in turn expands the distances where radiation are effective by 6 orders of magnitude. That suddenly makes local calls within the galaxy efficient.
Posted by Anders at September 8, 2004 11:57 AM