Re: A response to Rose and White's paper

[Michael Turner]

Larry writes: "Over his example of a milion years' travel time to cover a 1000 l.y. distance, the proper motions of both originating and target stars will have a large influence. This creates problems of propulsion and guidance (including mid-course corrections), and the service life of the control systems."   I suppose it means at worst finding an approximate solution to a multi-body problem, starting with the best approximations you can get of current star trajectories.  But surely the energy required to get up to even 1/1000th of c is vastly greater than that required for a few mid-course corrections.  Any propulsion and navigations problems originating from course correction will be very minor compared to those you have to think about for initial propulsion in the first place, and for landing somewhere in a star system that you probably couldn't even anatomize clearly when you first launched the craft.   "Rose mentions RNA as a particularlt dense method of encoding -- now consider how that might be subject to 'mutation' over a million years, even to such low-probability events as neutrino interaction, which cannot be shielded against, let alone cosmic rays and the occasional gamma ray burst."   The obvious approach is to use something like the coding technology used in the Deep Space Network. Error correcting codes do not vastly increase the size of a message.  As well, the package might contain devices that wake up periodically, re-read the message and regenerate it, including the ECC, so that there's a vanishingly small chance that it will be corrupted at all even with a high mutation rate.  Such message-regenerator devices might also be made self-repairing.  Building all of this into a small package seems like a forbidding task to us right now, perhaps, but ... well, as I type these words, every character painted on the screen consumes an amount of computer power that would've caused an early-sixties mainframe computer to sag and moan, and that computer would have consumed a room and lots of electricity.  And this change happened only in my lifetime.  The Drake Equation predicts that any civilization trying to communicate with us is likely to be much more technologically advanced than we are now.  By many thousands of years, in fact.  The bigger question may not be "could they do it if they wanted to?" but "would such intelligence want to do this?"   "The "persistence" of such encoded information now possibly includes exposure to atmospheric phenomena after a million-year journey through interstellar space -- assuming the package isn't damaged in the process of delivery."   This sounds sort of like the objections to the space elevator that run: "But what about those high winds?"  A tether than can hold against such astonishing forces isn't going to be whipped apart by mere winds.  Likewise, a package designed to survive a million years of traveling at high speed in interstellar space probably isn't facing its worst obstacle in encountering a planetary atmosphere.  If anything, it's facing a relatively predictable and controllable obstacle.   "Then there's the decoding process. The Voyager Record has pictorial instructions engraved on its casing. How might one render a similarly simple 'manual' for decoding RNA"   Why would you bother to make it "similarly simple"?  If civilizations have long enough lifespans to make SETI worthwhile in the first place, you're not missing many windows of opportunity if you make a few recipients scratch their heads for a year (or two centuries) because they don't know what RNA is yet (or haven't figured out yet that you can encode information in molecular chains.)  The length of time between the point where a civilization can contemplate scrutinizing their environment for signs of a message and the point where they can decode the message is going to be an eyeblink in its overall lifetime.  As well, an object that's smart enough navigate from one star system to another without forgetting anything imporant for a million years isn't likely to have much trouble announcing its presence if something intelligent approaches, and likewise won't have a problem making it clear that there's a message to be decoded.   Gee, it occurs to me I'm being awfully defensive about an idea that I consider a little ridiculous in the first place.  I think the main interesting use of such a device would be to create life, not communicate with it.  If some such package cruised into the solar system tomorrow, I think the first sign of ET intelligence would be Mars changing color as this gadget started replicating and terraforming it, having determined that our planet is already taken.  You have to admit that would get people's attention.   -michael   ----- Original Message ----- From: LARRY KLAES To: setipublic Cc: BioAstro ; europa Sent: Friday, September 03, 2004 3:05 AM Subject: A response to Rose and White's paper http://www.habitablezone.com/space/messages/341551.html   . . . within the next million years -- stick to radio. Rose's paper is here, which I found on his website. Discussion in the press (links at Rose's website, including an article in the NYT Science section by Dennis Overbye, one of my favorite popularizers of astronomy) makes repeated analogy to Clarke's monoliths in 2001: A Space Odyssey, yet fans of the film and book will recall that, as a communication device, the one on the Moon relied on an extradimensional energy burst to alert its constructors to its discovery (which also "bled" into the EM spectrum in our spacetime). Thse quotes are sequential (i.e., not cherry-picked), from the final paragraph of the paper's conclusion: Finally, for such long range channels, we have skirted the issue of what sort of messages one might want to send, how they might be detected or where they might be sent [28], [29]. The large delays associated with interstellar travel and the seeming fragility of species to cosmic insults suggests that an intelligent sender might construct messages ?for posterity? as opposed to for initiating a chat. That's an awful lot of skirting. I haven't read the entire paper yet, but I have the impression that Rose's energy efficiency calculations are a little too simplistic. Over his example of a milion years' travel time to cover a 1000 l.y. distance, the proper motions of both originating and target stars will have a large influence. This creates problems of propulsion and guidance (including mid-course corrections), and the service life of the control systems. On the other hand -- the "Voyager Record" is a perfect example -- is the concept of sending information packages Out There, and maybe someone will find them ... rather like finding, not a needle, but a single atom of platinum in a haystack. What seems most critical to me is what (elsewhere in the paper) Rose terms "hardening". Unfortunately for me, his reference [19], discussing theoretical limits of the information density on inscribed matter is unavailable (until I go to the library, since I don't have a subscription to Science). Nonetheless, it's fair to consider that the smaller each bit of information, the less energy required to alter it. Rose mentions RNA as a particularlt dense method of encoding -- now consider how that might be subject to 'mutation' over a million years, even to such low-probability events as neutrino interaction, which cannot be shielded against, let alone cosmic rays and the occasional gamma ray burst. One might also think of ?colonization? as a goal as well [30]. In both regards, one ostensible virtue of inscribed mass channels is that once the message arrives, it is persistent as compared to electromagnetic radiation which is transient and thus must be sent repeatedly in order to assure reception. "One the message arrives" - implying either [a] more propulsion and autonomous controls to place it in orbit around the target star (or a planet), or [b] propulsion, controls, decision algorithms to select a planet upon which to land, and a means of making that landing mechanically survivable. The "persistence" of such encoded information now possibly includes exposure to atmospheric phenomena after a million-year journey through interstellar space -- assuming the package isn't damaged in the process of delivery. Then there's the decoding process. The Voyager Record has pictorial instructions engraved on its casing. How might one render a similarly simple 'manual' for decoding RNA? Of course, constructing mass packets to be hearty, easily detected and/or self replicative seems well outside our current engineering ken. Nonetheless, the notion of mass packet delivery, undertaken initially to examine assumptions about energy tradeoffs in terrestrial communications, does raise interesting questions about terrestrial biological history and perhaps SETI/xenobiological studies as well. That's a little too far-fetched, even for me. But, I think his class had a lot of fun with this.