Centauri Dreams was amazed to realize that almost two years have passed since Christopher Rose and Gregory Wright posed a bold challenge to SETI researchers. In an article in the September 2 (2004) issue of Nature (a cover story, no less), the duo suggested that we are more likely to achieve extraterrestrial contact through artifacts — organic material embedded in an asteroid or comet, say — than through radio or optics. Larry Klaes, posting a link in a comment here on the Rose/Wright discussion, recently jogged my memory about this article, which deserves a renewed look.
Rose (Rutgers University) is a professor of electrical and computer engineering; his work with wireless technologies convinced him that “…it’s often MUCH (many many orders of magnitude) better from an energy use perspective (and perhaps from others like message persistence at the destination) to write a message down in some medium and LITERALLY toss it to the recipient than it is to radiate the message electromagnetically — assuming delay beyond light transit time can be tolerated.” He and physicist Wright (Antiope Associates) explored this notion in a piece that should remain required reading for anyone serious about the SETI hunt. They maintain current work on the idea on their Cosmic Communications page, from which the above quote is drawn.
The problem with artifacts, of course, is time. If we’re in a hurry, then we want to get the word out (or receive it) the fastest way possible, and with our current technology, that means working via radio or optics at the speed of light. But if we can extend our thinking to messages not so much for conversation as for archival purposes, recording the great works of a civilization (think of the Voyager golden discs), then imagine sending a highly compressed matter packet on a journey of millions of years. And imagine looking for such messages here.
From the original paper:
Any message presumably arrived after the Solar System became habitable (that is, after most of the protoplanetary debris had cleared), so whatever carried the message would be less eroded by impacts than an asteroid. Interplanetary radar could search for objects with anomalously smooth radar signatures. Alternatively, a message could have a retrore?ector attached to produce an anomalously large radar cross-section. Of course, an even simpler strategy is to use a powerful radio beam to illuminate these regions and see whether anything answers back. More active message types (ecological seeds or probes) are also conceivable, but are not necessary to exploit inscribed-matter ef?ciency.
Shades of Scottish astronomer Duncan Lunan, who once discussed a ‘phantom’ radio echo from the outer Solar System as a possible return signal from a space probe from Epsilon Bootes! I’m glad Larry noted Rose and Wright’s work in his recent comment, as it was apropos of another proposal to fling matter at a distant star, namely, a relativistic probe to Alpha Centauri whose effects upon the presumed debris disk there would announce its arrival. Who is to say that such objects have not come to our own Solar System, perhaps in far more complex form, with the obvious conclusion that we may be more likely to find evidence of extraterrestrials in nearby space than by trying to detect anomalous radio signals from other stars or looking for optical beacons.
Evidence for ET in a grain of sand? I find it a beautiful concept. The older SETI paradigms benefit when we bring such robust questioning to their premises. You can learn more about Christopher Rose and Gregory Wright on their respective Web sites. Centauri Dreams‘ original 2004 story on Rose and Wright’s work is here.
Nature reproduced the Voyager Record cover upside down –
now ETI will never be able to decode the record!
Hi Guys
One thing I mentioned to one of the researchers at the time was that the energy cost of launching a cairn-probe drops to zero if you use either sunlight or the solar-wind as the propulsive force. Ultra-light solar sails launched from 0.01 AU can reach 0.01 C easily, thus making the journey x10 quicker than the 0.001 c probes they assumed.
Adam
Another point they make in conclusion…
Our results suggest that carefully searching our own planetary
backyard may be as likely to reveal evidence of extraterrestrial
civilizations as studying distant stars through telescopes.
…which should be non-controversial based on a very minor extrapolation of current technology. Radio/optical SETI should be on equal footing with physical Searchs for Extra-Terrestrial Artefacts (SETA), as Freitas, Boyce, Bracewell, and now these authors, have all rightly pointed out.
The fact that reasonable extrapolations of nanotech, carbon nanotube solar sails and AI make self-intelligent monitoring/messaging probes even more logical and likely is just icing on the cake.
BTW Chris Boyce’s “Extraterrestrial Encounter” discussed SETA in the form of von Neumann Machines (vNMs) sent out to self-reproduce and monitor/explore the stars of the Galaxy. At the same time Frank Tipler began upsetting the Orthodox SETIist faithful by claiming the non-observation of vNMs meant there were no other technological intelligences in the Galaxy, if not the whole Hubble radius.
In reply Boyce computed the expected average number and mass of vNMs as follows:
M = m.T^2./(2.R1.R2)
..where m is the average mass, T the solar system’s lifetime, R1 the rate of arrival, R2 the rate of reproduction. He assumed that vNMs would not be reproducing uncontrollably, but merely creating a couple more probes to venture to new systems. If an average vNM weighed one million tons and arrived and reproduced every decade then about 10^26 kg (30 Earth masses) of vNMs would have been produced over the solar system’s lifespan. While this seems excessive there’s a lot of room in the Kuiper Belt. Also the Belt itself has shed 99% of its mass over solar time, a process perhaps utilised by vNMs?
I’ve got Boyce’s book here and have been meaning to get to it for some time now. Thanks for jogging me on this. There’s so much good material that’s getting lost in the stack due to the pace of incoming discoveries!
Glad to hear it. Chris’s book is an under-rated classic. Shame he died not long after he first got online, but I feel privileged that I corresponded with him and he liked one of my articles enough to feature it.
Of course the baseline vNM might be a lot lighter than he imagined in the late 70s. A 1,000 ton vNM might be enough – or lighter, if nanotech can be made reliable over cosmic time. In which case the mass used by replicating probes would be virtually undetectable.
A point made by a correspondent on the “Habitable Zone” discussion board a while ago: Megayear old starships, after meteoritic wear-and-tear, could look a lot like metallic asteroids. A well used “bumper shield”, or even massive throwaway engine modules for fusion drives after in space ‘erosion’, would be like an asteroid.
Finally Zubrin has already suggested that bacteria might literally be vNMs ‘created’ aeons ago to explore and seed the Galaxy. I wonder what would count as a message return to their point of origin?