The problem of perspective haunts SETI, and in particular that branch of SETI that has been labeled Dysonian. This discipline, based on Freeman Dyson’s original notion of spheres of power-gathering technology enclosing a star, has given rise to the ongoing search for artifacts in our astronomical data. The fuss over KIC 8462852 (Boyajian’s Star) a few years back involved the possibility that it was orbited by a megastructure of some kind, and thus a demonstration of advanced technology. Jason Wright and team at Penn State have led searches, covered in these pages, for evidence of Dyson spheres in other galaxies. The Dysonian search continues to widen.
I cite a problem of perspective in that we have no real notion of what we might find if we finally locate signs of extraterrestrial builders in our data. It’s so comfortable to be a carbon-based biped, but the entities we’re trying to locate may have other ways of evolving. Clément Vidal, a French philosopher and one of the most creative thinkers that SETI has yet produced, likes to talk not about carbon or silicon but rather ‘substrates.’ Where, in other words, might intelligence eventually land, and is that likely to be a matter of chemistry and biology or simple energy?
Vidal is currently at the UC Berkeley SETI Research Center, though he has deeper roots at the Free University of Brussels, from which he created his remarkable The Beginning and the End (Springer, 2014), along with a string of other publications. Try to come up with a definition of life and you may well emerge with something like this: Matter and energy in cyclical relationship using energy drawn from the environment to increase order in the system. I think that was Vidal’s starting point; it’s drawn from Gerald Feinberg and Robert Shapiro in Life Beyond Earth, Morrow 1980). No DNA there. No water. No carbon. Instead, we’re addressing the basic mechanism at work. In how many ways can it occur?
As Vidal reminded the audience at the recent Interstellar Research Group symposium in Montreal (video here), we are even now, at our paltry 0.72 rank in the Kardashev scale, creating increasingly interesting software that at least mimics intelligence to a rather high order. Making further advances that may exceed human intelligence is conceivably a matter of mere decades. If we consider intelligence embedded in a substrate of some kind, it makes sense that our planet may house fewer biological beings in the distant future than creatures we can call ‘artilects.’
The silicon-based outcome has been explored by thinkers like Martin Rees and Paul Davies in the recent literature. But the ramifications go much further than this. If we consider life as critically embedded in energy flows, the notion of life upon a neutron star swims into the realm of possibility. Frank Drake is one scientist who wrote about such things, as did Robert Forward in his novel Dragon’s Egg (Ballantine, 1980). If the underlying biology is of less importance and matter/energy interactions take precedence, we can further consider concepts like intelligence appearing wherever these interactions are at their most intense. Vidal has explored close binary systems as places where a civilization might mine energy, and for all we know, extract it to support a cognitive existence far removed from our notion of a habitable zone.
What about stars themselves? Greg Matloff has pointed to the low temperatures of red dwarf stars as allowing molecular interactions in which a primitive form of intelligence might emerge. Olaf Stapledon dreamed up civilizations using stellar energies in novel ways in Star Maker (Methuen, 1937) and mused on the emergence of stellar awareness. At Montreal, Vidal presented recent work on how an advanced civilization – in whatever substrate – might deploy a star orbited closely by a neutron star or black hole as a system of propulsion, with the ‘evaporation’ from the host star flowing to the compact companion and being directed by timing the pulsations to coincide with the orbital position of each. Far beyond our technologies, but then we’re at 0.72, as opposed to Kardashev civilizations at the far end of Kardashev II.
We have no idea how likely it is that such entities could emerge, but consider this. Charles Lineweaver’s work at Australian National University shows that the average Earth-like planet in the galaxy is on the order of 1.8 billion years older than Earth. The Serbian astronomer and writer Milan Ćirković has made the further point that this 1.8 billion year head-start is only an average. There must be planets considerably more than 1.8 billion years older than ours, and that makes for quite a few millennia for intelligence to develop and technologies to flourish.
Our first encounter with another civilization, then, is almost certainly going to be with one far older than our own. What, then, might we find one day in our astronomical data? I’ve quoted Vidal on this in the past and want to cite the same passage from The Beginning and the End today:
We need not be overcautious in our astrobiological speculations. Quite the contrary, we must push them to their extreme limits if we want to glimpse what such advanced civilizations could look like. Naturally, such an ambitious search should be balanced with considered conclusions. Furthermore, given our total ignorance of such civilizations, it remains wise to encourage and maintain a wide variety of search strategies. A commitment to observation, to the scientific method, and to the most general scientific theories remains our best touchstone.
The specific speculation Vidal tantalized the crowd with at Montreal is one he calls the ‘spider stellar engine,’ about which a quick word. Two types of ‘spider engines’ get his attention, the ‘redback’ and the ‘black widow.’ I assume Vidal is not necessarily an arachnophile, but rather a man aware of the current astrophysical jargon about extreme objects and pulsar binaries in particular. A redback refers to a rapidly rotating neutron star in tight orbit around a star massing up to 0.6 solar masses. A black widow has a much smaller companion star, and the term spider simply refers to the fact that the pulsar’s gravity draws material away from the larger star.
The larger star in such systems can be, spider-like, completely consumed, a useful marker as we study effects such as accretion disks and mass transfer between the two objects. Here is the energy gradient we are looking for in the question of a basic life definition, one that can be exploited by any beings that want to take advantage of it. A long-lived Kardashev II civilization, having feasted on the host star for its energies, could use what is left of the dwindling star at the end of its life to move to another host. The question for astronomers as well as philosophers is whether such a system would throw an observational signal that is detectable, and the question at this point remains unanswered.
Image; An illustrated view of a black widow pulsar and its stellar companion. The pulsar’s gamma-ray emissions (magenta) strongly heat the facing side of the star (orange). The pulsar is gradually evaporating its partner. ZTF J1406+1222, has the shortest orbital period yet identified, with the pulsar and companion star circling each other every 62 minutes. Credit: NASA Goddard Space Flight Center/Cruz deWilde.
We do have some interesting systems to watch, however. Vidal cites the pulsar PSR B1957+20 as having pulsations between host star and pulsar that match the orbital period, but notes that of course there are other ways of explaining this effect. We may want to include this particular signature as an item to look for in our pulsar work related to SETI, however. Meanwhile, the question of stellar propulsion (I think also of the ‘Shkadov thruster,’ another type of hypothesized stellar engine), explored by Vidal in his Montreal talk, yields precedence to the broader question with which we began. Are our perspectives sufficient to look for the kind of astronomical signatures that might be pointing toward forms of life almost unimaginably beyond our own?