Astrophage is not only for science fiction
While bestselling author of The Martian, Andy Weir’s recent novel, Project Hail Mary, is the best known use of the word, the concept of astrophage goes back at least 40 years. The name means “star eater” in Greek.
In a 1982 paper published by the Royal Society called “Models of Interstellar Exploration”, David Stephenson proposes that in order to explore the galaxy we must be capable of building probes that are Von Neumann machines, machines capable of reproducing themselves. Moreover, these machines must not make exact copies of themselves. They must learn and adapt, using information they have already gathered to improve on themselves.
Sound scary? You haven’t heard anything yet.
He furthermore argues that in order to obtain the necessary power and materials to reproduce exponentially and reach appreciable fractions of the speed of light to travel between the stars, these probes would be constantly hungry, looking for new energy sources. He suggests that they would need to “metabolize”, meaning eat, “asteroids…satellites, planets, and eventually the stars themselves.”
He suggests that if an alien species had constructed such a fleet of probes already,
the distribution of stellar types in a galaxy will be distorted by the extraction of either metals for new probes, or light elements for fuel from the stellar atmospheres, and the limit of this course of development is that a galaxy could be destroyed by an internally generated wave of astrophage probes within a period that is short compared with the lifetime of a galaxy. If this is the general form of interstellar exploration then, at the present time, we will be unique in the Universe, since any culture that launches interstellar probes will be destroyed as the stars around it are distorted and then wholly reduced to new probes.
[Emphasis added]
Essentially, he is saying that if this is the typical way you explore the galaxy, you would either see whole galaxies destroyed by this method or there is nobody out there to do it.
I guess that leaves it up to us.
I certainly hope no interstellar capable species is this crazy. If global warming is bad, consider galactic death as a whole new level of environmental destruction.
Thankfully, Stephenson doesn’t think this is the only way to explore the galaxy for he recognizes that
Launching self-adapting probes and then regarding them as independent intelligent beings, would be risking future destruction, for there is a block of information that could be lost from the programme of a replicating probe without the probe ceasing to function, and that is the memory of the inviolable system
of the originating culture.
Basically, once you open Pandora’s box and allow an interstellar capable, star eating organism to evolve, there is no guarantee it won’t come home and eat its home star no matter how carefully you programmed it not to.
Stephenson suggests that such exponential expansion models of interstellar exploration would be either potentially self-destructive or yield too little value to be worthwhile. Consider that there is little purpose in gathering information about a star system while you are in the process of destroying it.
Indeed, he suggests that the best way to explore star systems is to do so passively, not interacting with the subjects at all, let alone eating their star. He explores the possibility that the Earth might be under such scrutiny already, referring to a 1973 theory that the Earth is a galactic zoo.
If the Earth is a galactic zoo, one wonders if there are zookeepers, and, if so whether they would might doing something about all this species extinction and habitat destruction we are currently engaged in.
More likely we would not be a zoo, not for another species enjoyment, but rather a way for them to study us in the “wild”. And like wildlife photographers who don’t stop the lions from eating the gazelles no matter how sad it looks, our alien watchers will most likely be perfectly fine with human beings destroying ourselves. After all, the Earth itself will be just fine, with a brand new biome with in a few tens of thousands of years of our demise.
In any case, Stephenson suggests that it is far more valuable to observe one information rich planet, like the Earth, rather than send out countless probes to strip mine and destroy simpler systems that might be about as complex as a rock.
While at the time of his writing, in 1982, no exoplanets had yet been discovered, we now know that the galaxy is full of planets that could potentially be visited and observed. Yet, supposing we were to carry out his program of exploration, how would we choose which one?
It seems as if an exponential model would be incredibly resource intensive and destructive. We would be far more likely to choose a handful of planets, and the ones that we are most likely to choose are those that most resemble the Earth.
This works both ways. If an alien species on an Earth-like world were to see our planet across the vastness of space, how likely would it be that they would want to send probes here? And if they did, would they want to interact with us?
It seems as though the benefit of interstellar exploration is information gathering, not trade or cooperation. After all, what would we need that for given the vast distances between us? The energy needed to pass goods back and forth would be prohibitive, and cooperation is only needed if we were somehow using the same resources. We could exchange information of course. So far no alien communications so if they are out there they have no interest in talking to us or they don’t know we are here.
Expansion of the species is a possible reason too. It seems more likely, however, that we, looking for a planet to colonize, would try to find one that has no intelligent life. Indeed, that might be the purpose of sending probes in the first place, to find Earth-like worlds that have no intelligent species. After all, Earth had no technological species for billions of years until humans showed up, so the possibility seems more likely than not.
Could it be that extraterrestrial species leave us alone precisely because we are intelligent and technological? What about before we evolved? Why were there none here then?
Of course, there may have been. How would we know if aliens were here millions of years ago? We would have had to find their fossils or technology.
Absence of evidence is not evidence of absence. Then again, the odds may just be very, very low for intelligent, technological life to evolve at all and then to visit our planet. We may find that we have to visit millions of Earth-like worlds before finding one with technological species. That could just be too much in terms of resources to achieve, so it is just unlikely.
The astrophage dilemma puts limits on what we or any other species can achieve. Energy of stars may be called “renewable” now but once you start exponentially reproducing and traveling between stars, it no longer is. If there is no low energy but quick way to go between stars, then we as a species may never encounter another intelligent one.
Or we could be a lab for a vastly more intelligent species. We might never know.
Stephenson, David G. “Models of interstellar exploration.” Quarterly Journal of the Royal Astronomical Society 23 (1982): 236.
Ball, John A. “The zoo hypothesis.” Icarus 19.3 (1973): 347–349.