Living a long time forces decisions that could otherwise be ignored. This is true of individuals as well as societies, but let’s think in terms of the individual human being. Getting older creates survival scenarios as simple as ensuring safety and nutrition for the elderly. But let’s extend lifetimes to centuries and beyond. In this thought experiment, we create a society of people so long-lived that their personal planning takes in events like a possible asteroid strike in 200 years. A person who could live for a billion years has to think in terms of surviving a dying Sun engulfing his or her planet.
If we assume a kind of immortality, the individual and the society merge in terms of their key concerns. It’s hard to imagine biological beings living for lifetimes like these, but as we’ve often considered in these pages, non-biological machine intelligence, constantly upgrading and improving itself, should be able to pull it off. Because we know of no extraterrestrial civilizations, we can only speculate, but the speculation is a good way to override our anthropomorphic prejudices. And it’s safe to say that any being or society will try to preserve itself in the event of local catastrophe.
Thus the needed insurance of interstellar migration, which philosopher Clément Vidal (Center Leo Apostel, Vrije Universiteit Brussel, Belgium) thinks might involve journeys vast enough to reach places where stars are as plentiful as in the globular clusters surrounding the Milky Way’s hub. Or galactic center, where resources abound and the need for frequent migrations is thus eased. If a culture like this spreads life through its own variant of panspermia, so much the better. I leave the motivations of a machine culture spreading biological life to science fiction authors, but believe me, there’s a cool plot in there somewhere. Someone should run with it.
Vidal’s idea of a stellar engine seizes on an unusual astronomical object, the so-called spider pulsar. We looked briefly at these last time, but let’s dig deeper. We imagine a civilization (Vidal calls them ‘stellivores’) that uses a low-mass star in its home system as a source of fuel, gradually consuming the star’s energies by accretion. So far so good, as we know that accretion is a well established phenomenon. It occurs, for example, in the formation of a Type 1a supernova, where a white dwarf reaches the Chandrasekhar limit (1.4 solar masses or so), drawing in material from a companion red giant through the process. Soon we have runaway nuclear fusion and a bright new object for astronomers to study.
A spider pulsar, a one millisecond pulsar with a very low-mass companion star, can interact not just through accretion but in some cases through evaporation. In reading Vidal’s new paper, I’ve been puzzled by this process, which actually can alternate with accretion in some instances. Things get complicated and quite interesting. Vidal explained in an email that evaporation becomes the primary process when a neutron star has a strong wind that actually quenches accretion and causes the move toward evaporation. Adds Vidal:
The astrophysical reason this would happen is after a long accretion journey, the companion star would get lighter and lighter, the orbit would shrink, up to the point where it is exposed to the strong pulsar wind and radiation. Then the dynamics would switch from accretion to evaporation. A subclass of (redback) spider pulsars, transitional millisecond pulsars, have their accretion that starts and stops abruptly. This is a fascinating phenomenology that has been studied intensively.
And indeed it has, as witness, for example, Baglio et al., “Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038” (citation below), where I read:
Transitional millisecond pulsars are an emerging class of sources that link low-mass X-ray binaries to millisecond radio pulsars in binary systems. These pulsars alternate between a radio pulsar state and an active low-luminosity X-ray disc state. During the active state, these sources exhibit two distinct emission modes (high and low) that alternate unpredictably, abruptly, and incessantly. X-ray to optical pulsations are observed only during the high mode. The root cause of this puzzling behaviour remains elusive.
But back to spider pulsar terminology. You probably noticed the reference to ‘redback’ pulsars. Astronomers divide spider pulsars into black widows, where the companion star is in the range of 0.01 to 0.1 stellar masses, and redbacks, where the companion star mass is between 0.1 and 0.7 stellar masses. Again, the phenomenon Vidal homes in on is evaporation, and it is at the core of the concept of using such a system as an engine. Suppose we look at a transition millisecond pulsar – one of those switching between emission modes – and consider it within the possibility that it is an engine.
Asymmetric heating could be our technosignature as a millisecond pulsar adjusts the heat of its companion star by moving between accretion and evaporation modes to perform, for example, steering maneuvers outside the orbital plane. Asymmetric heating in varying accretion and evaporation phases can compensate for increases in orbital separation. In Vidal’s view, the goal of the binary stellar engine might be to capture a new star whose energies can now be used to supplant the depleted companion and supply the needs of the engine’s creators. Thus the civilization travels to a new star. We imagine a billion-year culture in constant journey mode in search of energy, with the entire galaxy in range.
When we find objects in our data that show transitional millisecond pulsars in configurations that are suggestive, how do we distinguish between technological activity and natural phenomena? As with all technosignatures, it’s not an easy call. As Vidal notes in his email: “Now the game is to make predictions starting with (1) natural, astrophysical hypotheses and models, and (2) artificial, intelligent, “spider stellar engine” hypotheses and models, and see which predictions turn out to be correct.”
Image: This is Figure 1 from the paper. Caption: Four steering configurations of the binary stellar engine. Figures (a-c) are top views, face on, while figure (d) is side on. In situation (a) the stellar engine is accelerating or cruising; in situation (b), assuming the system velocity is towards the top, the thrust creates a force towards the left; in situation (c), assuming the system velocity is towards the top, the thrust creates a decelerating force. Situation (d) changes the orbital plane by asymmetric heating of the companion, which creates a lifting force in relation to the orbital plane. Note that the pulsar size and orbital separation are not to scale.
The mechanics of acceleration, steering and deceleration are intricate and fully described in the paper, which also includes information on other types of stellar engines going back to the original Shkadov concept – that chart is fascinating. In addition the paper analyzes candidate stellar engines that can be investigated for possible signs of intelligent control. But notice what kind of civilization we may be talking about here. After all, the payload of a spider engine is the millisecond pulsar, the propellant the low-mass companion star. We are thus considering postbiological intelligence on the neutron star itself. I want to quote Vidal’s email on this subject:
…[W]hat really matters is not the hardware of life, but what it does, its software, its functions. Recently we’ve seen with large language models that some form of intelligence can run on computer hardware. Of course, we could change this hardware multiple times and still have the same ChatGPT answering our questions. Life on Earth started with biochemical reactions, now we use semiconductor technology to process data, and we might see optical or quantum hardware taking over in the near future. If a civilization is on a billion-year long track to optimize its hardware and makes the most of the computational capacity of matter in the universe, it would likely continue to improve its hardware using more and more compact, high energy solutions such as nuclear reactions or subnuclear reactions (i.e. neutron star stuff). This is the level I imagine those stellivores are at. So, no planet, no individual traveler. Rather an integrated organism organized around high energy (sub)-nuclear reactions. It might still have some sub-organizations like species, nations, etc. but these would be at extremely small scales and impossible for us to detect.
As with all Vidal’s work, this paper is intricate and deeply researched. About spider engine maneuvering I have had the time only to cover the basics, and encourage interested readers to go to the paper, and also to mine the background laid out in Vidal’s magisterial 2014 title The Beginning and the End: The Meaning of Life in a Cosmological Perspective (Springer). The search for technosignatures demands moving far beyond the assumptions ingrained in our perspective as a species in technological infancy. No one works this turf better and with more elegance than Clément Vidal.
The paper is Vidal, “The Spider Stellar Engine: a Fully Steerable Extraterrestrial Design?” Journal of the British Interplanetary Society Vol. 77 (2024), 156-166 (full text). The Baglio paper is “Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038,” Astronomy & Astrophysics Vol. 677, A30 (September 2023). Abstract. See also Papitto et al., “Transitional Millisecond Pulsars,” in Millisecond Pulsars, edited by Sudip Bhattacharyya, Alessandro Papitto, and Dipankar Bhattacharya, 157–200. Astrophysics and Space Science Library. Cham: Springer International Publishing.
A billion years is a really long time. Planets have often been simulated to move based on orbital and tidal resonance, solar wind, even radiation pressure I think. If a planet the size of Earth is wrapped in a Ceres-mass ring system extending from the lowest practical orbit to well beyond geosynchronous orbit, and if a few percent of the rotating material is willing to furl and unfurl solar panels, or aim them a few degrees off from optimal, could Earth maneuver itself to some nearby safe haven, perhaps near Jupiter’s L2 point, until the white dwarf settles down? I’m skeptical folks give up on a perfectly good planet in any circumstance short of the surprise-supernova-and-breakthrough-warp-drive scenario.
If the motive for a long-lived people and its civilization is to acquire energy on a long-term basis, wouldn’t the easier and cheaper solution be:
1. Reduce the mass of the star by star-lifting to extend its lifetime, e.g from F,G,K -> M_Dwarf
2. Deploy energy collectors in a Dyson swarm to maximize the energy usage of the home star.
3. move the homeworld to maintain its biosphere, perhaps even surround it with imaging systems to simulate the original star’s output and planetary rotation to avoid tidal locking in a closer orbit that changes day and year length
It strikes me that the consumption of other stars is almost the opposite of what a benign civilization would want, especially if the implication is that their own stellar binary is a potential prey for another predatory civilization with the same motivation. This seems like an ultimate projection of our national behaviors even after the colonial period with large corporations extracting resources from other nations with the blessing and support of their domicile governments.
Your discussion reminds me of Stephen Baxter’s recent yarn “The Thousand Earths” which discusses a very long-term use of the post-white dwarf corpse of the Earth. In Baxter’s tale the Stars themselves prove to be intelligent beings who object to star-lifting attempts, so humans remake Earth’s mass into a multitude of habitats – flat Earths – in a huge dark-energy capture system to power them. The resulting “Thousand Earths” periodically get consume and reconfigured but humans can be stored in the substrate underlying them for eventual rebirth.
Baxter’s reliance on Stapledon & Matloff’s ideas is obvious, but the Dark Energy Ramjet is Baxter’s novelty which he wrote a JBIS paper about. My own thoughts are more modest – Earth can be re-engineered to survive the Sun’s Red-Giant climb and re-positioned to take advantage of the white dwarf Sun’s extended cooling phase. But those aren’t the only options.
Stephen Baxter’s Flux has microscopic people living on the surface of a neutron star.
Clarke also had plasma beings living in our sun in the short story Castaway (1947)
It would be awful if we harnessed stars destroying the habitats of any intelligent life in them without thought. [Although Clarke’s monolith builders were prepared to sacrifice the life in Jupiter for the perceived greater good of helping along the evolution of the Europans.] While I don’t expect life of intelligence to exist in stars, our knowledge of where life exists and its importance in our biosphere was, not too far in the past, very poor compared to what we know now, and likely discoveries in the future. I would hope we become more careful about what we do in the future so that we don’t destroy life through [wilful] ignorance.
Hi Alex,
Thanks for this solution (and also the idea in the other thread to transform the Moon into propellant for moving the Earth, brilliant!)
From a stellivore perspective, engaging in star-lifting kills two birds with one stone: (a) it reduces the mass of the star, indeed extending its lifetime, but it also (b) provides a huge amount of energy via accretion.
That’s where I would question your point 2. : collecting passively energy with a Dyson sphere would likely represent much less energy than the harvested energy via accretion. So it would be a huge step backwards. It also implicitly assumes that the civilization doesn’t seek to increase its energy intake for the rest of its existence.
Another argument is that in the longest term, even M_dwarfs are not eternal, and a new energy source is needed.
Of course, there could still be some highly disciplined, non-greedy civilizations that accept their local death. But if life elsewhere works as it works here, these should be rare, or easily outcompeted.
Are you actually extending the *useful* life of the low mass star by reducing its mass, or does this depend on what type of mass you are removing from it. If you are driving up its metallicity, doesn’t this exacerbate its own random flaring activity that would disrupt any organized maneuvering by the binary pair, and cause bursts of radiation that would be harmful to life in the local area?
Hi Clément,
Growth cannot continue indefinitely. For example, we can manage any rate of growth to transition to a K2 civilization. At current rates of GDP growth, we intercept all our sun’s radiation in a few thousand years. However, we cannot maintain that rate of growth transitioning into a K3 civ simply because the acquisition of the stars is limited by light speed. Growth would slow to a trickle.
If M_Dwarfs can shine for trillions of years, while not eternal [nothing is] it is a very long time. The observable stars would become increasingly red as the hotter stars died. Is there some reason to aquire more energy for the civilization? Is it per ETI energy use? Or a growing number of the ETI population? Rather than consuming energy to propel stars through teh galaxy, might it not be better to send “facilities” to other stars to extract their energy, and either expand the population in the new system, or transmit the energy back to the home star?
While the idea of stellivores is a big, bold idea, and offers an opportunity for another line of SETI research, does it make much sense from an energy usage POV?
If the civilization wwants to experience an apparent growth in energy usage, it can slow down the aging of the population so that more energy is perceived from teh POV of the time-dilated individuals. This can be done indefinitely until the the perfect heat death of the universe, or a new universe is created to restart the cycle. One of David Kipping’s “Cool Worlds” videos shows how this might work. Slowing down aging so that the universe ages more quickly around you also has the advantage of allowing greater exploration of the universe. Whilst this might only work for artificial intelligences, it might be a better trade off live that way than consuming more energy in realtime.
But I accept that we cannot know the motivations of very advanced ETI. We are just pushing the boundaries with “thought experiments”.
Alex,
Realistically speaking, to what extent do any of these fascinating scenarios (1-3) have a remote chance of ever being implemented? Several recent studies have documented the decline in the rate of “disruptive breakthroughs” in basic science. Technological progress depends to a large extent on scientific progress. Outside of the internet, online shopping, and new gadgets, truly transformative breakthroughs such as room-temperature superconductors, nanobots, nuclear fusion, radical life extension, space elevator, life-like virtual reality, and artificial general intelligence are perpetually “20 years away.”
Part of the problem is that public sector funding for basic scientific research has declined drastically in the Neoliberal era. The private sector is reticent to make high-risk investments in basic science when there is no foreseeable short-term profit; instead, there is more focus on R&D for the consumer market. This is why we have better gadgets and toys but fewer new ideas and discoveries, and creeping antibiotic resistance. I keep wondering when the sea-change breakthroughs will occur, but as I enter my mid-40s, I am starting to doubt that I will live long enough to see any of them (and there may be none period from this point onwards– see below).
When it comes to the question of technological progress and scientific progress, there are 3 main possibilities:
1. Technologically, we are nearing the limit imposed by complexity and chaos and the “low-hanging fruit” has already been picked.
2. We are nowhere near the limit of what we can achieve technologically even based on our existing understanding of natural laws.
3. We are nowhere near the limit of what we can achieve technologically even based on our existing understanding of natural laws, AND there are additional natural laws or fundamental breakthroughs in science that will allow us to go even further than we could if our current understanding of basic science has already been maximized.
Which of these possibilities, Alex, do you think is closest to reality (1-3)? And why?
@Spaceman
Do you have a reference for the decline in “disruptive breakthroughs”? What defines disruptive in that case? There have been arguments over whether basic scientifific progress has declined. I haven’t seen any reasonably definitive research on this. I would point out that in the late C18th, someone suggested that all things that could be patented had been done and no further progress could be made. How did that work out?
You are right that government funded research has declined and corporate research has increased. I think I saw recently that even corporate research in teh US had stagnated while government research funding continued to decline. On top of that, there have been suggestions that the NSF has mostly funded research where the outcome is almost known, and “blue sky” funding with high reward/risk returns (like VC funding) has declined. All bad signs – for the USA. Will other nations carry the fire instead?
Of my 3 light-hearted suggestions, I would say that energy from space is by far the most likely, and is already being planned or tested on a small scale, using technologies that have existed for decades, but are now becoming cheaper. Still relatively expensive and only suited for niche applications. But we cannot just pump and use more energy onto the Earth. The energy has to be used in space, which leads to facilities in space associated with teh energy supply – i.e. Dyson swarms. We can replace our current energy use with that from space. However, we still need to reduce mineral extraction (substitute with asteroid sources?) and then the waste problem. [It is no good getting energy and materials from space and still dumping the wastes on Earth. We need a true recycling economy, but I don’t see that happening any time soon, and it is even hard to see how it can be done in some instances.] Biological and geological processes tend not to produce anything that is not ultimately used by life. Our technologies are different and our wastes are both biologically destructive and inherently require technology to recycle them. As recycling is expensive, recycling is not done and the wastes accumulate. How long before the biosphere breaks down?
Moving the Earth and star-lifting are very remote possibilities. Moving the Earth is possible, but extremely energy and, probably, mass intensive. Star lifting? I don’t even know how it can be done.
On a brighter note, I do see a lot of progress in the life sciences. Because we want to see the practical use medically, that really slows down the introduction of the results of this science and the technology that is created. Unlike other technologies, we have to be very careful about the use of biological technologies as they can be self-replicating and impact existing life as well as our technologies. For example, there is research on finding and developing bacteria that can eat some plastics. Great, that might even solve the microplastic contamination we see everywhere from the highest mountains to the depths of the ocean. But what if those bacteria start eating the plastics that are not waste? This has been explored in SciFi, e.g. “Mutant 59:The Plastic Eaters” (1971) by Kit Pedler and Gerry Davis. Metal-eating bacteria was explored in “Beach Head” (BBC’s Out of the Unknown tv series in the 1960s based on the Clifford Simak short story, “Beachhead”).
“I leave the motivations of a machine culture spreading biological life to science fiction authors, but believe me, there’s a cool plot in there somewhere. Someone should run with it.” Have you read We Are Legion (We are bob) by Denis E Taylor? It includes elements of a machine intelligence shepherding human life and spreading us and other earth biology around the galaxy
Interesting you should mention that, Nate. A good friend has been telling me about that series. Sounds like it’s worth investigating.
I think there was also a film from 1968 involving an advanced alien species shepherding humanity through millions of years of evolution until one became a giant fetus in Earth orbit.
Then the 1982 novel and 1984 film sequels totally derailed that idea.
https://www.centauri-dreams.org/2020/07/31/the-peoples-space-odyssey-2010-the-year-we-make-contact/
The novel of the 1968 movie indicated that the ancient ones were transcendent and no longer corporeal. The movie made no suggestion of that and the director asked Carl Sagan “What would aliens look like?”, and as a result of the answer, punted. The machine left to instill the spark of higher intelligence is a transient influence only.
Therefore I think this book/movie doesn’t count as a machine civilization herding biologicals through evolution.
One might argue that Asimov’s Foundation sequels that had R. Daneel Olivaw and other robots surreptitiously guiding humanity to fill the galaxy is tangential to the concept.
Most SciFi has machine cultures warring with humanity, rather than helping it, especially in the early stages of becoming human.
Then what were those ETI doing monitoring Dave Bowman in his fancy hotel room after he traveled through their Stargate?
Those eerie noises we heard as Bowman first walked about his new home? Those were the ETI discussing Bowman as they watched him. That is a fact.
@ LJK
In the movie, the aliens were biological, hence the story about the director’s question to Sagan.
In the book, they would be immaterial, a favorite idea of Clarke’s, used several times. Minds using some property of space to exist.
IMO, neither case is ETI a machine culture.
The objects left on Earth (and on other worlds) were artifacts of ETI, not ETIs themselves. The astronaut who is transformed is of the same form as the ETIs – immaterial, able to travel in “hyperspace” with telekinesis to interact with people and terrestrial artifacts.
At least, this is my interpretation of the novel and the movie finale. Either interpretation is not machine culture nurturing our ancestors to “uplift” a biological species.
It would be better to let the sun go through its life cycle where it will kick off huge amounts of material including huge amounts of hydrogen for fusion. Later this hydrogen could be fused on the white dwarf to light the system up again. Also as the sun goes through this life cycle it’s going to get a lot brighter emitting thousands of times more energy than now before finally becoming a white dwarf. The future does indeed look very bright !
The the Earth will need to wear shades. [ boom-boom]