Centauri Dreams

Science fiction has been exploring advanced machine intelligence and its consequences for a long time now, and it’s now being bruited about in service of the Fermi paradox, which asks why we see no intelligent civilizations given the abundant opportunity seemingly offered by the cosmos. A new paper from Michael Garrett (Jodrell Bank Centre for Astrophysics/University of Manchester) explores the matter in terms of how advanced AI might provide the kind of ‘great filter’ (the term is Robin Hanson’s) that would limit the lifetime of any technological civilization.

The AI question is huge given its implications in all spheres of life, and its application to the Fermi question is inevitable. We can plug in any number of scenarios that limit a technological society’s ability to become communicative or spacefaring, and indeed there are dozens of potential answers to Fermi’s “Where are they?” But let’s explore this paper because its discussion of the nature of AI and where it leads is timely whether Fermi and SETI come into play or not.

A personal note: I use current AI chatbots every day in the form of ChatGPT and Google’s Gemini, and it may be useful to explain what I do with them. Keeping a window open to ChatGPT offers me the chance to do a quick investigation of specific terms that may be unclear to me in a scientific paper, or to put together a brief background on the history of a particular idea. What I do not do is to have AI write something for me, which is a notion that is anathema to any serious writer. Instead, I ask AI for information, then triple check it, once against another AI and then against conventional Internet research. And I find the ability to ask for a paragraph of explanation at various educational levels can help me when I’m trying to learn something utterly new from the ground up.

It’s surprising how often these sources prove to be accurate, but the odd mistake means that you have to take great caution in using them. For example, I asked Gemini a few months back how many planets had been confirmed around Proxima Centauri and was told there were none. In reality, we do have one, that being the intriguing Proxima b, which is Earth-class and in the habitable zone. And we have two candidates: Proxima c is a likely super-Earth on a five-year orbit and Proxima d is a small world (with mass a quarter that of Earth) orbiting every five days. Again, the latter two are candidates, not confirmed planets, as per the NASA Exoplanet Archive. I reported all this to Gemini and yesterday the same question produced an accurate result.

So we have to be careful about AI in even its current state. What happens as it evolves? As Garrett points out, it’s hard to come up with any area of human interest that will be untouched by the effects of AI, and commerce, healthcare, financial investigation and many other areas are already being impacted. Concerns about the workforce are in the air, as are issues of bias in algorithms, data privacy, ethical decision-making and environmental impact. So we have a lot to work with in terms of potential danger.

Image: Michael Garrett, Sir Bernard Lovell chair of Astrophysics at the University of Manchester and the Director of the Jodrell Bank Centre for Astrophysics (JBCA). Credit: University of Manchester.

Garrett’s focus is on AI’s potential as a deal-breaker for technological civilization. Now we’re entering the realm of artificial superintelligence (ASI), which was Stephen Hawking’s great concern when he argued that further developments in AI could spell the end of civilization itself. ASI refers to an independent AI that becomes capable of redesigning itself, meaning it moves into areas humans do not necessarily understand. An AI undergoing evolution and managing it at an ever increasing rate is a development that could be momentous and one that poses obvious societal risks.

The author’s assumption is that if we can produce AI and begin the process leading to ASI, then other civilizations in the galaxy could do the same. The picture that emerges is stark:

The scenario…suggests that almost all technical civilisations collapse on timescales set by their wide-spread adoption of AI. If AI-induced calamities need to occur before any civilisation achieves a multiplanetary capability, the longevity (L) of a communicating civilization as estimated by the Drake Equation suggests a value of L ∼ 100–200 years.

Which poses problems for SETI. We’re dealing with a short technological window before the inevitable disappearance of the culture we are trying to find. Assuming only a handful of technological civilizations exist in the galaxy at any particular time (and SETI always demands assumptions like this, which makes it unsettling and in some ways related more to philosophy than science), then the probability of detection is all but nil unless we move to all-sky surveys. Garrett notes that field of view is often overlooked amongst all the discussion of raw sensitivity and total bandwidth. A telling point.

But let’s pause right there. The 100-200 year ‘window’ may apply to biological civilizations, but what about the machines that may supersede them? As post-biological intelligence rockets forward in technological development, we see the possibility of system-wide and even interstellar exploration. The problem is that the activities of such a machine culture should also become apparent in our search for technosignatures, but thus far we remain frustrated. Garrett adds this:

We…note that a post-biological technical civilisation would be especially well-adapted to space exploration, with the potential to spread its presence throughout the Galaxy, even if the travel times are long and the interstellar environment harsh. Indeed, many predict that if we were to encounter extraterrestrial intelligence it would likely be in machine form. Contemporary initiatives like the Breakthrough Starshot programme are exploring technologies that would propel light-weight electronic systems toward the nearest star, Proxima Centauri. It’s conceivable that the first successful attempts to do this might be realised before the century’s close, and AI components could form an integral part of these miniature payloads. The absence of detectable signs of civilisations spanning stellar systems and entire galaxies (Kardashev Type II and Type III civilisations) further implies that such entities are either exceedingly rare or non-existent, reinforcing the notion of a “Great Filter” that halts the progress of a technical civilization within a few centuries of its emergence.

Biological civilizations, if they follow the example of our own, are likely to weaponize AI, perhaps leading to incidents that escalate to thermonuclear war. Indeed, the whole point of ASI is that in surpassing human intelligence, it will move well beyond oversight mechanisms and have consequences that are unlikely to merge with what its biological creators find acceptable. Thus the scenario of advanced machine intelligence finding the demands on energy and resources of humans more of a nuisance than an obligation. Various Terminator-like scenarios (or think Fred Saberhagen’s Berserker novels) suggest themselves as machines set about exterminating biological life.

There may come a time when, as they say in the old Westerns, it’s time to get out of Dodge. Indeed, developing a spacefaring civilization would allow humans to find alternate places to live in case the home world succumbed to the above scenarios. Redundancy is the goal, and as Garrett notes: “…the expansion into multiple widely separated locations provides a broader scope for experimenting with AI. It allows for isolated environments where the effects of advanced AI can be studied without the immediate risk of global annihilation. Different planets or outposts in space could serve as test beds for various stages of AI development, under controlled conditions.”

But we’re coming up against a hard stop here. While the advance of AI is phenomenal (and some think ASI is a matter of no more than a few decades away), the advance of space technologies moves at a comparative crawl. The imperative of becoming a technological species falls short because it runs out of time. In fact – and Garrett notes this – we may need ASI to help us figure out how to produce the system-wide infrastructure that we could use to develop this redundancy. In that case, technological civilizations may collapse on timescales related to their development of ASI.

Image: How will we use AI in furthering our interests in exploring the Solar System and beyond? Image credit: Generated by AI / Neil Sahota.

We talk about regulating AI, but how to do so is deeply problematic. Regulations won’t be easy. Consider one relatively minor current case. As reported in a CNN story, the chatbot AI ChatGPT can be tricked into bypassing blocks put into place by OpenAI (the company behind it) so that hackers can plan a variety of crimes with its help. These include money laundering and the evasion of trade sanctions. Such workarounds in the hands of dark interests are challenging at today’s level of AI, and we can see future counterparts evolving along with the advancing wave of AI experiments.

It could be said that SETI is a useful exercise partly because it forces us to examine our own values and actions, reflecting on how these might transform other worlds as beings other than ourselves face the their own dilemmas of personal and social growth. But can we assume that it’s even possible to understand, let alone model, what an alien being might consider ‘values’ or accepted modes of action? Better to think of simple survival. That’s a subject any civilization has to consider, and how it goes about doing it will determine how and whether it emerges from a transition to machine intelligence.

I think Garrett may be too pessimistic here:

We stand on the brink of exponential growth in AI’s evolution and its societal repercussions and implications. This pivotal shift is something that all biologically-based technical civilisations will encounter. Given that the pace of technological change is unparalleled in the history of science, it is probable that all technical civilisations will significantly miscalculate the profound effects that this shift will engender.

I pause at that word ‘probable,’ which is so soaked in our own outlook. As we try to establish a regulatory framework that can help AI progress in helpful ways and avoid deviations into lethality, we should consider the broader imperative. Call it insurance. I think Garrett is right in noting the lag in development in getting us off-planet, and can relate to his concern that advanced AI poses a distinct threat. All the more reason to advocate for a healthy space program as we face the AI challenge. And we should also consider that advanced AI may become the greatest boon humanity has ever seen in terms of making startling breakthroughs that can change our lives in short order.

Call me cautiously optimistic. Can AI crack interstellar propulsion? How about cancer? Such dizzying prospects should see us examining our own values and how we communicate them. For if AI might transform rather than annihilating us, we need to understand not only how to interact with it, but how to ensure that it understands what we are and where we are going.

The paper is Garrett, “Is artificial intelligence the great filter that makes advanced technical civilisations rare in the universe?” Acta Astronautica Vol. 219 (June 2024), pp. 731-735 (full text). Thanks to my old friend Antonio Tavani for the pointer.

Here’s an interesting thought. We know that at least two objects from outside our Solar System have appeared in our skies, the comet 2I/Borisov and the still enigmatic object called ‘Oumuamua. Most attention on these visitors has focused on their composition and the prospects of one day visiting such an interloper, for it is assumed that with new technologies like the Vera Rubin Observatory and its Legacy Survey of Space and Time (LSST), we will be picking up more of the same.

But consider origins. Extrapolating backward to figure out where either object came from quickly exhausts the most patient researcher, for it only takes the slightest changes in trajectory to widen the search field so broadly as to be useless. That’s especially true since we don’t know the ages of the objects, which may span hundreds of millions of years.

Enter Cole Gregg (University of Western Ontario), who has embarked on a project to study the question from a different perspective. Gregg asks how likely it is that material from another star could be passing through Sol’s neighborhood. As presented at the American Astronomical Society’s Division for Planetary Sciences meeting in Boise, Idaho earlier this month, his calculations explore the gravitational interactions such objects would experience. And he studies whether ‘streams’ of such material could identify by their common characteristics the likely system of origin.

The question is intriguing given how difficult it is to get a probe to Alpha Centauri at present levels of technology. Material from that system, if identified as such, would have interesting implications, especially with regard to the dispersal of chemical elements and organic molecules. The idea of panspermia rides on the possibility that life itself might move between planets and even stars in such material, so getting our hands on something from another star would offer obvious benefits.

Gregg is working on this project with colleague Paul Wiegert, who is perhaps best known for pioneering work with Matt Holman back in the 1990s on planetary orbits possible in the Alpha Centauri system. That work established that rocky terrestrial worlds could remain on stable orbits around Centauri A or B within 3 AU of the host stars, and a bit further out if the planetary orbit was retrograde. As these orbits were stable for billions of years, this finding was an incentive for deeper investigation into Alpha Centauri as a possible home for life.

Gregg and Wiegert now turn their attention to what they call ‘interstellar meteor streams,’ analyzing the development of such streams as they form and “as the material evolves in time through a time-independent, asymmetric potential model for our galaxy.” Their method is to conduct simulations with existing galactic models that involve ejected material in the galactic bulge, the halo and the disk, with the direction of ejection oriented randomly and at speeds of up to 15 kilometers per second.

We’re early in the process here (remember that this work has just been presented), but quoting from a brief write-up made available for a 2023 conference:

As expected, since the physics of their motion is identical, we see the ejecta travel through the disk of the Galaxy in much the same way that stars do. However, through the progression of the simulation we see complicated and interesting effects on the ejecta swarm, hinting at the complicated evolution of interstellar meteoroid streams. This talk will also discuss the implications of the modeled motion on the identification of interstellar meteoroid streams.

For stars in the galactic disk (which is where we are), material ejected from their systems evolves in a way similar to meteoroid streams we see in the Solar System, undergoing ‘orbital shear’. These streams can be long-lived and may include a flux of material passing through our Solar System that, while small, would be of great interest. Gregg sees his ongoing work as refining the process of interstellar transfer and producing population estimates for interstellar visitors currently nearby.

Image: A hypothetical interstellar meteoroid stream after 185 Myr of evolution from a burst ejection originating in the Alpha Centauri system. Credit: Cole Gregg.

As to the Centauri system, Gregg told Sky & Telescope in an article published this month that his calculations using a simplified model of the Milky Way show that about 0.03 percent of material ejected from Alpha Centauri could reach the Solar System, and perhaps most important, be recognized as coming from that source. We’re talking about material that could be as small as dust grains and as large as a comet or asteroid, but moving within a stream that has similar orbital velocities within the galaxy and similar positions, the latter traits making their source identifiable.

Gregg’s work is intriguing and also preliminary, for he intends to produce a full follow-up study looking to refine the galactic model and include better estimates on the likely size of the material that would have made such a crossing. So at this point what we have is only a possibility that may be excluded if the further analysis rules it out. But it’s a worthwhile study given the implications of finding such a stream.

The Sky & Telescope article is from October 18, 2024, titled “Are Objects from Alpha Centauri Streaming by Earth?” (available here). Gregg’s writeup for a 2023 conference is “The Development of Interstellar Meteoroid Streams” (full text). A PowerPoint presentation can be found here. The Wiegert and Holman paper, a key paper in Alpha Centauri studies, is “The Stability of Planets in the Alpha Centauri System,” Astronomical Journal 113 (1997), 1445–1450 (abstract).

Given our decades-long lack of success in finding hard evidence for an extraterrestrial civilization, it hardly comes as a surprise that a recent campaign studying the seven-planet TRAPPIST-1 system came up without a detection. 28 hours of scanning with the Allen Telescope Array by scientists at the SETI Institute and Penn State University produced about 11,000 candidate signals for further analysis, subsequently narrowed down to 2,264 of higher interest. None proved to be evidence for non-human intelligence, but the campaign is interesting in its own right. Let’s dig into it.

The unique configuration of the TRAPPIST-1 planets allowed the scientists involved to use planet-planet occultations (PPOs). A cool M-dwarf star, TRAPPIST-1 brings with it the features that make such stars optimal for detecting exoplanets. The relative mass and size of the planets and star mean that if we’re looking for rocky terrestrial-class worlds, we’re more likely to find and characterize them than around other kinds of star. True, they’re also orbiting a class of star that is dim, but another beauty of TRAPPIST-1 is that it’s only 40 light years out, and we see its seven planets virtually edge-on.

Planets e, f and g can be squeezed into the star’s habitable zone (liquid water on the surface) if we tweak our numbers for possible atmospheres. The edge-on vantage means that planets can pass in front of each other from our viewpoint, with the additional advantage that this well-studied system has planetary orbits that are sharply defined. This raises intriguing possibilities when you consider our own space activities. The Deep Space Network sends powerful signals to communicate with distant craft like the Voyagers, signals wide enough to propagate beyond them and into deep space. The right kind of receiver, if by chance aligned with them, might make a detection, producing evidence for a technology by the nature of its signal.

At TRAPPIST-1, there are seven planet-planet occultations, with two of them involving a potential transmission-source planet within the star’s habitable zone. But we have to consider that transmissions between planets might not be this limited, for radio traffic could move through relays placed for communications purposes on worlds that are uninhabitable. This would obviously be traffic never intended for interstellar reception, the kind of ongoing activity that marks a society communicating with itself, but perhaps leaving a technosignature that would reach the Earth through the width of its beam.

Image: A look from above at the communications line of sight between two worlds in the TRAPPIST-1 system, illustrating the PPO method used in this study. Credit: SETI Institute/Zayna Sheikh.

The possibilities of a detection using this PPO technique vary, of course, with the orbital parameters of the planets in any given system. We must also account for the drift rates produced by orbital motion. The paper explains the recent search’s technique this way:

…it is assumed that the TRAPPIST-1 planets are tidally locked due to their proximity to their host star and will have a negligible rotational contribution to the drift rate of a transmitter on their surfaces. Additionally, their orbital parameters are well constrained, making it possible to calculate the drift rate contributions from their orbital motion. Satellite transmitters in circular orbit around each planet could produce much higher drift rates, up to an additional ∼45 nHz on top of the contribution from the planet’s orbit around the star. However, we have chosen to limit our scope to analogues of our deep space communications, the strongest of which are surface transmitters to deep space probes.

The seven planet-planet occultations studied during the 28 hours of observation ranged from 8.6 minutes to 99.4 minutes. And it turns out that widening that window of observation through simulations produces numerous PPOs with a similarly large range of duration, making this strategy still more interesting. The animation below shows the TRAPPIST-1 system in motion and the possible communications opportunities. Credit: Tusay et al., citation below.

Animation: This is Figure 10 from the paper, the caption of which reads: Simulated potential PPO events during our observations. Online viewers will see a concatenated video of the orbital configuration of the system during each of the observations, including any potential PPO events that we found to occur during those windows. A still image of a PPO event during the observation on Oct 29, 2022 is included where the animation is not accessible. The top panel shows a bird’s-eye view of the system with planet radii scaled up for better viewing. The distances and beam sizes are to scale, assuming a beam created with a 3.4m dish at 3.3 GHz (the maximum frequency observed during this particular session) from the surface of planet g aimed at planet e. The bottom panel shows the edge-on view with planet sizes scaled with distance, showing how much of the beam spills over the planet toward the direction of Earth in the negative z-direction. The red dashed lines in the illustrated beam is the inner angle blocked by the occulting planet, e. The blue dashed lines show the outer angle of the beam that would spill over the planet. The window for this event lasted roughly 95 minutes. Credit: Tusay et al.

Is this method the longest of longshots? SETI itself might be described that way, depending on your views of life in the cosmos. But our steadily growing capabilities at signal detection can’t be ruled out when we consider the possibilities. From the paper:

The analysis of the observations presented here demonstrates that precise characterization of ideal systems, like TRAPPIST-1, enabling orbital dynamical modeling and prediction of PPO events offer practical application for leaked emission searches. This provides SETI a powerful new observational tool and search strategy. As signal detection and RFI mitigation pipelines improve, the inclusion of PPOs to provide narrow search windows may make it more feasible to increase time resolution and sensitivity at higher drift rates.

What beckons most strongly about technosignatures is that they assume no intent (which in any case would be unguessable) on the part of a hypothetical alien civilization. We would essentially be eavesdropping on their activities. Grad student Nick Tusay (Pennsylvania State), lead author of the paper on this work, adds this: “[W]ith better equipment, like the upcoming Square Kilometer Array (SKA), we might soon be able to detect signals from an alien civilization communicating with its spacecraft.” And that would be a SETI detection for the ages.

The paper is Tusay et al., “A Radio Technosignature Search of TRAPPIST-1 with the Allen Telescope Array,” currently available as a preprint.