Risk Mitigation for Advanced Civilizations

Alastair Reynolds’ 2008 novel House of Suns contains what must be the most outrageous solution for an endangered civilization I’ve ever encountered. Set some 6 million years in the future, the story involves technologies at the Kardashev Type III level — in other words, civilizations that are capable of harnessing the energy of entire galaxies. At one point, a supermassive star whose pending death threatens a local civilization is enclosed in an enormous ‘stardam,’ made out of remnant ‘ringworlds’ from a long-lost culture that litter the galaxy.

I believe we’re normally considered to be at about Kardashev level 0.7, so a feat like this is utterly the stuff of science fiction, but in Reynolds’ hands it makes for a robust tale. Here’s how future humans discuss it in the novel:

To dam a star, to enclose it completely, would require the construction of a Dyson shell. Humans can shroud a star with a swarm of bodies, a Dyson cloud, but we cannot forge a sphere. Instead we approximate one by surrounding a star with thousands of ringworlds, all of similar size but with no two having exactly the same diameter. We make a discus and then start tilting, until each ringworld is encircling the star at a unique angle. The light of the star rams through the narrowing gaps as the ringworlds tighten into their final orientation. Shutters close on a fierce, deadly lantern.

And there you are — what would have been death by supernova becomes averted as the energies of the dying star bounce back and forth between these myriad reflecting surfaces until over aeons, they gradually leak out as infrared. If this seems surreal, the novel even trumps the stardam with a star (in the Andromeda galaxy) completely enclosed in a representation of the Platonic Solids. To learn how this came about, I send you to Reynolds, for whom I’ve developed great admiration in the last five or six years. This is an author whose concepts are big enough to call up Olaf Stapledon and Star Maker (1937).

The Threat from Exploding Stars

I was delighted to see that Milan Ćirković, whose work we’ve looked at frequently in these pages, mentions House of Suns in his new paper, slated to appear in Acta Astronautica. Ćirković (Astronomical Observatory, Belgrade) has been a key player in the definition and exploration of so-called Dysonian SETI, which involves moving beyond radio and optical wavelengths to consider the possible signature that a truly advanced civilization might leave through its activities, which do not necessarily involve communication.

We looked last summer at the possibility of ‘stellified’ objects, in a Ćirković paper that considered the manipulation of a gas giant or even a brown dwarf to extract energy, and the SETI observables this might create (see SETI: Detecting ‘Stellified’ Objects, or Rethinking SETI’s Targets). The new work, written with Branislav Vukotić (University of Oxford) looks at the response by an advanced civilization to threats from supernovae and gamma ray bursts (GRBs), with the nod toward the Reynolds novel coming in as an extreme response by what the paper refers to as humanity++, a civilization capable of interstellar flight and engineering at the interstellar level. This is a culture that may be biological or not, but it is one capable of changing its environment at large scales of space, time and energy.

Image: On January 21, 2014, astronomers witnessed a supernova soon after it exploded in the Messier 82, or M82, galaxy. Telescopes across the globe and in space turned their attention to study this newly exploded star, including Chandra. Astronomers determined that this supernova, dubbed SN 2014J, belongs to a class of explosions called “Type Ia” supernovas. These supernovas are used as cosmic distance-markers and played a key role in the discovery of the Universe’s accelerated expansion, which has been attributed to the effects of dark energy. Scientists think that all Type Ia supernovas involve the detonation of a white dwarf. One important question is whether the fuse on the explosion is lit when the white dwarf pulls too much material from a companion star like the Sun, or when two white dwarf stars merge. Credit: NASA/CXC/SAO/R.Margutti et al.

All of this makes for fascinating speculation on the SETI level, and I intend to get to that in a subsequent article, but the bulk of the new Ćirković paper deals with the far-future scenario by way of contrasting it with a culture not terribly more advanced than our own. The author dubs it humanity+, a civilization perhaps of the Kardashev 1 level or a bit beyond, that is capable of using the resources of the Solar System for industrial purposes, asteroid mitigation, exploration and colonization. This is a culture we could, barring various forms of intervening catastrophe, imagine emerging on and from our planet within centuries.

The question becomes, would a culture that had the means to do it protect itself against existential risk in the form of supernovae and GRBs? We’re currently just learning about what we can do to respond to the threat of impacts on Earth, by studying asteroids and comets to learn how we might alter a dangerous trajectory. We’re also learning about hazards like supervolcanoes, and the ways in which such activity has altered our planet in the past.

Supernovae and gamma ray bursts present what seems to be an entirely different kind of threat, and one that seems to play out on a galactic timescale. GRBs have been considered by some authors as offering a regulation mechanism preventing the spread of life in the distant past of the Milky Way, and it’s interesting that cosmic explosion rates have generally been declining over cosmic time, as shown in cosmological observations and models of star formation. I am not aware of any previous risk analysis on GRBs or supernovae of the sort that Ćirković and Vukotić undertake here, but the paper explains why this is understandable.

While we already have an extensive literature on impact prediction and mitigation, one reason for our attention is the existence of recent evidence, such as the 2013 Chelyabinsk air burst and the 1908 explosion that levelled thousands of acres in Siberia, not to mention our growing understanding of the Late Heavy Bombardment’s effects on the primordial Earth.

Likewise, supervolcanism has been little studied until recently, but while its effects may litter our past, we can also relate it to catastrophic eruptions in our own era, like Krakatoa in 1883 or Mount Tambora in 1815. Supernovae and GRBs are hardly as visible, but we do have reason to believe they can have disastrous effects on a nearby biosphere, and some researchers have argued for certain extinctions in Earth’s history to be the result of nearby cosmic explosions.

Will the threat of such catastrophes drive a future civilization to study mitigation efforts to prevent the worst of their effects? We have to consider the question in long timescales indeed:

…it is reasonable to assume – Earth’s single case notwithstanding – that evolving intelligent beings, not to mention technological civilizations, requires timescales on the order of several Gyr, during which a single close explosion could cut or derail the evolutionary chain of events leading to that outcome, this indicates that once a civilization emerges, it is only rational to seriously consider risk from such events and possibilities of its mitigation.

The paper goes on to refer to simulations reported within its pages by author Vukotić:

While the resolution of the simulation of Vukotić et al. is still insufficient for conclusions about number of individual stars and planetary systems, it is still indicative and motivating for further work in the area. For the present purposes, we note that no part of any spiral galaxy can be considered safe from cosmic explosions in the long run. And as the timeframe considered by an intelligent species grows longer, more relevant becomes the issue of mitigation. It is reasonable to hope that near-future simulations of habitability will offer more complete and precise account of the amount of risk faced by different parts of the Galactic Habitable Zone.

Image: GRB 111209A exploded on Dec. 9, 2011. The blast produced high-energy emission for an astonishing seven hours, earning a record as the longest-duration GRB ever observed. This false-color image shows the event as captured by the X-ray Telescope aboard NASA’s Swift satellite. Credits: NASA/Swift/B. Gendre (ASDC/INAF-OAR/ARTEMIS).

Timing the Event

Mitigation of the damage from a cosmic explosion would seem to be an impossibility, given our lack of knowledge of when one is going to occur. We would need to know not just where the explosion was centered but how strong it would be, and as the paper points out, how isotropic in terms of its emissions. We’re a long way in terms of supernovae, not to mention GRBs, from being able to work out timeframes for the explosion of even nearby stars like eta Carinae. Our present-day technology could do nothing to reduce the effects of a cosmic explosion, but Ćirković and Vukotić, remember, are speculating about a future humanity.

This is a civilization moving past Kardashev Level I that has learned a great deal more than we know about supernovae and GRBs, and the authors see no reason in principle why explosion times, energies, spectra, cosmic-ray acceleration power and other factors for these phenomena will not eventually be much better understood. Prediction is an essential, and while we are well on the way toward predicting dangerous asteroid encounters, we have much to do before we reach the level of understanding that GRB mitigation would involve.

While prediction of weather in its local detail is still notoriously uncertain, the trajectory and timing of hurricanes, cyclones and other storm systems storms is today routinely predicted, often enough in advance for efficient mitigation measures to be deployed. History of science offers many examples of the increase of reliability and accuracy of predictions in various other areas, from eclipses to neutrino pulse from supernova SN 1987 A. Even in the areas where predictions have not built a good track record so far (e.g., earthquakes, volcanic eruptions, economic crises), we are gradually focusing on the main obstacles to further progress and the development of massive numerical simulations did much to understand the related problems much better.

If such prediction could be mastered, then we or some hypothetical extraterrestrial civilization could investigate how to protect our planet or entire planetary system from the effects of a cosmic explosion. What kind of technologies would this most likely involve, and what kind of signature might it leave in our astronomical data? We’ll look at the possibilities tomorrow.

Centauri Dreams’ take: Learning how to predict events like these may be well beyond our understanding, but it is not unreasonable to think that a sufficiently advanced civilization may have found ways to assess their likelihood. Dysonian SETI looks at technologies, Dyson swarms being a classic example, that do not contradict physical law but are beyond conceivable human engineering. It makes sense to consider possible signatures of advanced civilizations even though we are ourselves unable to duplicate them. Thus I agree with Ćirković and Vukotić on this point from their paper:

It is important to emphasize from the outset that while details of the interaction of cosmic explosions with biospheres are still largely unknown, they are of minor importance for the central goal of this paper. As Ludwig Boltzmann [71] famously said: “It may be objected that the above is nothing more than a series of imperfectly proved hypotheses. But granting its improbability, it suffices that this explanation is not impossible. For then I have shown that the problem is not insoluble, and nature will have found a better solution than mine.” [present authors’ emphasis] We would add only that “nature” here should be expanded to encompass actions of advanced technological civilizations – which may or may not be recognizable as such.

The paper is Ćirković and Vukotić, “Long-term prospects: Mitigation of supernova and gamma-ray burst threat to intelligent beings,” accepted at Acta Astronautica. See also Vukotić et al., “‘Grandeur in this view of life'”: N-body simulation models of the Galactic habitable zone,” Monthly Notices of the Royal Astronomical Society published online 12 April 2016 (abstract / preprint).