Centauri Dreams

My friend Frank Taylor was in town over the Thanksgiving holiday, having flown in from South Africa. With his wife Karen, Frank has spent the years since 2009 circumnavigating the globe aboard a 50-foot catamaran called Tahina, an adventure chronicled with spectacular photography on the Tahina Expedition blog. I highly recommend the site for anyone interested in travel and the sea, not to mention how high tech has transformed the ancient art of sailing. But when we spoke recently just before Frank returned to Africa, he had another kind of high tech in mind. Specifically, what had I thought about the film Interstellar?

I haven’t delayed my comments on the movie intentionally, but I was slow in getting to see it, missing the opportunity at the end of the Tennessee Valley Interstellar Workshop and then getting involved in recent activities including the One Earth New Horizons Message workshop at Stanford. I also wanted to read Kip Thorne’s The Science of Interstellar (Norton, 2014) and give the movie a second viewing. All that behind me, it’s time to explain why I was surprised by Interstellar. My expectations for Hollywood science fiction are always low, as I’ve found that today’s filmmaking wizardry all too often masks serious flaws in plot and character.

I can find problems in Interstellar as well, as many reviewers have, but I think this is an important movie whose mistakes aren’t significant compared to what it accomplishes. Interstellar is a movie that will baffle a large part of its audience, the movie-going public far more comfortable with battles in space and sleek starships like the Enterprise. This is not an audience that will easily follow the twists and turns through time and space that Christopher Nolan has created. But Nolan’s attention to detail, his partnership with Thorne, and his insistence on scientific plausibility wherever possible will get through to an important subset.

I’m talking about younger people with an interest in science for whom the movie’s stunning visuals will impel them to learn how to untangle the plot. For the intellectually curious, Interstellar is a tandem creation, a movie/book duality where each plays off the other — the motivated minority will want to immerse themselves in both. The film’s plot is demanding and operates at various degrees of believability, but there is a science puzzle to be untangled here, one to which Thorne’s book offers the key. When I was researching Centauri Dreams back in 2002-2004, I was surprised at how many scientists and aerospace engineers told me they had chosen their fields because of science fiction novels like Poul Anderson’s Tau Zero. This movie will have the same effect. In fact, I can think of no movie that is so likely to create careers in the sciences, particularly physics, than this one.

Let’s talk about why. Here I get into details and suppose I should say that there may be spoilers below for those who haven’t yet seen Interstellar, so proceed with caution. I could focus on various issues, from a worldwide blight to passage through a wormhole, but the film’s treatment of black holes is what I’ll use as my working material. The wormhole itself, out near Saturn’s orbit and an apparent way out for a desperate humanity, is richly described in Thorne’s chapters, especially with regard to the special effects that bring it to life.

Our protagonist, Cooper, must learn which of three planets in an unusual system dominated by an enormous black hole called Gargantua is most suited for humans. When he and his team need to get to one of these, Miller’s Planet, from their parking orbit near the black hole, they have to produce huge velocity changes in the range of 100,000 kilometers per second. Thorne goes through the physics of this, including the bizarre time distortion on a world so close to a black hole. The upshot is that a gravitational slingshot maneuver must be performed. The movie skims over the matter quickly, but Cooper does discuss how this must have been done later, when he talks about using a neutron star to decelerate. The neutron star is a bit of a fudge — it turns out it wouldn’t be big enough to force the needed maneuver, but an intermediate-mass black hole would do the trick. Thorne made this case to Nolan but the director stuck with the neutron star.

That’s a scientific error forced by Hollywood values. Thorne relates his objections to Nolan during the re-writing of the screenplay and goes on to explain what happened:

…he [Nolan] didn’t want to confuse his mass audience by having more than one black hole in the movie. One black hole, one wormhole, and also a neutron star, along with Interstellar‘s other rich science, all to be absorbed in a fast-paced two hour film; that was all Chris thought he could get away with. Recognizing that strong gravitational slingshots are needed to navigate near Gargantua, Chris included one slingshot in Cooper’s dialog, at the price of using a scientifically implausible deflector: the neutron star instead of a black hole.

Interstellar is closer to three hours than two (Thorne was writing before the film was finalized), but does anything else about this bother you? I’m going to argue that the combination of Nolan’s movie and Thorne’s book — and the fruitful collaboration the two engaged in throughout — induces the kind of puzzle-solving ethos that will prompt many a young mind to dig deeper into the movie’s physics. Nolan made a choice with a mass audience in mind, but the framework of that choice is laid bare in Thorne’s book, which goes on to explain how careful Nolan was to stick to scientific plausibility where he felt that he could. Filmmaking is always a matter of compromise, but Nolan was surprisingly tough. Finding where Interstellar works and where it stretches science out of shape is itself a lesson in problem solving.

The point is, the director was thinking about these things within a framework that, in terms of its spectacular visuals, is meticulous about getting the larger details right. Think about the accretion disk around the black hole Gargantua. Here we’re seeing a magnetic field in the process of converting gravitational energy into heat and then light — the field, explains Thorne, provides the friction that slows the circumferential motion of gas in the disk even as the black hole’s gravity tries to speed up the infalling material, with kinetic energy being converted into heat and light along the way. But go to the projections of black hole accretion disks you’ll find on the Net or in technical publications and you’ll find Nolan’s depiction is far more spectacular. Another Hollywood-enforced choice?

No. What Nolan and Thorne added was the gravitational lensing of the disk by its own black hole, an effect explored through computer code developed for the film. While you would expect that portion of the disk behind the black hole to be out of sight, gravitational lensing produces two images of it, one above and the other below Gargantua. This is special effects wizard Eugénie van Tunzelmann’s work, carefully wrought to produce the nested effect Thorne describes:

Inside these primary images, we see thin secondary images of the disk, wrapping over and under the shadow, near the shadow’s edge. And if the picture were made much larger, you would see tertiary and higher-order images, closer and closer to the shadow.

Moreover, Gargantua’s distortion of spacetime distorts the disk images, pushing the perceived disk away from the shadow on one side and toward the shadow on the other, creating an effect that appears lopsided. Here again Nolan intervened in an attempt to avoid confusion, especially as the audience tried to work out the reason for the lopsidedness of the disk and the star patterns created near its edge. So for the purposes of the imagery, he slowed the spin of Gargantua to reduce the effect, just as van Tunzelmann removed the Doppler shift created by the disk’s motion, which would have created an even more lopsided and confusing effect.

What pleases me here is that these changes and their rationale are thoroughly explored in Kip Thorne’s book, which likewise offers those intrigued with such visualizations the opportunity to explore how they could be fine-tuned and rendered with greater accuracy. Given the Hollywood culture in which he operates, I think that Christopher Nolan produced a movie with as much scientific accuracy as he could get past his producers, given the imperative for ratings and box office sales.

Most people are going to be wowed by the visuals; some will be dismayed by the all but supernatural intervention of beings from a higher dimension who may be our descendants. But a few, the ones I’m focused on, are going to use the high points of this movie — its unapologetic call for exploration, its entanglement with science as a form of quest — to choose to learn more, and there is no more engaging a guide than Kip Thorne to show them the way. Thorne says he was moved by the underlying message of Interstellar that the universe can be viewed optimistically because our species is capable of choosing its future:

But doing so, controlling our own fate, requires that a large fraction of us understand and appreciate science: How it operates. What it teaches us about the universe, the Earth, and life. What it can achieve. What its limitations are, due to inadequate knowledge or technology. How those limitations may be overcome. How we transition from speculation to educated guess to truth. How extremely rare are revolutions in which our perceived truth changes, yet how very important.

Thirty years from now there will be working scientists who explain to interviewers how Interstellar, a movie flawed by occasional mawkishness (think of Amelia Brand’s regrettable lines about love being the fifth dimension), weighed down by what may be the ultimate deus ex machina (in the form of Cooper operating through the tesseract), and reactive to Hollywood’s relentless popular ethos, nonetheless captured their imagination so that they read a book (Thorne’s) that helped to launch them down a path whose end they could not imagine. I call that a fine result, and reiterate my surprise in finding a Hollywood blockbuster I can seriously recommend.

What trajectory will our civilization follow as we move beyond our first tentative steps into space? Nick Nielsen returns to Centauri Dreams with thoughts on multi-generational projects and their roots in the fundamental worldview of their time. As the inspiring monuments of the European Middle Ages attest, a civilizational imperative can express itself through the grandest of symbols. Perhaps our culture is building toward travel to the stars as the greatest expression of its own values and capabilities. Is the starship the ultimate monument of a technological civilization? In addition to continuing work in his blogs Grand Strategy: The View from Oregon and Grand Strategy Annex, Nielsen heads Project Astrolabe for Icarus Interstellar, described within the essay.

by J. N. Nielsen

If interstellar flight proves to be possible, it will be possible only in the context of what Heath Rezabek has called an Interstellar Earth: civilization developed on Earth to the degree that it is capable of launching an interstellar initiative. This is Earth, our familiar home, transformed into Earth, sub specie universalis, beginning to integrate its indigenous, terrestrial civilization into its cosmological context.

Already life on Earth is thoroughly integral with its cosmological context, in so far as astrobiology has demonstrated to us that the origins and processes of life on Earth cannot be fully understood in isolation from the Earth’s cosmic situation. The orbit, tilt, and wobble of the Earth as it circles the sun (Milankovitch cycles), the other bodies of the solar system that gravitationally interact with (and sometimes collide with) Earth, the life cycle of the sun and its changing energy output (faint young sun problem), the position of our solar system with the galactic habitable zone (GHZ), and even the solar system bobbing up and down through the galactic plane, subjecting Earth to a greater likelihood of collisions every 62 million years or so (galactic drift) – all have contributed to shaping the unique, contingent history of terrestrial life.

What other distant unknowns shape the conditions of life here on Earth? We cannot yet say, but there may be strong bounds on the earliest development of complex life in the universe, other than the age of the universe itself. For example, recent research on gamma ray bursts suggests that the universe may be periodically sterilized of complex life, as argued in the paper On the role of GRBs on life extinction in the Universe by Tsvi Piran and Raul Jimenez (and cf. my comments on this), which was also the occasion of an article in The Economist, Bolts from the blue. Intelligent life throughout the universe may not be much older than intelligent life on Earth. This argument has been made many times prior to the recent work on gamma ray bursts, and as many times confuted. A full answer must await our exploration of the universe, but we can begin by narrowing the temporal boundaries of possible intelligence and civilization.

Image: Lodovico Cardi, also known as Cigoli, drawing of Brunelleschi’s Santa Maria del Fiore, 1613.

From the perspective of natural history, there is no reason that cognitively modern human-level intelligence might not have arisen on Earth a million years earlier than it did, or even ten million years earlier than it did. On the other hand, from the same perspective there is no reason that such intelligence might not have emerged for another million years, or even another ten million years, from now. Once biology becomes sufficiently complex, and brains supervening upon a limbic system become sufficiently complex, the particular time in history at which peer intelligence emerges is indifferent on scientific time scales, though from a human perspective a million years or ten million years makes an enormous difference. [1]

Once intelligence arose, again, it is arguably indifferent in terms of natural history when civilization emerges from intelligence; but for purely contingent factors, civilization might have arisen fifty thousand years earlier or fifty thousand years later. Hominids in one form or another have been walking the Earth for about five million years (even if cognitive modernity only dates to about 60 or 70 thousand years ago), so we know that hominids are compatible with stagnation measured on geological time scales. Nevertheless, the unique, contingent history of terrestrial life eventually did, in turn, give rise to the unique, contingent history of terrestrial civilization, the product of Earth-originating intelligence.

The sheer contingency of the world makes no concessions to the human mind or the needs of the human heart. Blaise Pascal was haunted by this contingency, which seems to annihilate the human sense of time: “When I consider the short duration of my life, swallowed up in the eternity before and after, the little space which I fill and even can see, engulfed in the infinite immensity of spaces of which I am ignorant and which know me not, I am frightened and am astonished at being here rather than there; for there is no reason why here rather than there, why now rather than then.” [2]

Given the inexorable role of contingency in the origins of Earth-originating intelligence and civilization, we might observe once again that, from the perspective of the natural history of civilization, it makes little difference whether the extraterrestrialization of humanity as a spacefaring species occurs at our present stage of development, or ten thousand years from now, or a hundred thousand years from now. [3] When civilization eventually does, however, follow the example of the life that preceded it, and integrates itself into the cosmological context from which it descended, it will be subject to a whole new order of contingencies and selection pressures that will shape spacefaring civilization on an order of magnitude beyond terrestrial civilization.

The transition to spacefaring civilization is no more inevitable than the emergence of intelligence capable of producing civilization, or indeed the emergence of life itself. If it should come to pass that terrestrial civilization transcends its terrestrial origins, it will be because that civilization seizes upon an imperative informing the entire trajectory of civilization that is integral with a vision of life in the cosmos – an astrobiological vision, as it were. We cannot know the precise form such a civilizational imperative might take. In an earlier Centauri Dreams post, I discussed cosmic loneliness as a motivation to reach out to the stars. This suggests a Weltanschauung of human longing and an awareness of ourselves as being isolated in the cosmos. But if we were to receive a SETI signal next week revealing to us a galactic civilization, our motivation to reach out to the stars may well take on a different form having nothing to do with our cosmic isolation.

At the first 100YSS symposium in 2011, I spoke on “The Moral Imperative of Human Spaceflight.” I realize now I might have made a distinction between moral imperatives and civilizational imperatives: a moral imperative might or might not be recognized by a civilization, and a civilizational imperative might be moral, amoral, or immoral. What are the imperatives of a civilization? By what great projects does a civilization stand or fall, and leave its legacy? With what trajectory of history does a civilization identify itself and, through its agency, become an integral part of this history? And, specifically in regard to the extraterrestrialization of humanity and a spacefaring civilization, what kind of a civilization would not only recognize this imperative, but would center itself on and integrate itself with an interstellar imperative?

Also at the first 100YSS symposium in 2011 there was repeated discussion of multi-generational projects and the comparison of interstellar flight to the building of cathedrals. [4] In this analogy, it should be noted that cathedrals were among the chief multi-generational projects and are counted as one of the central symbols of the European middle ages, a central period of agrarian-ecclesiastical civilization. For the analogy to be accurate, the building of starships would need to be among the central symbols of an age of interstellar flight, taking place in a central period of mature industrial-technological civilization capable of producing starships.

To take a particular example, the Duomo of Florence was begun in 1296 and completed structurally in 1436—after 140 years of building. When the structure was started, there was no known way to build the planned dome. (To construct the dome in the conventional manner would have required more timber than was available at that time.) The project went forward nevertheless. This would be roughly equivalent to building the shell of a starship and holding a competition for building the propulsion system 122 years after the project started. The dome itself required 16 years to construct according to Brunelleschi’s innovative double-shelled design of interlocking brickwork, which did not require scaffolding, the design being able to hold up its own weight as it progressed. [5]

It is astonishing that our ancestors, whose lives were so much shorter than ours, were able to undertake such a grand project with confidence, but this was possible given the civilizational context of the undertaking. The central imperative for agrarian-ecclesiastical civilization was to preserve unchanged a social order believed to reflect on Earth the eternal order of the cosmos, and, to this end, to erect monuments symbolic of this eternal order and to suppress any revolutionary change that would threaten this order. (A presumptively eternal order vulnerable to temporal mutability betrays its mundane origin.) And yet, in its maturity, agrarian-ecclesiastical civilization was shaken by a series of transformative revolutions—scientific, political, and industrial—that utterly swept aside the order agrarian-ecclesiastical civilization sought to preserve at any cost. [6]

The central imperative of industrial-technological civilization is the propagation of the STEM cycle, the feedback loop of science producing technologies engineered into industries that produce better instruments for science, which then in turn further scientific discovery (which, almost as an afterthought, produces economic growth and rising standards of living). [7] One cannot help but wonder if this central imperative of industrial-technological civilization will ultimately go the way agrarian-ecclesiastical civilization, fostering the very conditions it seeks to hold in abeyance. In any case, it is likely that this imperative of industrial-technological civilization is even less understood than the elites of agrarian-ecclesiastical civilization understood the imperative to suppress change in order to retain unchanged its relation to the eternal.

It may yet come about that the building of an interstellar civilization becomes a central multi-generational project of industrial-technological civilization, as it comes into its full maturity, as a project of this magnitude and ambition would be required in order to sustain the STEM cycle over long-term historical time (what Fernand Braudel called la longue durée). We must recall that industrial-technological civilization is very young—only about two hundred years old—so that it is still far short of maturity, and the greater part of its development is still to come. Agrarian-ecclesiastical civilization was in no position to raise majestic gothic cathedrals for its first several hundred years of existence. Indeed, the early middle ages, a time of great instability, are notable for their lack of surviving architectural monuments. The Florence Duomo was not started until this civilization was several hundred years old, having attained a kind of maturity.

The STEM cycle draws its inspiration from the great scientific, technical, and engineering challenges of industrial-technological civilization. A short list of the great engineering problems of our time might include hypersonic flight, nuclear fusion, and machine consciousness. [8] The recent crash of Virgin Galactic’s SpaceShipTwo demonstrates the ongoing difficulty of mastering hypersonic atmospheric flight. We can say that we have mastered supersonic atmospheric flights, as military jets fly every day and only rarely crash, and we can dependably reach escape velocity with chemical rockets, but building a true spacecraft (both HOTOL and SSTO) requires mastering hypersonic atmospheric flight, as well as making the transition to exoatmospheric flight) and this continues to be a demanding engineering challenge.

Similarly, nuclear fusion power generation has proved to be a more difficult challenge than initially anticipated. I recently wrote in One Hundred Years of Fusion that by the time we have mastered nuclear fusion as a power source, we will have been working on fusion for a hundred years at least, making fusion power perhaps the first truly multi-generational engineering challenge of industrial-technological civilization—our very own Florentine Duomo, as it were.

With machine consciousness, if we are honest we will admit that we do not even know where to begin. AI is the more tractable problem, and the challenge that attracts research interest and investment dollars, and increasingly sophisticated AI is likely to be an integral feature of industrial-technological civilization, regardless of our ability to produce artificial consciousness.

Once these demanding engineering problems are resolved, industrial-technological civilization will need to look further afield in its maturity for multi-generational projects that can continue to stimulate the STEM cycle and thus maintain that civilization in a vital, vigorous, and robust form. A starship would be the ultimate scientific instrument produced by technological civilization, constituting both a demanding engineering challenge to build and offering the possibility of greatly expanding the scope of scientific knowledge by studying up close the stars and worlds of our universe, as well as any life and civilization these worlds may comprise. This next great challenge of our civilization, being a challenge so demanding and ambitious that it could come to be the central motif of industrial-technological civilization in its maturity, could be called the interstellar imperative, and we ourselves may be the Axial Age of industrial-technological civilization that first brings this vision into focus.

Even if the closest stars prove to be within human reach in the foreseeable future, the universe is very large, and there will be always further goals for our ambition, as we seek to explore the Milky Way, to reach other galaxies, and to explore our own Laniakea supercluster. This would constitute a civilizational imperative that could not be soon exhausted, and the civilization that sets itself this imperative as its central organizing principle would not lack for inspiration. It is the task of Project Astrolabe at Icarus Interstellar to study just these large-scale concerns of civilization, and we invite interested researchers to join us in this undertaking.

Image: Frau im Mond, Fritz Lang, 1929.

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Jacob Shively, Heath Rezabek, and Michel Lamontagne read an earlier version of this essay and their comments helped me to improve it.

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Notes

[1] I have specified intelligence emergent from a brain that supervenes upon a limbic system because in this context I am concerned with peer intelligence. This is not to deny that other forms of intelligence and consciousness are possible; not only are they possible, they are almost certainly exemplified by other species with whom we share our planet, but whatever intelligence or consciousness they possess is recognizable as such to us only with difficulty. Our immediate rapport with other mammals is sign of our shared brain architecture.

[2] No. 205 in the Brunschvicg ed., and Pascal again: “I see those frightful spaces of the universe which surround me, and I find myself tied to one corner of this vast expanse, without knowing why I am put in this place rather than in another, nor why the short time which is given me to live is assigned to me at this point rather than at another of the whole eternity which was before me or which shall come after me. I see nothing but infinites on all sides, which surround me as an atom and as a shadow which endures only for an instant and returns no more.” (No. 194)

[3] Or our extraterrestrialization might have happened much earlier in human civilization, as Carl Sagan imagined in his Cosmos: “What if the scientific tradition of the ancient Ionian Greeks had survived and flourished? …what if that light that dawned in the eastern Mediterranean 2,500 years ago had not flickered out? … What if science and the experimental method and the dignity of crafts and mechanical arts had been vigorously pursued 2,000 years before the Industrial Revolution? If the Ionian spirit had won, I think we—a different ‘we,’ of course—might by now be venturing to the stars. Our first survey ships to Alpha Centauri and Barnard’s Star, Sirius and Tau Ceti would have returned long ago. Great fleets of interstellar transports would be under construction in Earth orbit—unmanned survey ships, liners for immigrants, immense trading ships to plow the seas of space.” (Cosmos, Chapter VIII, “Travels in Space and Time”)

[4] While there are few examples of truly difficult engineering problems as we understand them today (i.e., in scientific terms) prior to the advent of industrial-technological civilization, because, prior to this, technical problems were only rarely studied with a pragmatic eye to their engineering solution, agrarian-ecclesiastical civilization had its multi-generational intellectual challenges parallel to the multi-generational scientific challenges of industrial-technological civilization — these are all the familiar problems of theological minutiae, such as the nature of grace, the proper way to salvation, and subtle distinctions within eschatology. And all of these problems are essentially insoluble for different reasons than a particularly difficult scientific problem may appear intractable. Scientific problems, unlike the intractable theological conflicts intrinsic to agrarian-ecclesiastical civilization, can be resolved by empirical research. This is one qualitative difference between these two forms of civilization. Moreover, it is usually the case that the resolution of a difficult scientific problem opens up new horizons of research and sets new (soluble) problems before us. The point here is that the monumental architecture of agrarian-ecclesiastical civilization that remains as its legacy (like the Duomo of Florence, used as an illustration here) was essentially epiphenomenal to the central project of that civilization.

[5] An entertaining account of the building of the dome of the Florence Duomo is to be found in the book The Feud That Sparked the Renaissance: How Brunelleschi and Ghiberti Changed the Art World by Paul Robert Walker.

[6] On the agrarian-ecclesiastical imperative: It is at least possible that the order and stability cultivated by agrarian-ecclesiastical civilization was a necessary condition for the gradual accumulation of knowledge and technology that would ultimately tip the balance of civilization in a new direction.

[7] While the use of the phrase “STEM cycle” is my own coinage (you can follow the links I have provided to read my expositions of it), the idea of our civilization involving an escalating feedback loop is sufficiently familiar to be the source of divergent opinion. For a very different point of view, Nassim Nicholas Taleb argues strongly (though, I would say, misguidedly) against the STEM cycle in his Antifragile: Things That Gain from Disorder (cf. especially Chap. 13, “Lecturing Birds on How to Fly,” in the section, “THE SOVIET-HARVARD DEPARTMENT OF ORNITHOLOGY”); needless to say, he does not use the phrase “STEM cycle.”

[8] This list of challenging technologies should not be taken to be exhaustive. I might also have cited high temperature superconductors, low energy nuclear reactions, regenerative medicine, quantum computing, or any number of other difficult technologies. Moreover, many of these technologies are mutually implicated. The development of high temperature superconductors would transform every aspect of the STEM cycle, as producing strong magnetic fields would become much less expensive and therefore much more widely available. Inexpensive superconducting electromagnets would immediately affect all technologies employing magnetic fields, so that particle accelerators and magnetic confinement fusion would directly benefit, among many other enterprises.