Pippard’s Ladder
Climate change, technology innovation, and the seductive lure of seemingly-predictable behavior
Based on a draft chapter section that didn’t make the final cut for the book Films from the Future: The Technology and Morality of Sci-Fi Movies.
In 1980, the Cambridge physicist Brian Pippard published a somewhat obscure paper with the title “Demonstration experiments in critical behavior and broken symmetry”. Pippard was an accomplished experimentalist and educator, and keenly aware of the near-impossibility of deducing some aspects of the physical world without hands-on experimentation.
In this particular paper, he was interested in discontinuities and critical transitions — what some people might call tipping points today. In his words, to physics students of the time:
“the idea of continuity is almost a religious principle. Yet discontinuities of one sort or another pervade our everyday lives — a dripping tap, a snapping branch, a breaking wave — and in the professional life of a physicist provide some of the most interesting and recalcitrant problems.”
Pippard was acutely aware that, in the real world, things aren’t always as predictable and well behaved as we’d like them to be, and he set about designing a series of class experiments to demonstrate this.
I probably wouldn’t be aware of Brian Pippard’s work if I hadn’t been a PhD student in the Cavendish Laboratory at Cambridge when he was Professor Emeritus there. Even then, I wasn’t particularly familiar with his work, apart from one notable public lecture that he gave in the early 1980's.
In the lecture, Pippard used one of the examples from his 1980 paper to illustrate a deceptively simple critical transition. In the demonstration, Pippard vertically held a miniature rope ladder with four evenly spaced rungs between his hands, and asked the audience what they would expect to happen as he slowly rotated the bottom rung through a complete horizontal revolution.
Based on predictions from the initial rotation of the rung, the ladder would be expected to smoothly transform into something that looks like a strand of DNA — a neat double helix, made up of the two rope supports and the four rungs.
Of course — and this is an experiment anyone can try by reconstructing the ladder in Pippard’s paper — things didn’t go smoothly. At some point, although it was fiendishly hard to predict exactly when it would occur, the rope between two of the struts suddenly twisted and tangled, releasing the built-up tension and destroying any semblance the ladder had to a strand of DNA.
I must confess I remember nothing else from the lecture. But this image has stuck with me. This was due in part, I suspect, to my then-advisor muttering something about “Pippard and his bloody ladder” under his breath. But mainly it was because it was such an elegant demonstration of how seemingly stable systems can undergo rapid, transformative, and hard to reverse change in the blink of an eye — and often in defiance of how we expect them to behave!
Tipping points
Since Pippard’s 1980 paper, it’s become increasingly trendy to talk about tipping points — hard-to-predict points of instability in seemingly stable systems. This is especially the case in the context of climate change, but tipping points (or nonlinear instabilities if you want to get technical) are also relevant to the potential impacts of advanced technology innovation.
Like Pippard’s ladder, the concern around human action-driven climate change is that, we’ll hit points of instability that lead to rapid and hard-to-predict change which are challenging or impossible to reverse. And also like the rope ladder analogy, there’s a growing fear in some quarters that assumptions over how the environment should behave may prove to be spectacularly incorrect.
It’s fears like these that lie at the heart of the changes seen in the movie The Day After Tomorrow (which for all its silliness and implausibility, grapples with this idea of climactic tipping points).
In the movie, the disintegrating Antarctic ice shelf is the tipping point that initiates a sudden change in ocean currents, pushing the world into a new and radically different climate regime — and one that has deep social and economic consequences. The catastrophic changes that play out are of course hopelessly unrealistic. Yet the underlying idea that we could inadvertently push the world into a new set of climactic conditions and dynamics is not so far-fetched. And while a simple rope ladder may seem like a ridiculously simplistic demonstration of the power of critical tipping points, it’s deeply revealing of the increasingly fine line we’re treading as we continue to push the world’s climate to the limit.
What is particularly startling here is that, even with something as simple as a four-rung rope ladder, it’s extremely hard to predict where and when a tipping point in behavior will occur. Imagine then how hard then it is to predict how seemingly small events — slightly more carbon dioxide being emitted into the atmosphere; a shift in methane releases from warming permafrost; increasingly unstable ice sheets — might lead to rapid and irreversible climate change. The same goes for the predictability of environmental, social, or even political, impacts of technologies like gene editing, artificial intelligence, and a whole host of others.
When it comes to climate change, the good news is that the indications from current models suggest our climate is less likely to suddenly tip over into a radically different state than it might sometimes seem. Precisely because the planet is more complex than a four-rung ladder, it has more ways of absorbing and adapting to changes than Pippard’s demonstration. And while there are indications that local tipping points may be reached, there’s less concern amongst climate scientists that we’ll see sudden and irreversible global catastrophic changes.
Yet just because our models — which for all their sophistication are pretty crude predictors of how severe the impacts of climate change will be — suggest catastrophic climate tipping points are unlikely, it doesn’t mean we should be complacent. Fortunately, even though scientists cannot predict precisely where and when climate tipping points may occur, they can say with some certainty what is likely to increase their likelihood, and what we can do to stave them off as long as possible. And just as the best way to avoid the transition change with Pippard’s rope ladder is to stop turning the bottom rung, the best way to avoid climate tipping points is to stop over-stressing the climate.
This is of course easier to say than to do. Yet the harsh reality is that there are likely to be some environmental tipping points in our collective future, and the two choices we face are what we’re going to do to keep them in the future, or how we’re going to prepare for when they occur.
How we respond to this challenge depends in part on how we think about the world we live in and the future we’re building; and how we bring together science, technology, and what’s important to us, to chart our way forward. Yet this is something that goes far beyond climate change, and gets to the very heart of how we innovate responsibly.
Pippard’s Ladder and Emerging Technologies
There’s always been a complex connection between the technologies we develop and use, and the world we live in. Agricultural practices, urbanization, use of fossil fuels, electricity, genetic engineering, information and computing technology, and many others; all have moulded our world in ways which have, in turn moulded, the ways we live our lives. Yet as the coupling between what we do and how it affects us and the planet we live on has tightened, the consequences of this coupling have become increasingly hard to predict.
In effect, we live in a technological age that is pushing us closer and closer to the metaphorical tipping point in Pippard’s Ladder, but we still lack the ability to predict precisely when we’ll hit the point of no return, or what the world will look like after.
Of course, it’s tempting to look back in history and claim that many technological advances so far have led to positive outcomes, or at least have not led to the catastrophic predictions that some have predicted. And this is has a ring of truth about it , at least for some technologies, if not all.
And yet, this is precisely the point of Pippard’s demonstration: In a complex system, what has occurred in the past does not adequately predict what will happen in the future.Are we reaching such a point with the technologies we’re now developing? It’s hard to tell. But without a doubt there is a growing tension between what we can achieve with powerful technologies, the growing demands of a global population, and the constraints imposed by living within planetary boundaries, that is indicative of a highly complex and increasingly unstable system.
And just like with climate change, we have a choice: Do we continue to charge full-steam ahead with technologies like AI, gene editing and others until something gives (and we cross our fingers and hope it’s not a Pippard’s Ladder-like transition)? Or do we get serious about how to innovate responsibly, so we don’t jeopardize the future simply because we were naive enough to assume it would be just like the past?
This, to me, is the lasting lesson of that 1980’s lecture, and a ladder that didn’t behave as we though it should.
Adapted from an early draft of Films from the Future: The Technology and Morality of Sci-Fi Movies (this didn’t make it’s way to the final published version!)
