The big question for this segment is, how and why do complex systems break down? [MUSIC] Shelley's famous poem, Ozymandias, is about a great emperor whose statue was found in the desert. Shelley was probably thinking of a statue of Pharaoh Ramesses II, who lived more than 3,000 years ago. In Shelley's poem, the writing on an ancient pedestal boasts, My name is Ozymandias, king of kings, look on my works, ye mighty, and despair. The poem ends, Nothing beside remains, round the decay of that colossal wreck, boundless and bare, the lone and level sands stretch far away. Ozymandias got on the wrong side of the second law of thermodynamics, and so will all complex systems, including you and me. But why do they break down? And can we learn ways of stabilizing them for a bit longer? Let's go back to a graph we've already used earlier in this course, Eric Chaisson's graph showing the density of flows of free energy through different complex things. Chaisson's idea, you'll remember, is that, roughly speaking, very roughly, more complex things depend on denser flows of free energy than simpler things. If his calculations are right, and they are neither easy to do nor uncontroversial, they suggest that the world of the Anthropocene represents a sort of pinnacle of complexity. But there's something else in the graph. The horizontal axis shows how long different complex systems survive. It's a rough measure of stability. By Chaisson's measures, our sun may be simpler than modern human society, but, as the graph shows, it will survive for about 9 billion years before starting to break down. Living organisms may be much more complex, but their lifespans are hundreds of millions of times shorter than the sun's. Species, as opposed to individuals, can survive often for a few million years. But our own species has existed for less than 200,000 years so far. And modern industrial societies have existed for about 200 years, or one-thousandth of the lifespan of our species. There is a hint here of another powerful rule, which is that more complex things may be more fragile than simpler things. Because they depend on much denser flows of energy, and maintaining those flows at precisely the right level, not too small, but not so large as to be destructive, is a very delicate business. Particularly as all their component parts tend to pull in slightly different directions. This module is about how complex systems break down. Even complex physical systems, such as the sun, will break down. Like all stars, the sun's break down will be messy and violent. But, by solar standards, it'll be quite tame. When the very largest stars break down, they die in supernova explosions so large that for a few days or weeks, they may outshine an entire galaxy. Complex adaptive systems seem to break down more easily than complex physical systems. We can think of the entire biosphere as a complex system. And it, too, has evolved, as the movements of tectonic plates and changes in living organisms have generated powerful, and sometimes dangerous, feedback systems. For example, quite early in the history of planet Earth, some organisms learn to feed off highly energetic photons from the sun. We call this photosynthesis. But a side effect of photosynthesis was the production of lots of oxygen, a gas that was poisonous to most early organisms. So how close did life as a whole come to collapse? We don't know, but we do know that the biosphere went through a torrid time. And this was one of many mass extinctions in which large numbers of species vanished as a result of changes that upset delicate balances within the biosphere. Today, we're living through one more of these events. But this time, the cause is not evolutionary events, or continent-wide volcanic eruptions, but human activity. We humans are now using the energy and resources of the biosphere on such a huge scale that other species are suffering. Many are now in danger of extinction. Human societies, too, can collapse, like Ozymandias' empire, and they’ve done so many times. Why? We can point to many particular reasons, but have no general explanation. Often, it was because they overexploited the resources on which they depended. And suddenly found they were running short of the energy they needed to sustain themselves. In today's world, though, our technologies are so powerful that we may face the opposite problem. We have too much energy, so much that our weaponry could destroy much of the biosphere in just a few hours. And our industries could destabilize the Earth's climate systems. The world wars of the 20th century offered just a glimpse of these dangers. Modern economies are also extremely complex. And, like all complex systems, they can flip unexpectedly, as they did during the global financial crisis of 2008. Modern economic theory assumes stability, or equilibrium, as a sort of norm. But seen in a larger context, it is change and transformation that are the norm. Are our economic models so out of date that they hide important sources of instability in the global economy? Or is it possible that it's new technology, such as flash trading, that are destabilizing the economy? Either way, we need to be aware of the fragility of a system as complex as the modern global economy. So this module points to one further aspect of complexity. When complex systems break down, their fragments often provide the pieces from which new complex systems will be assembled. The extinction of the dinosaurs allowed mammals to flourish. The economic boom of capitalist societies in the second half of the 20th century was a sort of rebound from the destruction of the first half of the century. Do we have enough understanding of the colossal complexity of modern society to ensure that we can take advantage even of the crises it will surely endure in the next century? [MUSIC]
