There is a sub-branch of the study of dynamic systems called Catastrophy Theory. Despite the name, it doesn’t deal with earthquakes and tsunamis. Instead, it deals with situations in which perturbed dynamic systems don’t revert when the perturbation is reversed (OK, yes, earthquakes and tsunamis can do that). Raising the price of public transport might well trigger a drop in ridership. Returning the price to the original value might not cause ridership to return to its previous high.
Similarly, Chaos Theory talks about basins of attraction. A chaotic system will tend to move unpredictably within one region, or basin, but if it stumbles upon the right path it might well flip over into a different basin, whereupon it will start moving unpredictably within that one. Attempting to retrace the steps most likely won’t return you to the previous basin because of, you know, chaos. One of the concerns about climate change is that we might drive the Earth’s climate into a new basin of attraction, one that is stable, but inimical to human civilization.
Both of these have some of the attributes of a one-way function. Chaos Theory because finding your way back is so hard, Catastrophe Theory because retracing your steps brings you somewhere else. Think of being on the edge of an overhanging cliff. If you walk towards the cliff long enough, you fall over the edge. If you turn around, once you hit bottom, and walk back the way you came, you don’t end up on top of the cliff, you end up underneath the overhang. Returning to the top requires that you walk the long way around.
Getting hit by a modest sized asteroid is like that. Or a comet.
Over on Next Big Future is a chart showing the threat posed by various sizes of asteroids, should they hit the Earth. Imperial College, London, has a handy calculator, plus a 2.5MB pdf document, providing a little more detail. The ICL simulator is quite a bit more sanguine than is NBF. Their description of a 500m diameter asteroid impact reads like a largish nuclear warhead strike, while NBF considers it a civilization-ending event. Let’s agree that nobody is sure how big of an asteroid strike is needed to cause civilization to collapse, and that we can only guess at the likelihood of that happening within the lifetime of our current civilization. That’s not the problem.
The problem is this. Modern civilization is a one-time event. If it goes away, it isn’t coming back.
Think of what a civilization-ending impact might be like. If a sufficiently large asteroid (or comet) hits in the Pacific Ocean — the most likely event — everything on the Pacific Rim disappears in the super-tsunami. Or maybe it lands in Siberia (the last two did), so we get world-wide firestorms. Wheatever happens, the materials thrown into the atmosphere will likely give us two or five or ten years of nuclear winter. Everybody starves. Well, everybody in First World Europe and Asia and North America. Equatorial peoples are the most likely to survive. Even if there are enclaves in the First World, they’re not likely to include a particularly wide range of technology skills — they’ll be tinkerers, not engineers. I’m not going to go into detail because that’s not what I want to discuss. I’m assuming an impact big enough to destroy all but a fraction of modern civilization while allowing a biggish chunk of humanity to survive. How big of a rock is that? You decide. You want more detail? Read Niven and Pournelle‘s 1977 book Lucifer’s Hammer, then turn it up to eleven.
The question is, what happens when the majority of the survivors of a global catastrophe get knocked back to at best an early 18th Century mode of existence (and at worst an early 8th Century mode), mitigated by a dwindling cache of manufactured goods and a vague memory of what is possible? It took us 250 years to go from the technology of colonial America to our current 21st Century position. Can we do it again? In 250 years? Not likely.
You see, modern civilization is energy intensive. Cheap energy intensive. Which means petrochemicals. The reason it’s so hard for us to give up our oil dependency is that oil is the only resource that checks all the boxes for energy density, transportability, and so forth — here’s a pair of comparison tables from Do The Math.
More to the point, the movement from a society dependent on 18th Century technology to one that wears 21st Century technology on its wrist requires an enormous amount of energy. So, solar panels can provide energy, but where do we get the energy to go from steam engines to a wafer fab for solar cells? Access to today’s coal resources requires the ability to dig tunnels a thousand feet beneath the ground, or to remove the top thousand feet off a mountain. Most of today’s sources of oil now require high-tech methods to access and process them. Can you spell deep ocean drilling? Hydraulic fracturing? Cyclic steam stimulation? Combustion overhead gravity drainage? The few remaining sources of post-impact easy oil are likely to be used up heating the homes and powering the cars of third-world locals, until those resources are also gone. I’d be off on a rant about the last peasants using the last of the oil, if I weren’t pretty sure that at the same time the last Americans and last Europeans weren’t burning the last books, to keep from freezing.
This is not even a rant about our using all the pre-impact oil. That’s a sunk cost. We thought we had good reasons for doing what we did, at the time we did it, and now we are where we are. This is a warning that we only get one shot at creating a viable space-based civilization, one that’s independent of planetary resources, and dispersed enough to keep us safe from the real dinosaur-killer rocks that are out there. I’m not the first to raise this issue. I think that Niven and Pournelle actually did that, thirty or forty years ago. I’m just taking advantage of recent events to casually drop the idea into our Thanksgiving dinner conversations.