Conjure an image in your mind: a pencil resting on a small table, perhaps next to a notebook. In what position did you imagine the pencil? Lying on its side, right? Why not upright, with either the eraser or the graphite tip touching the table and the rest pointing into the air?
In terms of strict physical forces, it’s possible to position a pencil this way. We never see it happen because even the tiniest vibration, from the rumble of someone tapping the table to a slight shift in air currents, will knock it over.
The upright pencil is in what’s called unstable equilibrium, a state of being that can exist if unperturbed, but that will change rapidly if given the tiniest shock from the physical world. By contrast, a pencil lying on its side is in stable equilibrium. Blow on it, even slam your ﬁst on the table, and the pencil will stay in that position or bounce around momentarily and then go back to it.
Stable equilibria are generally more important than unstable, because things in such states stay there. Whether we’re thinking of forces affecting a pencil or the Dow Jones Industrial Average, we can expect something to remain near a stable equilibrium but to wander away from an unstable one. So whenever we consider a state of equilibrium, we’ve got to ask whether it’s stable.
For several decades, academics have assumed that the economy is in a stable equilibrium. Distilled into a few elegant lines of mathematics by the economists Kenneth Arrow and Gerard Debreu back in the 1950s, the assumption has driven most thinking about business cycles and financial markets ever since. It informs the idea, still prevalent on Wall Street, that markets are efficient -- that the greedy efforts of millions of individuals will inevitably push prices toward some true fundamental value.
Problem is, all efforts to show that a realistic economy might actually reach something like the Arrow-Debreu equilibrium have met with failure. Theorists haven’t been able to prove that even trivial, childlike models of economies with only a few commodities have stable equilibria. There is no reason to think that the equilibrium so prized by economists is anything more than a curiosity.
It’s as if mathematical meteorologists found beautiful equations for a glorious atmospheric state with no clouds or winds, no annoying rain or fog, just peaceful sunshine everywhere. In principle, such an atmospheric state might exist, but it tells us nothing about the reality we care about: our own weather.
Outside economics, in areas such as meteorology, the biggest shift in scientific thinking of the last 50 years has been the movement to understand “out of equilibrium” systems. Consider tornadoes. The state of Kansas alone sees hundreds of them every year, and they come about through perfectly ordinary atmospheric processes. Warm, moist air sweeps in from the Gulf of Mexico, cold air descends from the Rockies, surface winds blow. All these events build on one another, and soon an ordinary gray sky becomes a violent, memorable twister.
More technically, we could say that the atmosphere is prone to positive feedbacks, which prevent it from settling into a nice equilibrium. As humans, we’re terrible at imagining how such processes work. Take a piece of paper and fold it, and then take that doubled paper and fold it again, and then again, 30 times in all. Actually, don’t waste your time. You’ll find you can’t do it because the result, if you did, would be about 70 miles thick. This is the power of positive feedback: Each step not only makes things bigger, but also makes them bigger more quickly. This leads to consequences far beyond our expectations.
In one form or another, positive feedback lies behind almost everything that makes our world rich and surprising, changeable and dynamic, lively and unpredictable. It makes seeds sprout and grow into trees, matches burst into flame, and single cells divide and proliferate into living, thinking human beings. It drives political revolutions and new religions. Yet outside of these areas, an intellectual blind spot to the power of positive feedbacks still holds us back. Nowhere is this truer than in the science of human systems, in social science, and especially in economics and finance.
We’ll never understand economies and markets until we get over the nutty idea that they alone -- unlike almost every other complex system in the world -- are inherently stable and have no internal weather. It’s time we began learning about the socioeconomic weather, categorizing its storms, and learning either how to prevent them or how to see them coming and protect ourselves against them.
(Mark Buchanan, a theoretical physicist, is the author of “The Social Atom: Why the Rich Get Richer, Cheaters Get Caught and Your Neighbor Usually Looks Like You.” This is the first in a series of three excerpts from his new book, “Forecast: What Physics, Meteorology and the Natural Sciences Can Teach Us About Economics,” to be published March 26 by Bloomsbury. The opinions expressed are his own.)
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