What We Can’t Foresee

by Patrick Appel

Dan Gardner and Philip Tetlock encourage humility in prediction making:

Natural science has discovered in the past half-century that the dream of ever-growing predictive mastery of a deterministic universe may well be just that, a dream. There increasingly appear to be fundamental limits to what we can ever hope to predict. Take the earthquake in Japan. Once upon a time, scientists were confident that as their understanding of geology advanced, so would their ability to predict such disasters. No longer. As with so many natural phenomena, earthquakes are the product of what scientists call “complex systems,” or systems which are more than the sum of their parts.

Complex systems are often stable not because there is nothing going on within them but because they contain many dynamic forces pushing against each other in just the right combination to keep everything in place. The stability produced by these interlocking forces can often withstand shocks but even a tiny change in some internal conditional at just the right spot and just the right moment can throw off the internal forces just enough to destabilize the system—and the ground beneath our feet that has been so stable for so long suddenly buckles and heaves in the violent spasm we call an earthquake. Barring new insights that shatter existing paradigms, it will forever be impossible to make time-and-place predictions in such complex systems. The best we can hope to do is get a sense of the probabilities involved. And even that is a tall order.