Late Summer Sandpile

Ubiquity, Complexity Theory, and Sandpiles
Fingers of Instability
A Stable Disequilibrium
No More Business Cycles
Birthdays and Books

Last week, I said I would continue writing about Michael Gurri’s important book, The Revolt of the Public. It turns out giving a proper review of not just the book but all of the comments about the book will require more than a few days’ writing. I am going through almost 100 pages of new comments and quotes from the book and other essayists.

That being the case, I’m moving up a letter I was planning to share with you on my birthday weekend in two weeks. The story about sandpiles and the financial system may be the most popular letter I’ve written in the last 25 years. It is one we should all re-read every few years to remind us how change happens slowly, then suddenly. It is actually a good time given that I am talking about an upcoming crisis and some significant changes ahead. The Gurri book explains some of the reasons.

So, without further comment, let’s think about that single grain of sand that collapsed the sandpile.

Ubiquity, Complexity Theory, and Sandpiles

I’ll be quoting from a very important book by Mark Buchanan called Ubiquity, Why Catastrophes Happen. I HIGHLY recommend it if you, like me, are trying to understand the complexity of the markets. The book isn’t directly about investing—although he touches on it—it’s about chaos theory, complexity theory, and critical states. It’s written so anyone can understand—no equations, just easy-to-grasp, well-written stories and analogies.

As kids, we all had the fun of going to the beach and playing in the sand. Remember taking your plastic bucket and making sandpiles? Slowly pouring the sand into ever bigger piles until one side of the pile starts to collapse?

Imagine, Buchanan says, dropping one grain of sand after another onto a table. A pile soon develops. Eventually, just one grain starts an avalanche. Most of the time, it’s a small one. But sometimes, it builds up, and it seems like one whole side of the pile slides down to the bottom.

Well, in 1987, three physicists named Per Bak, Chao Tang, and Kurt Wiesenfeld began to play the sandpile game in their lab at Brookhaven National Laboratory in New York. Actually piling up one grain of sand at a time is a slow process, so they wrote a computer program to do it. Not as much fun, but a whole lot faster. Not that they really cared about sandpiles; they were more interested in what are called “nonequilibrium systems.”

They learned some interesting things. What is the typical size of an avalanche? After a huge number of tests with millions of grains of sand, they found out there is no typical number. Quoting Buchanan:

“Some involved a single grain; others, ten, a hundred, or a thousand. Still others were pile-wide cataclysms involving millions that brought nearly the whole mountain down. At any time, literally anything, it seemed, might be just about to occur.”

The pile was indeed completely chaotic in its unpredictability. Now, let’s read this next paragraph slowly. It is important as it creates a mental image that helps clarify the organization of the financial markets and the world economy.

“To find out why [such unpredictability] should show up in their sandpile game, Bak and colleagues next played a trick with their computer. Imagine peering down on the pile from above and coloring it in according to its steepness. Where it is relatively flat and stable, color it green; where steep and, in avalanche terms, “ready to go,” color it red. What do you see? They found that at the outset, the pile looked mostly green, but that, as the pile grew, the green became infiltrated with ever more red. With more grains, the scattering of red danger spots grew until a dense skeleton of instability ran through the pile. Here then was a clue to its peculiar behavior: a grain falling on a red spot can, by domino-like action, cause sliding at other nearby red spots.

“If the red network was sparse, and all trouble spots were well isolated one from the other, then a single grain could have only limited repercussions. But when the red spots come to riddle the pile, the consequences of the next grain become fiendishly unpredictable. It might trigger only a few tumblings, or it might instead set off a cataclysmic chain reaction involving millions. The sandpile seemed to have configured itself into a hypersensitive and peculiarly unstable condition in which the next falling grain could trigger a response of any size whatsoever.” (Emphasis mine. —JM)