The Sandpile Paradigm

A (W.T2.F.) Sunday Series

Short Story Time

Andy’s out in Santa Monica surfing and catches a wave to shore for a break. He sits on the beach, running small grains of sand through his hand.

As he watches the movement of sand, he begins to think of the sandpile paradigm that explains the concept of self-organized criticality. It’s one of the many concepts that contribute to the chaos theory and is a way to make sense of catastrophism that arises from complexity in nature.

The sandpile paradigm was a fantastic comparison, and now that Andy has his very own live demo, he moves to his belly for a first hand account of the movements of the sandpile.

Letting the grains through his hand very slowly, he watches as they cascade down the side of the growing sandpile. After a few seconds, he observes a miniature avalanche where a large section of the pile tumbles down in a wave of sand. This pattern continues to repeat in relatively steady increments as he continues to add sand to the pile.

As he recalls, these avalanches are called an emergent phenomena. It’s the case where the large avalanches (not the gradual change of individual grain movements) form the basis for the emergent phenomena, or the event of ‘catastrophic change.’

So even though there are many smaller events (the slow cascade of sand grains down the side of the pile) it’s the larger, catastrophic events that are responsible for most of the changes in the sandpile, or system.

Another way to describe each avalanche is as the self-organized critical state. Andy notes that this is when the sandpile can no longer organize the additional sand in the current system (when the slope reaches a certain value and can no longer increase) so other grains of sand are forced to leave the system. These occasional avalanches span the entire pile as an example of the self-organized critical (SOC) state.

Now, Andy stops the flow of sand to make sense of his observations and grins as this reminds him of yet another part of the paradigm. Without the input of sand, the pile is in the stationary SOC state. The avalanches, or the critical state, can only be maintained when there is an inflow of new sand, or energy, into the system.

So, in a nutshell, he now understands how SOC is nature’s way of going through massive transformations over short time scales. From the slow movement of the Earth’s crust that result in catastrophic quakes, to mass extinctions in a short period of time, Andy has learned a bit more about How Nature Works.

A (W.T2.F.) Series

By @scifiannemarie

Note: The sandpile paradigm is an example of SOC from the book How Nature Works by Per Bak 🙂

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