OneThing30: learn to love the feedback loop

When it comes to systems, shift happens

Michigan's Big House - a place with an actual carrying capacity

Jay Wright Forrester

Cornhusker Jay Forrester

Jay Forrester famously and emphatically stated once to a room of virgin system modelers that all flows are controlled by stocks. Period.  There is no such thing as a flow controlling a flow.  Really? I get it, and he is certainly many dozens of IQ point smarter than I . . . but come on . . . there’s probably somewhere in this universe where a flow controls a flow, right?

“It is the nature of systems that a flow is controlled by a stock.”

With football games starting up around the country . . . and my own beloved, though probably venal Oregon Ducks starting today against LSU . . . I thought about the carrying capacity of various stadiums around the US.  Yeah . . . we can show loop dominance and shifting loop dominance and a stock controlling a flow this.  Totally.

Reaching Carrying Capacity at your local, crazed college football stadium

In this quick-n-dirty model depicting the stock of fans at the Big House, I took some care to highlight the feedback loop:  as the crowd closes the gap between actual and capacity the pace of entering slows down and, of course, will stop.  (Of course, someone might pay off an usher or two, break fire marshal laws so more coeds could jam the aisles and stands. Different story.)

Just another Saturday in Ann Arbor

The size of the stock dictates the size of the flow.  Period.

This same model applies to the cars in the parking lot, the space available at the tailgating venues, the line into restrooms at halftime, the flow of students into classes on Monday mornings, and on the list goes.

In schools across the country, families will fill cars, students will climb onto buses as they return to classrooms, gymnasiums, cafeterias, hallways, lockerrooms, and auditoriums.  And it will operate in the same way – the size of a stock will control the size of the flow.


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