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positive feedback
the norbert wiener story
by dirk cotton

I didn’t sleep well last night and that got me to thinking about positive feedback loops. (Don’t you hate it when that happens?) I learned about them in a college class decades ago. I believe it was a psychology class, of all places.

Since you may have been spared that particular lecture, let me give you a little background. And, I will apologize in advance for this story taking “the long way around the barn”, as we used to say when I was growing up, but please bear with me.

The concept of feedback loops was introduced by Norbert Wiener in his 1948 work on cybernetics. That isn’t really important to my story, but I’d hate to miss an opportunity to say “Norbert Wiener”. Doesn’t seem to add much to my credibility, I’ll admit, to say my thoughts are based on the works of a man named Norbert Wiener, but there you have it.

In a nutshell, negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes to the system are lessened.

The thermostat in your home creates a negative feedback loop. Your furnace heats the house until at some point the thermostat figures it’s warm enough and shuts off the furnace. The house then gradually gets colder, so at some point the thermostat turns the furnace back on. Negative feedback loops can work pretty well.

In contrast, positive feedback occurs when the output of a system acts to increase changes to the input of the system, with the result that the changes are amplified.

If you’ve ever heard microphone feedback, you’ve experienced a positive feedback loop. Sounds go into a microphone held too close to the speaker. The amplifier increases the volume and that louder volume goes back into the microphone, which gets amplified again, over and over.

About one second into this positive feedback loop, the voice spoken into the microphone is re-amplified several times, resulting in a head-splitting scream from the speakers (except when Jimi Hendrix did it intentionally with his guitar, in which case it ended up sounding remarkably cool).

Given enough energy, a positive feedback system will ultimately destroy itself. Imagine that your thermostat actually turned the heat up instead of down when the house got warmer. With a powerful enough furnace, the house would eventually burn down.

Now, those few persistent readers who have hung with me this long are no doubt wondering what any of this has to do with my inability to sleep last night and the answer is “an electric blanket”.

My wife and I changed the bed sheets yesterday and inadvertently reversed the individual controls on our dual electric blanket. She likes to sleep warmly and I prefer to be a little cool.

After we went to bed, I noticed that my side was unusually warm, not realizing that was because I was sleeping under her side of the blanket. (I don’t do my best thinking when I’m half asleep.) I clicked the heat down a couple of notches on the control next to my side of the bed.

Unfortunately, the wire from that remote control next to me ran around the foot of the bed and connected to my wife’s side of the blanket.

She had already noticed the bed was cooler than usual, again not knowing that she was sleeping under my side of the electric blanket, so she cranked up the heat on the control next to her (my control, normally), making my side of the bed even hotter, but having no effect whatsoever on her side.

I was too sleepy to notice that setting my remote control a little cooler had actually resulted in my side of the bed becoming warmer, so I cranked the control next to me down yet another notch, making her even colder, and the positive feedback loop was in full operation. This process evolved over several hours and by the time I had turned my electric blanket remote control all the way down to OFF, I was sweltering. Meanwhile, my wife had cranked the control on her side of the bed to 10 by that time and she was shivering.

By about 4:00 a.m., my wife had taken matters into her own hands and pulled all of the cover, including both halves of our electric blanket, onto her side of the bed, leaving her feeling toasty and leaving me just a tad cooler than I had really wanted to be.

The next morning I was about to shower when I heard my son and his wife come in downstairs. As they exchanged Christmas greetings with my wife, I heard my son mention that he wanted to take a shower. I ran to my shower, because my son is the only person I know who takes longer showers than me and I wanted to finish before he used all the hot water.

I ran the water for a minute or so until it was nice and hot and jumped in. A few minutes later, the water turned cold and I realized than my son must have started the shower upstairs.

I had to open the hot water faucet further to return the heat to my shower and that worked for about a minute. When the water turned cool again, I was pretty sure that my son and I were dueling for hot water and that’s when I realized that the remote controls on the electric blanket must’ve gotten reversed.

Eventually, we reached some sort of "Nash" equilibrium point where both of us were standing in tepid streams of water and nothing either of us did could improve our situation. I got frustrated with the entire sleeping/bathing positive feedback loop malarkey and shut off my shower abruptly.

“Dammit!” I slammed the faucet in with my palm and the water shut off. I heard a scream and several cuss words coming from upstairs and realized that my son now had plenty of hot water. (Guess I hadn’t thought that one through all the way.)

Anyway, that’s how my sleepless night reminded me of a college lecture on a subject in which the seminal work was done by one Norbert Wiener, whose name I love to say. Fortunately, neither the electric blanket nor the hot water system had enough power to actually destroy itself.

Sometimes, an out-of-control positive feedback system only has enough energy to make you cuss.

I suppose I should pass that finding along to Norbert Wiener.

Heh heh. I said it again.


Dirk Cotton is a retired executive of a Fortune 500 Internet company who loves to spend time with his family, fly fish, shoot sporting clays, attend college baseball games, sail, follow the Wildcats, and write. Everything else he does is just for fun. A computer programmer-cum-marketing executive-cum-financial planner who now wants to be a writer, he apparently can't decide what he wants to be when he grows up. He and his family moved to The Southern Part of Heaven in 2005 and couldn't be happier with that decision.

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