Image courtesy of Pixabay

Image courtesy of Pixabay

By XiaoZhi Lim
Quanta

Mustafa Khammash’s small Lego robot is engaged in a one-way staring contest with a book held 30 centimeters in front of it. Khammash slides the book forward and his robot instantly revs its four offset wheels to follow it; he moves it closer and the robot leaps back, staying exactly 30 centimeters away from the book. Khammash weighs the machine down with his eyeglass case, he lifts the table at an angle, he replaces the wheels with ones that are 30% larger — each time, his robot restores its 30-centimeter buffer zone from the book and resumes staring at it.

The robot’s uncanny ability to correct its position gives it what biologists call robust perfect adaptation. “When the dust settles, there is no error,” said Khammash, a control theorist at the Swiss Federal Institute of Technology Zurich (ETH Zurich). “That’s the perfect adaptation; it keeps the distance perfectly.”

Whether in industrial control systems or in nature, negative feedback is an omnipresent strategy to help systems cope with disturbances. “People have noticed these feedback systems in physiology for as long as people have been studying physiology,” said Noah Olsman, a control theorist at Harvard University. Homeostasis, the self-regulation of biological systems, keeps many physiological parameters like body temperature, blood pressure and levels of blood glucose within exacting limits, whether we’ve run a marathon, gone scuba diving, or binge-watched Netflix all day. And for good reason: “If life couldn’t respond to changes and learn, it wouldn’t last very long,” Olsman said.

 

Continue reading at Quanta. Originally published on September 18, 2019.

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