Benjamin B. Machta

A bacterium in a drop of water is looking for food. Around it, there's a chemical gradient: more food molecules on one side, fewer on the other. How should it move to reach the tasty spot fastest? It could steer smoothly, like a cyclist dodging a puddle. Or, like a bacterium, it could periodically stop, tumble, and swim off in a random direction.

Every 140 milliseconds, a small device connected to the car recorded speed, engine rpm, and coolant temperature. An ordinary Subaru was driving down the road, and its onboard computer turned into a measuring laboratory. That is how physicists set out to test how well a popular statistical measure reflects real energy expenditure. The measure is called entropy production.

A neuron perceives electrical signals like an ultrasensitive microphone picking up the faintest vibrations.