When the subway jerks, it is the distant stars that throw you down

Ideas & Philosophy · Published 3 October 2026 Swipe more like this →

In short: Philipp Frank, a key figure of the Vienna Circle, used this vivid image to explain the profound implications of Mach's Principle. A physicist and philosopher who fled Europe for Harvard, Frank spent his life bridging the gap between abstract scientific theory and the tangible reality of our physical universe.

Born in 1884, Philipp Frank was a central member of the logical positivist movement. After graduating from the University of Vienna in 1907 under Ludwig Boltzmann, he was recommended by Albert Einstein to lead the physics department at the German Charles-Ferdinand University in Prague. Frank held this prestigious professorship from 1912 until 1938, when the Nazi invasion of Czechoslovakia forced him to flee to the United States.

At Harvard, Frank became a vital link between European intellectual traditions and American academia. He founded the Institute for the Unity of Science in 1947, an organization that W.V. Quine famously described as a 'Vienna Circle in exile.' Frank was deeply concerned with the fragmentation of knowledge, a mission he pursued by teaching popular courses on the philosophy of science and writing extensively on the implications of relativity and quantum theory.

Frank is perhaps best remembered for his ability to distill complex physics into accessible, striking concepts. During World War II, he illustrated Mach's Principle—the idea that local inertia is determined by the distribution of mass in the universe—by pointing to a subway passenger losing their balance. He argued that the jerk of a subway car is not merely a local mechanical event, but a direct, instantaneous interaction between the rider and the distant stars. This interpretation highlighted a fundamental tension in modern physics: while Mach suggested an instantaneous connection, Einstein’s general relativity required that distant actions be retarded by the speed of light.

Throughout his career, Frank remained a dedicated socialist and a rigorous thinker who challenged the boundaries of causality. From his early days as a target of Lenin’s philosophical critiques to his later years as an influential Harvard lecturer, Frank remained committed to the idea that science and philosophy must be understood in tandem. He retired in 1954 and passed away in 1966, leaving behind a legacy of work that sought to unify the disparate branches of human inquiry.

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