André Assis and Alexander Unzicker Discuss Mach's Principle

I just listened for the second time to a very interesting interview that Dr. Alexander Unzicker, who runs the Unzicker’s Real Physics YouTube channel, conducted with Prof. André Koch Torres Assis, on the topic of Mach’s Principle.

During this interview, André Assis explains the idea of Mach’s principle. Ernst Mach (1838-1916) was an Austrian physicist who criticized Isaac Newton’s use of absolute space in his Principia, and who argued that the phenomena of inertia and gravity that Newton wrote about should be made with respect to the remainder of the matter in the universe (the fixed stars, etc.), rather than to absolute, empty space.

This question is most easily expressed with Newton’s bucket experiment. A bucket partially filled with water is hung from a string, the string is wound up, and then the bucket is allowed to spin. The water will rise up on the sides on the bucket, and the surface of the water will form a parabola. The question is, why is the water rising up? Newton’s answer was with respect to absolute space, while Mach claimed it was with respect to the rest of the universe.

The interview covers a number of different topics, including Newton’s bucket experiment, the gravitational pull of the earth and the nature of the universal gravitational constant G, the flattening of the earth because of its rotation, and Foucault’s pendulum. For each of these, the Newtonian and Machian perspectives give different results. It is also interesting that notwithstanding the fact that Einstein was influenced by Mach, Einstein’s general relativity does not respect Mach’s principle anymore than does Newton’s gravity.

I encourage everyone to watch the video. It is easy to follow and absolutely fascinating to listen to.

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