gr01 The grains of coffee closer to the earth accelerate towards it a bit more, causing the ball to start stretching in the vertical direction. However, as the grains all accelerate towards the center of the earth, the ball also starts being squashed in the two horizontal directions. Einstein’s equation says that if we treat the coffee grains as test particles, these two effects cancel each other when we calculate the second derivative of the ball’s volume, leaving us with ¨ V |t=0 = 0. It is a fun exercise to check this using Newton’s theory of gravity!

The grains of coffee closer to the earth accelerate towards it a bit more, causing the ball to start stretching in the vertical direction. However, as the grains all accelerate towards the center of the earth, the ball also starts being squashed in the two horizontal directions. Einstein’s equation says that if we treat the coffee grains as test particles, these two effects cancel each other when we calculate the second derivative of the ball’s volume, leaving us with ¨ V |t=0 = 0. It is a fun exercise to check this using Newton’s theory of gravity!

[PDF]The Meaning of Einstein's Equation

web.stanford.edu/~oas/SI/.../lib/BaezEinsteinEqn.pdf

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by JC Baez - ‎2001 - ‎Cited by 29 - ‎Related articles

Mar 10, 2001 - The Meaning of Einstein's Equation. John C. Baez. Department of Mathematics, University of California. Riverside, California 92521. USA.