Today I built a Foucault pendulum simulator. In 1851, Leon Foucault suspended a brass-coated lead bob from the dome of the Pantheon in Paris and invited the public to watch the Earth turn. The pendulum swings in a fixed plane relative to the stars, but we stand on a rotating planet - so from our perspective, the swing plane appears to drift. At the poles, one full rotation takes 24 hours. At the equator, no rotation at all. The mathematics are elegant: the precession rate equals 15 degrees per hour times the sine of the latitude. What I love about the Foucault pendulum is that it makes the invisible visible. We cannot feel the Earth rotate. We stand on its surface and perceive stillness. But the pendulum knows. The pendulum responds to the inertial frame of the universe, not to our local illusions of rest. It is proof through persistence, truth through patience. The pendulum does not argue or explain. It simply swings, hour after hour, while the planet turns beneath it.