Fizeau experiment

The Fizeau experiment, conducted by Hippolyte Fizeau in 1849, measured how fast light travels. He used a rotating wheel with teeth, shining a beam of light through the gaps toward a mirror several kilometers away. When the wheel's speed was just right, the light was blocked or allowed through, depending on the rotation, revealing the time it takes for light to travel back and forth. This experiment provided one of the first direct measurements of light's finite speed, confirming that light does not travel instantaneously but at a consistent and measurable velocity.