The determination of the constant speed of light was a result of a series of experiments conducted in the late 19th and early 20th centuries. Here are some key experiments that contributed to this discovery:
Fizeau's Experiment (1849): This experiment involved directing light through a rapidly rotating cogwheel and reflecting it back from a distant mirror. By measuring the speed of light in the presence and absence of the rotating wheel, Fizeau attempted to detect any changes caused by the motion. Although Fizeau's experiment did not yield high accuracy, it provided early evidence that the speed of light might be independent of the source's motion.
Michelson-Morley Experiment (1887): This is one of the most famous experiments in the history of science. Albert A. Michelson and Edward W. Morley sought to detect the motion of the Earth through the hypothetical "ether" medium that was believed to permeate space. They used an interferometer to measure the speed of light in different directions at different times of the year when the Earth's velocity would change relative to the supposed ether. Surprisingly, the experiment showed no significant variation in the speed of light, regardless of the Earth's motion.
Einstein's Theory of Special Relativity (1905): Based on the results of previous experiments, Albert Einstein proposed his theory of special relativity. He postulated that the speed of light in a vacuum is an absolute constant and is the same for all observers, regardless of their relative motion. This theory introduced the famous equation E=mc² and revolutionized our understanding of space, time, and the behavior of light.
The accuracy of the constancy of the speed of light has been repeatedly confirmed through numerous subsequent experiments, including advanced interferometry techniques, measurements of the speed of light in different media, and studies of high-energy particle collisions. These experiments have consistently supported the notion that the speed of light in a vacuum is approximately 299,792,458 meters per second (or about 186,282 miles per second). The fundamental nature of light and its behavior in accordance with the principles of relativity have been confirmed with remarkable precision, providing a robust foundation for modern physics and technology.