Yes, the speed of light has been measured experimentally. The currently accepted value for the speed of light in a vacuum is approximately 299,792,458 meters per second, denoted as "c" in scientific equations. This value is defined as a fundamental constant in physics.
One of the earliest successful experiments to measure the speed of light was conducted by Ole Rømer in the late 17th century. Rømer observed the variations in the timing of the eclipses of Jupiter's moon, Io, as the Earth moved closer to or farther away from Jupiter in its orbit around the Sun. By analyzing the time differences, Rømer estimated the speed of light to be finite and not infinite as previously believed.
Over the centuries, more accurate and refined methods have been developed to measure the speed of light. Techniques such as using rotating mirrors, interference patterns, and precise timing methods have been employed in experiments.
Today, one of the most accurate methods involves using lasers and sophisticated timing equipment. For example, the speed of light can be measured by sending laser pulses over a known distance and precisely measuring the time it takes for the light to travel.
These experimental measurements, combined with theoretical developments in the field of electromagnetism, have led to the determination of the speed of light as a fundamental constant in physics.