For this, we would have to measure the speed of light from point A to point B, rather than for the round trip.

The one-way speed of light is the speed of light in one direction. This is the only speed of light that has been measured by anyone to date. The round trip speed of light is also called the two-way speed of light. The speed of light is taken as the average of the speed of light as it travels from A to B, and its consequent speed as it travels from B to A. That is, measurements are of the time taken for a round trip. We are measuring the time it takes to go from point A to point B and then reflect back to point A. In such a case, we are not measuring the time that light takes to go from point A to point B. If we know the distance between the source and the mirror, and we measure the time it takes for a beam or pulse of light to be reflected back, we can easily calculate the speed of light from there. (Photo Credit : Wikimedia commons)Įssentially, we need a source of light, a mirror, and a timer. Experimental setup employed by Fizeau to measure the speed of light.

What is the speed of light