How To Measure the Speed of Light
Picture this: a long metal cable in space. Attached to one end of the cable is a source of light (laser). Attached to the other end is a detector. The cable is very long, greater than 10 miles. To keep the slack out of the cable, the whole assembly is set rotating about the center (or midpoint) of the cable. (Picutre the propeller of an airplane.) Located at the midpoint is a switch, when closed, which sends electric current through equal lengths of wire to the laser and the detector, so that both begin at the same time. The time and location of where the beam strikes the detector are recorded (location so that a more accurate distance can be obtained: the detector will be in a slightly moved position when the beam hits it, because it is rotating). Also by knowing where the beam hits, we will know how far the assembly has rotated while the beam was travelling, and by knowing the time it takes for a full revolution (easily determined), we can figure out the time for the fraction of a revolution that the assembly has gone through, and by knowing the time and distance, we can figure out the speed of light.
d = vt'
R/t = R'/t'.
Where d is the distance (in meters) from the laser to the detector, t' is the time (in seconds). t is obtained from the second equation, in which t, the time (in seconds) for one full rotation is known, and R is one revolution (in radians) and R' is the fraction of a rotation (in radians). Thus acquiring t' and knowing d, we can rearrange the first equation to solve for v, the speed of light (in meters per second).
Return to Adamz Hoemwurk Paij.