8.2   MICHELSON-MORLEY EXPERIMENT

In that years many Physicians believed that the light should move in a particular medium in the space called the ether.

The experiment was conceived to detect any variation of light velocity in the possible moving ether. A negative result was obtained and was proved that the ether does not exist.

We will see here how the Emission Theory is consistent with the Michelson-Morley experiment.

The Michelson-Morley apparatus consist of a source of light and a special disposition of mirrors as shown in the figure.

 The central mirror is only partial reflective so that part of the beam is reflected but part of it passes through. The other mirrors are totally reflective. Then a beam of light is divided into two beams by the central mirror. Each one is reflected in a different mirror and they both come back to the central one. The beams are partially reflected again and they finally join and a composed beam reaches the interference detector. The total apparatus moves with Earth. Then the source, the mirrors and the detectors all have a velocity u. If a difference in the relative velocity of the beams respect to the mirrors exists in one path a phase difference would be observed in the phase detector.

The Emission theory states that the light has a velocity vector ç that is the vector addition of the constant velocity vector c in the direction of the emitted beam and the source velocity vector u.

ç = c + u

When a beam of light is reflected by or passes through a mirror it interacts with in such a way that the mirrors act as a new source for the beams. This means that the light wins a new velocity vector each time a beam interact with a mirror as shown in the figure.

Respect to the mirrors all of the beams have the same relative velocity.

In other way, calculations of the absolute velocities can be made to show that the two final beams reach the detector in phase. Then no phase difference is theoretically expected.