A vehicle drives on the road being covering with water. Does it indicate that surface water is necessary for vehicle driving? I believe that everyone would give the answer “no”, for vehicles would drive smoothly without surface water on road. Vehicle driving does not need water as the medium. In the contrary, water would affect the driving speed of vehicle. If we assume the driving speed of vehicle is v0 when the water is static against the ground and the relative velocity of water against ground is x in the direction v0, then the driving speed of vehicle parallel to the flow direction is v0+x and the driving speed of vehicle against the flow direction is v0-x. Water flow affects the vehicle speed and the vehicle is seized by water.
A beam of light transmits in the air. Does it indicate that air is necessary for light? The answer is no. The transmission of light does not need the medium of air. In the same way, the existence of air would affect the velocity of light transmission. The velocity of light moving along the air is faster than that of light moving against the air. Light is seized by air. Compare the two scenarios above:
Vehicle……counterpart……light
Water……counterpart……air
Road……counterpart……ether
Water moves against road……counterpart……air moves against ether
Now let’s focus on light: (The velocity of light in the vacuum is C. Assuming air and ground are relatively static. x is the velocity component of ground against ether in the direction of light)
When the ground is static against ether, the velocity of light in the air is C0. Then it finds that the duration for light moving from A to B and from B to A is L/C0. When the velocity component of ground moving against ether is x, the duration moving from A to B is L/(C0+x-x) =L/C0 and the duration from B to A is L/(C0-x+x) =L/C0. Therefore, no matter what the x (the velocity component of ground against ether) it is, it would not affect the duration that light moves from A to B or from B to A. Therefore, such is the fundamental reason that Morley could not obverse the light interference fringe movement.
We improved Morley experiment and place the experiment in the vacuum environment completely. At this moment, light is not seized by air any more. The duration moving from A to B is L/(C-x) and the duration moving from B to A is L/(C+x). Such indicates that time needed varies with x.
Then let’s check the movement of the earth. The earth rotates around sun and also makes autorotation. Therefore, the velocity direction of earth revolution changes continuously against the velocity direction of light. That is, the component of velocity of earth revolution in the light direction keeps changing, which leads to the change of duration from A to B and from B to A. As a result, we could observe the movement of interference stripe through this improved Morley experiment. If it could find the movement, then it demonstrates that ether exists