The Michelson-Morley experiment null result did not agree with prediction so it was concluded the Aether did not exist. But the prediction was not based on correct theory. Aether theory does predict the null result. No local experiment can directly detect or deny the existence of the Aether.
Why the experiment was made.
Prior to 1887 the physics community accepted, almost to a man, that Space was a special substance called the Aether. They reasoned that the Aether hypothesis explained many otherwise unanswered questions. It was therefore determined to prove or disprove the hypothesis by experiment.
Two Americans, Albert Michelson and Edward Morley, designed an experiment to measure the Earth's velocity through the Aether. A positive Aether velocity would prove the existence of the Aether.
The Michelson-Morley apparatus
The Aether hypothesis states that the speed of light is determined by the propagation velocity of the Aether substance. Hence it is constant in all directions. Therefore, the speed of light relative to the Michelson-Morley apparatus would not be constant with direction if the apparatus moved through the Aether.
Michelson and Morley's idea was to measure the one way speed of light, relative to the apparatus, in all directions in Space. Light approaching from the point in Space to which the Earth is moving would be measured to be a c + v and, in the opposite direction, c - v. The difference between these velocities, divided by two, gives the Aether velocity of the apparatus.
However, it is a fact that the one way speed of light cannot be measured due to limitations in timing the passage of light over a set distance. Thus the Michelson-Morley apparatus actually measured the two way, out and return, average velocity. But the two way speed of light is identical in opposite directions. However, it was calculated that a difference existed between directions at 90degs to each other. This difference was of the second rather than the first order and was therefore very small. Nevertheless it was expected to be measurable by the apparatus.
The Michelson-Morley apparatus consisted of two equal length arms at 90degs to each other joined at their ends by connection to a beam-splitter. In essence a light pulse is fed into the beam-splitter which directs each half of the pulse along the two arms to be reflected back to the beam-splitter from mirrors situated at the far ends. The time difference in the arrival of the two returning light pulses is determined by measuring the shift in the interference fringes of the combined beams. Thus the difference in the average speed of light in directions at 90 degs to each other can be determined.However the experiment observed no difference for any direction in Space.
There are four possible reasons for this null result.
- The Earth is stationary in the Aether.
- The Aether does not exist.
- It is not possible to detect Aether velocity.
- The whole experiment is misconceived.
It is most unlikely that the Earth, amongst all the billions of cosmic bodies in the Universe, happens to be the one body to be stationary. If any body in our solar system were stationary it would be expected to be the Sun. The Earth would then move through the Aether at its solar orbital speed of 30km/s.
So, is it possible to detect the Aether velocity of a body; and if not why not. But first of all:-
The experiment is misconceived
It is essential in all experiments that theory is applied to predict and explain the result. If the prediction matches the actual observation the applied theory is correct (at least for that experiment).Now the Michelson-Morley experiment is an experiment of the Aether - hence Aether theory should be employed for the prediction of the result. However, instead, the experimenters applied non-Aether theory (understandable as they knew no Aether theory). Naturally their prediction disagreed with the observation.
But if the experimenters had known Aether theory and applied it what would have been the point? For the existance of a viable Aether physics proves, in itself, that the Aether does exist.
Thus there is no need for the Michelson-Morley experiment or indeed for any experiment designed to prove or disprove the existance of the Aether.
The effect of Aether theory on the Michelson-Morley apparatus
Aether theory dictates that matter length contracts in the direction of its Aether velocity according to the inverse of the Lorentz factor. This effect is commonly called the Fitzgerald-Lorentz contraction effect. Secondly Aether theory dictates that matter Time (matter Time is a little different to Space Time) dilates as a function of the Lorentz factor. The Lorentz factor is 1/sqrt(1 - v2/c2). These effects are derived from a consideration of the electric field which in turn derives from the properties of the Aether. The effects and origin are explained in the paper The Electric Field in Aether Physics.
An examination of the length of the light paths along the two equal length arms of the MM apparatus discloses that the light path along the arm in line with Aether velocity is longer than the light path of the other arm. However, applying Aether theory, the apparatus arm in line with Aether velocity contracts in length while the other arm contracts only in width. This relative shortening of the inline arm exactly cancels the longer light path such that the light paths along the two arms are always exactly equal whatever the Aether velocity - thus giving the observed null result.
Time dilation does not affect the Michelson-Morley experiment but it does effect a modified version called the Kennedy-Thorndike experiment. Taking both effects into account gives a prediction of the observed null result.
If these two Aether velocity effects (and their derivatives) are applied to the prediction of the result of ANY experiment designed to measure or detect Aether velocity it will be discovered that they all give a null result.