Why does the Michelson-Morley experiment only contradict the aether? This question is related to Validity of Maxwell's equations with no aether or relativity? (so please read this first). In this question, the answers seem to suggest that getting rid of the aether was not a problem (in the sense that we don't need to throw away Newton's equations) and that there could be other special frames where Maxwell's equations hold in their 'nice' form (and not in their nice form in other frames). I have two further questions:


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*Why does the Michelson-Morley experiment only contradict the aether and not all special frames? From what I have read of the experiment, it would seem to me to suggest that it does indeed contradict all special frames and therefore that they should have concluded that there are no special frames not just that there is no aether.

*What forms other than the aether could these special frames take?
 A: There is an alternate formulation to special relativity, Lorentz Ether Theory. This alternate theory allows the ether frame to still exist. Nobody teaches it. Why?
Special relativity makes two very simple assumptions, that the laws of physics are the same in all inertial frames, and that the speed of light is the same to all inertial observers. The Lorentz transformation and everything implied by it follow from these simple assumptions.
Lorentz Ether Theory on the other hand posits a special frame, the ether frame, where Maxwell's laws truly do hold. Per this theory, this is the only frame in which the one-way speed of light is Maxwell's c. Lorentz Ether Theory also posits time dilation and length contraction as axiomatic. These lead to the Lorentz transformation, and to the round trip speed of light being Maxwell's c.
The only way to distinguish these two theories is to find a way to measure the one-way speed of light. That's not possible, and thus there is no way to experimentally distinguish the two theories. Yet physics instructors only teach special relativity. You have to dig deep, very deep, to find proponents of Lorentz Ether Theory.
One reason is that the assumptions of time dilation and length contraction as axiomatic seem rather ad hoc (and that's putting it nicely). An even bigger reason is that Lorentz Ether Theory introduces a key untestable hypothesis, the existence of the ether frame. This frame cannot be detected. Time dilation and length contraction conspire to hide it from view. A bigger reason yet is general relativity. The axioms of Lorentz Ether Theory are inconsistent with general relativity. The final nail in the coffin is quantum mechanics, which eliminates the need for a medium through which light propagates. Without that very self-contradictory medium (the luminiferous aether), what's the point of having an ether frame?

The modern geometrical perspective of special relativity isn't so much that the speed of light is constant but rather that there exists some finite speed that is the same to all observers, and that light necessarily moves at this speed because it is carried by massless particles.
What motivates the existence of this finite universally agreed upon speed is geometry. What geometries yield a universe in which Newtonian mechanics appears to hold in the limit of zero velocity, and what do these geometries say about a speed that is the same to all observers?
The answer is that there are two cases: This universally agreed upon speed is infinite or finite. An infinite universally agreed upon speed results in Newton's universe. A finite speed results in Minkowski space-time describing the geometry of special relativity. Experimentally, the finite speed of light appears to be the same to all observers, thus falsifying the notion of a Newtonian universe with Euclidean space and time as the independent variable.
A: The Michelson-Morley result is a challenge to any theory which specifies a preferred frame for electromagnetism and this is why it causes problems for aether theory. I don't think the answers to your previous question imply anything else. The problem of finding the correct reference frame for electromagnetism was solved, not by finding a preferred frame, but by finding a different set of rules for transforming between frames so that it was correct in every frame. 
A: my opinion for why M-M refutes aether is that "special frames" fails either Occam's Razor or the Copernican Principle.
if there was truly aether in existence and the M-M results valid, that would mean that this "special frame" moves along with the Earth around the sun all of the time.  the reason why the M-M results spoke so significantly was that they ran the experiment over and over again during multiple seasons of the year.  if the Earth is not particularly special as a place in the Universe (let's set aside that the "special frame" moves around with these "special" intelligent life forms called "homo sapiens"), we must expect that while it's possible that in the spring the Earth just happens to move along with the aether, then in the autumn in must be moving through it.  and fast enough that the shift in the interference pattern in M-M would be clearly noticeable.  but no such shift ever happened.
unlike string theory (or a conjecture of the Multiverse), the aether theory was actually falsifiable.  it made a prediction that could eventually be tested, it was tested in 1887 was falsified.  something should have been noticed unless you claim that the aether follows our planet around as we go around the Sun.
A: ...the properties of this so called aether, was meant to have zero shear and be like an idealistic medium that could not be disfigured by any known force. then how could we expect the MM experiment to have a phase lag. Aether may be non-existent but we don't know that through this experiment. Moreover, the space-time fabric is getting thicker and more relevant and could be another name for aether. So the existence of an all pervasive medium seems plausible and required.
