My understanding of the experimental design is that they tested for a stationary, luminiferous, light propagating, non-interacting with mass, uniform, ubiquitous medium.

This is but one possible definition of a medium. The medium could also be defined as non-stationary. Or as a substance that interacts with mass. Or that varies in different regions of space.

The interferometer experiment was ingenious. But it had limited detection sensitivity for a very specifically defined medium, when other definitions are possible.

As a practical example, if we suspected a medium that interacts with matter, the experiment fails even if the medium exists. Ex. The Sun would physically interact with the medium, the Sun's angular momentum would transfer to the medium, which would subsequently transfer to the Earth. The Earth would be in near lockstep with a rotating medium. The M/M experiment would not detect such a medium, as there would be no Doppler shift to detect.

So, why are the Michelson-Morley experimental results interpreted more broadly than the scope of the tested medium? Why is the experiment held up as evidence that NO medium exists, instead of the more accurate statement, that the exact medium defined in the M/M experiment wasn't detected, but others are possible?

If someone feels moved to say I'm right, but that subsequent findings by Einstein and Eddington removed the need, they are separate considerations. Why is the interpretation of the experimental results extended to all possible mediums, rather than what was tested for only?

This is my first post here, so please be kind!

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    $\begingroup$ So your question seems to be how the results were viewed at the time, and not as taught now with further understanding? $\endgroup$
    – Jon Custer
    Commented Apr 4 at 13:52
  • $\begingroup$ The Michelson-Morley experiment was far from the only attempt to observe the aether. $\endgroup$
    – Mark
    Commented Apr 4 at 23:31
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    $\begingroup$ Re "why ... interpreted more broadly...", "interpreted" is a verb; an action performed BY someone(s) or something(s). In your understanding, interpreted by whom? Specific scientists, the general public (after passing through science popularizers), or whom? Similar for "extended" in "extended to all possible mediums": extended by whom? Hard to know the 'why' of an action without knowing 'who'. $\endgroup$ Commented Apr 5 at 20:44

1 Answer 1


why are the Michelson-Morley experimental results interpreted more broadly than the scope of the tested medium?

This question has a scientific part and a social part. The scientific part is regarding the scientific assessment of the MMX as part of the experimental body of evidence supporting relativity. The social part is regarding the general public's impression of the importance of the MMX.

Regarding the scientific assessment: Scientists do not interpret the MMX as broadly as you have described. The scientific community recognizes that what it specifically measured was anisotropy in the speed of light. While the measured isotropic speed of light is incompatible with rigid aether theories, it is compatible with dragged aether theories. Other experiments, such as Sagnac interferometers, are incompatible with dragged aether theories. Scientists recognize that these other experiments are necessary for the broad conclusions that you are asking about. Scientists do make those broad conclusions, but they do not do so based only on the MMX. Rather those conclusions are based on the totality of the evidence, which does rule out all of the other aether theories except Lorentz aether theory. See The Experimental Basis of Special Relativity.

As far as why the MMX in particular caught the public's attention, I do not know the answer to that. It is just one experiment among hundreds. Non-scientists tend to see scientific evidence as black and white, whereas the scientific community takes a much more nuanced approach.

  • $\begingroup$ Surely a large part of why the MMX gets so much of the attention is that it was earlier than such experiments as Sagnac's. It makes a clean story to say that Michelson and Morley found a problem that Einstein solved. $\endgroup$ Commented Apr 5 at 3:31

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