Null Result of Michelson-Morley Experiment vs 2019 SI Meter Standard

This is a further clarification of the recent posts on the 2019 SI definition of length scale.

Einstein's Special Theory of Relativity SR as a pillar of modern physics came out from an effort to explain the Michelson-Morley experiment performed in 1887 with the objective of detecting the presence of a luminiferous aether as a medium surrounding the Earth carrying light waves. The MM-experiment gave a null result (as the most famous "failed experiment") indicating that if there was such a medium, then it must be "dragged along" by the Earth, which was viewed to be very strange. I will return to this below.

More generally, the null result indicated that the speed of light is the same independent of motion with constant velocity, so called inertial motion.  

To maintain credibility, the physics community was in desperate need to explain the MM null result and to this end the FitzGerald–Lorentz length contraction hypothesis was fabricated suggesting a change of spatial scale depending on motion, but that was also viewed as very strange. How could the lenght of a solid bar change with inertial motion. 

Then came Einstein with his SR in 1905 claiming that there is no medium at all required for propagation of light, thus explaining the MM null result from null presence of any medium as a very radical solution as a form of null from null. 

But the physics community did not accept SR until much later long after Einstein himself had distanced himself from SR as being null. What opened physics books to SR was Einstein's General Theory of Relativity GR from 1916 kick-started in 1919 as supposedly experimentally verified by Eddington's solar eclipse experiment.  

The net result is that modern physics is based on SR/GR and quantum mechanics, with a declared formidable success however compromised by the fact that these two theories are incompatible. This ended in a stalemate with no hope to finding a common theory. The result is that modern physics today is in a state of crisis from unresolved incompatibilities.

But in 2019 a new element was brought in by the International Committee for Weights and Measurements (CIPM) setting a new standard for length scale (meter) defined by travel time of light defining the speed of light (in vacuum) to be exactly 299792458 meter per second with time measured by a standard caesium atomic clock. 

This means that since 2019 the length scale for a given inertial Euclidean coordinate system $X$ traveling with a constant velocity with respect to other inertial systems, is determined by sending a light signal from the origin of $X$ and marking distance along coordinate axes by travel time of light assuming a specific speed of light. This means that effectively each inertial coordinate system $X$ serves as a medium for propagation of light at a specific speed, as if the medium is dragged along with the coordinate system. Since there are many different inertial systems,there are many media for light propagation each one at rest with its inertial system. 

This opens to a different explanation of the MM null result than that of Einstein with no medium, as a many-media situation (as suggested already by Ebenezer Cunningham in the 1910s) elaborated as Many-Minds Relativity. 

The MM null result is then explained by the fact that the length scale in each inertial system $X$ is established by travel time of light assuming that it propagates at exactly 299792458 meter per second in $X$. This means that the length scale depends on motion, and the issue is then to assess difference in distance measurements in different inertial systems, which is the topic of Many-Minds Relativity. 

The length scale thus depends on motion, but it does not mean that a solid bar is affected in any way by inertial motion. The bar remains the same but its length changes because length scale changes.  

In orther words, modern physics has since 2019 returned to a pre-SR era with each inertial system "dragging along" its own medium for light propagation, thus elimination the mission of SR. 

The MM null result is thus finally explained in terms of inertial systems"dragging along" media for light propagation, along the original Lorentz idea.