The recent series of posts on Einstein's Special Theory of Relativity SR points to the fact that with the 2019 SI International Standard of Units, SR is no longer relevant, if it ever was. This should come as a relief to all students of physics.
In the 2019 SI Standard meter as the the unit of length is defined in terms of travel time of light assuming that the speed of light is exactly 299792458 meter/second, where second as the unit of time is determined by a standard caesium clock.
The SI Standard dictates that an observer X equipped with a Euclidean spatial $x$-axis must define distance along the $x$-axis by measuring travel time of light to different points along the axis using a standard caesium clock under the dictate that the speed of light is exactly 299792458 meter/second. In other words, the $x$-axis serves as an aether for the propagation of light with given standard speed.
Another observer X' equipped with an $x^\prime$-axis moving with constant velocity with respect to the $x$-axis (inertial motion), will have to follow the same SI Standard. The $x^\prime$-axis then serves as another aether for the propagation of light with given standard speed.
This means that under the SI Standard X and X' agree (have to accept) that the speed of light is exactly 299792458 meter/second. The $x$-axis and $x^\prime$-axis serve as different aethers for light propagation at standard speed.
In particular this means that the null result of the Michelson-Morley experiment is just what can be expected under the SI Standard. Each observer is connected to an individual aether which is "dragged along", and there are different aethers all with the same speed of light.
The real question is now:
- To what extent will X and X' be able to agree on distances and velocities? (Q)
This is the question addressed in
Many-Minds Relativity. The observers will not not agree on everything, and the extent depends what means of communication/physics are used. In particular they all use the same standard caesium clock with clock rate independent of inertial motion, thus without
time dilation.
The key point is that SR has nothing to say about (Q). This is because SR is based on a postulate (P) stating that the speed of light is the same for all observers. Einstein viewed this postulate to say something about how measures of space and time changes with observer motion leading to (strange) effects of time dilation and space contraction. But with the SI Standard (P) is simply a definition/prescription of how to measure space and time, which does not include anything of underlying physics. In short, (P) is empty of physics and so must SR be. The Lorentz transformation of SR does not describe physics.
SR has nothing to say about (Q) and so nothing to say after 2019. Since modern physics is based on SR, modern physics is not the same after 2019 and has to be rewritten into post-modern physics.
It is maybe ironic that SR by theoretical physicists worshipped as a fundamental element of modern physics, effectively was cancelled by modern experimental physicists forming the 2019 SI Standard for high-precision measurement of length/distance and time. This can be viewed as a form of self-correction of theory by observation, which is however not accepted by theoretical physicists who do not understand the practice of the 2019 SI Standard.This unfortunate situation is part of the crisis of modern physics with theory no longer in contact with observation.
Discussion is complicated since theoretical physicist do not care about/understand measuring technique, and experimental physicists do not care about/understand theory. My experience so far is that nobody is interested in a discussion about theory with observation and observation with theory, which after all is the objective of physics as science.
Recall that Einstein in 1905 used unspecified "meter sticks" and "clocks" in extreme "thought experiments" with human "observers" moving with speeds close to the speed of light, and so could draw sensational conclusions.
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