I don't agree with this characterization. This is not to say that foundational studies are never invalidated: I just don't think MM was one of them.
> Michelson-Morley experiment found no changes in speed of light at all. Nothing. Zero fluctuations.
The MM experiment aimed to observe a predicted effect of the theory of luminiferous aether, which would have enabled measuring the Earth's speed relative to a canonical reference frame (the aether). It was sufficiently precise to observe that predicted effect but did not observe it, which provided strong evidence that the aether theory was wrong.
Finding that any variation in the propagation of light was too small to be detected by their instruments (and too small to be consistent with aether theory) is not the same as finding that it's exactly zero.
> These fluctuations of speed of light were found much later, by LIGO/VIRGO and NANOGrav.
It's not the same fluctuations though: these experiments found much smaller fluctuations than MM looked for, from a different effect. They're not even (understood to be) fluctuations in c, but in the shape of space.
> The flaw of Michelson-Morley experiment is that it was performed in isolated environment, but tried to measure an external effect.
The later interferometer experiments (LIGO and VIRGO) are conceptually very similar to the original MM experiment. The environment is not fundamentally different, and on the contrary LIGO and VIRGO are better isolated (against ordinary vibrations: we don't know any way to isolate an experiment from gravitational waves). They're just much larger and more precise, which is why they can observe the much smaller effect of gravitational waves.
> However, Michelson-Morley experiment is one of corner stones for theory of Relativity.
Yes, but the effects observed by LIGO and VIRGO are predicted by general relativity, which is what inspired scientists to carry out those experiments. As far as I know, they are consistent with GR to the extent that LIGO and VIRGO have measured them.
> The MM experiment aimed to observe a predicted effect of the theory of luminiferous aether ... which provided strong evidence that the aether theory was wrong.
MM failed to observe effects predicted by theory of STATIC luminiferous aether. It looks like there is no absolute aether frame (which will be strange to have in the infinite Universe).
> They're just much larger and more precise, which is why they can observe the much smaller effect of gravitational waves.
Yep. We can discard MM experiment now, because LIGO/Virgo is much better.
If we want to measure wind at high altitude, but we put our measurement tool deep and isolated it well, with high enough precision, we will be able to measure distant earthquakes and nuclear explosions. No luck with wind, of course.
To catch the wind, we need something like NANOgrav, but at much smaller scale at high orbit around Earth. Luckily, we have large number of GPS satellites with high-precision clocks in the sky: https://link.springer.com/article/10.1007/s10291-017-0686-6 . I see strong annual signal here.
> Yes, but the effects observed by LIGO and VIRGO are predicted by general relativity
This doesn't make GR unique. Other theories can predict this too. It's just waves in a medium. However, GR is abstract theory, which lacks explanation power. Lack of explanation causes lack of understanding.
> Michelson-Morley experiment found no changes in speed of light at all. Nothing. Zero fluctuations.
The MM experiment aimed to observe a predicted effect of the theory of luminiferous aether, which would have enabled measuring the Earth's speed relative to a canonical reference frame (the aether). It was sufficiently precise to observe that predicted effect but did not observe it, which provided strong evidence that the aether theory was wrong.
Finding that any variation in the propagation of light was too small to be detected by their instruments (and too small to be consistent with aether theory) is not the same as finding that it's exactly zero.
> These fluctuations of speed of light were found much later, by LIGO/VIRGO and NANOGrav.
It's not the same fluctuations though: these experiments found much smaller fluctuations than MM looked for, from a different effect. They're not even (understood to be) fluctuations in c, but in the shape of space.
> The flaw of Michelson-Morley experiment is that it was performed in isolated environment, but tried to measure an external effect.
The later interferometer experiments (LIGO and VIRGO) are conceptually very similar to the original MM experiment. The environment is not fundamentally different, and on the contrary LIGO and VIRGO are better isolated (against ordinary vibrations: we don't know any way to isolate an experiment from gravitational waves). They're just much larger and more precise, which is why they can observe the much smaller effect of gravitational waves.
> However, Michelson-Morley experiment is one of corner stones for theory of Relativity.
Yes, but the effects observed by LIGO and VIRGO are predicted by general relativity, which is what inspired scientists to carry out those experiments. As far as I know, they are consistent with GR to the extent that LIGO and VIRGO have measured them.