I think that this post deserves a thread, to analyze it deeper.

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1) In 1945, Isidor Rabi first publicly suggested that atomic beam magnetic
resonance might be used as the basis of a clock.

2) First functional atomic clock: It was an ammonia absorption line device
at 23870.1 MHz built in 1949 at the U.S. National Bureau of Standards
(NBS, now NIST). It was less accurate than existing quartz clocks, but
served to demonstrate the concept.

3) In 1955 Louis Essen and Jack Parry produced the first practical cesium
atomic frequency standard.

Einstein, with help of friends at Berlin and Princeton, invested 30+ years
of his late life trying to unify gravitational theory with QM theories.

And yet, not one single scientist between 1913 and 1975 questioned
the influence of gravity on emission of spectral lines? Maybe, between
1925 and 1945, the physics community wasn't exactly aware of
hyperfine transitions. After all, they had enough problems with fine
transitions that plagued the QM world, and make Schrodinger to
abandon his own work by mid 1930's, tired of such occurrences.

But there is no excuse, since 1945, for any physicist for not having
thinking about atomic clocks and height, in particular after 30 years
of General Relativity being around.

After all, since 1907, Einstein anticipated Gravitational time dilation, as
a consequence of special relativity in accelerated frames of reference.

So, where is the truth on this GNSS(GPS, GLONASS, Galileo, etc.)
problem with relativity? True or false?