Not that it's all that relevant to this discussion, but this is a controversial claim that Einstein himself later appeared to reject. Many theorists argue that GR does not, and cannot, "reduce to SR."
See, for example:
The relationship between special relativity and gravitational theory has never been entirely straightforward. After designing the 1916 general theory of relativity to reduce to the existing 1905 “special” theory as a limiting case, Einstein wrote in 1950 that he no longer believed this approach to be legitimate.
And in 1960 we discovered a fundamental geometrical conflict between special relativity and the general principle of relativity applied to rotation, the community's response being to give SR priority, and downgrade the GPoR from a rule to a guideline that was to be suspended whenever it threatened to disagree with SR-based arguments. We then found in the 1970s that the resulting SR-centric theory refused to mesh with quantum mechanics and with basic statistical laws, apparently as a result of the SR component.
To these difficulties we will now add an even more fundamental problem:....At this point, the only remaining defence of special relativity would seem to be that if these GEM effects really are incompatible with SR, then since SR cannot be wrong, the effects cannot exist, on principle. This is perhaps more of a defensive “theological” position than an investigative and scientifically-minded one....
In conclusion: A fully-functional general theory of relativity, or any other fully consistent gravitational model, cannot and should not include a reduction to the flat-spacetime equations of the 1905 theory.
"This is perhaps more of a defensive “theological” position than an investigative and scientifically-minded one." Perhaps? Well, I guess that's a polite way of putting it, eh?
Edited by Moronium, 03 February 2019 - 11:22 PM.