The fact is, either approach is correct and one does not preclude the other. Yes, the Principle of Relativity is elegant and the top-down approach is easier to use; physicists love it for that reason. But the field equations are also elegant and they not only contain the Principle of Relativity within them, they also provide a physical explanation for effects that otherwise are paradoxical. We can never know if God started with the Principle of Relativity and derived the field equations or started with the field equations from which follows the Principle.
( Rodney A. Brooks )
[ Fields of Color: The theory ]
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