[n4r9]

I'm probably missing some of the nuances, but I'm referring generally to the Equivalence Principle, described by Einstein as:

> we ... assume the complete physical equivalence of a gravitational field and a corresponding acceleration of the reference system

[codethief]

I see. Personally, the way I have always interpreted that quote is that here, in this particular case, "gravitational field" is supposed to mean "someone standing on the surface of Earth, experiencing gravity" or, more generally, "an observer in a spacetime who's not in free fall / not moving along a geodesic" (but e.g. standing on the surface of a massive body).

Otherwise, as outlined in my previous comment, it does not make any sense.