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[asterroc]

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[q10.livejournal.com]

you're right, of course, that i was mixing things up and/or being sloppy.

i was mainly remembering being taught to think of an elevator in free-fall as a canonical inertial frame, which is, i'm sure, wrong in the details, but which is really good enough a lot of the time.

[sildra.livejournal.com]

Well, it is true that if you decide to invoke curvature of spacetime rather than gravity, you can redefine inertial to mean anything moving along a geodesic in your curved spacetime, and it won't contradict the Special Relativity definition of inertial (just expand on it). In that case, an elevator in free-fall is an inertial frame, yes. It's an either-or thing, though. If you call it "gravity" instead, then it's an accelerating frame, which is not inertial. But the basic argument in favor of General Relativity (ignoring, of course, that now that the framework has been built up, GR was shown to predict new phenomena which have since been discovered) is that an object in freefall looks, in a lot of ways, more like an object in an inertial frame than like an object with a force applied to it.