Offline fisherman

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The equivalence principle and non-uniform motion
« on: April 19, 2021, 07:29:56 PM »
UA starts with the EP as its foundation as a theory for gravity.  Uniformly accelerated motion is the equivalent of being at rest in a gravitational field, therefore it follows that what we experience as gravity is actually the uniform acceleration of the earth. (Please correct if I have misrepresented)

But why can they be considered equivalent?  Because the situations are symmetrical. In both cases, the observer experiences the same forces (or lack of them).  But non-uniform motion is not the equivalent of being at rest in a gravitational field. The forces experienced by an observer in uniform motion are not the same as the forces experienced by an observer in non-uniform motion.

I think that is where using the EP, in isolation, as a foundation for a theory of gravity breaks down.  It doesn’t explain how gravity works with respect to non-uniform motion.  As long as it is limited to objects that “are at rest in a gravitational” field it works fine, but it doesn’t explain how gravity works with respect to objects that are not at rest in a gravitational field.