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How do other forces, like E&M fit in to GR?
...Imagine the earth having aAccording to GR the inertial frame is still the freefall frame and the
net charge, and a person having enough charge that electrostatics
exactly counterbalance gravity (and ignore rotation). Is the "inertial
frame" still the one accelerating downward at -9.8 m/s due to curved
space time, or is it the one with no acceleration.
If you choose the first, it would seem you need to talk about THREE
fundamental forces, and a "fundamental curver of spacetime."
If you choose the second, then all four force are on an even status:
either as "forces" or as "curvers of spacetime."
If we want to interpret gravity as "curving spacetime" instead of as a
"force", that would be fine. Both give the same motion, which
is the ultimate test. It is just a question of a MODEL not a
question of the PHYSICS.
But then why not choose a model so that the
other three forces "curve spacetime" as well?
Or put another way, why is the "intertial frame" the one where only
GRAVITY is acting? Why not the one where only E&M is acting, or only
the strong force is acting?
To me, putting all four forces on the same level is simpler and more
appealing. Of course, experiment, not "appeal" is the final arbitrator.
Can experiment point to a fundamental difference between gravity and
other forces that justifies giving it this special status?