Equivalence Principle in EM theory?

[Alan Grayson]

I was watching a video in which the author was describing the difference between GR and EM theory, and she stated that EM has no Equivalence Principle. What would it mean if it did? TY, AG

[Brent Meeker]

There's no equivalence principle of EM because there are two different charges in EM so the reactions of charged bodies are not equivalent.  To wonder "What if it did?" is to ask what if there were only one sign of charge...it would be a completely different theory.

Brent

On 9/3/2024 1:32 AM, Alan Grayson wrote:

I was watching a video in which the author was describing the difference between GR and EM theory, and she stated that EM has no Equivalence Principle. What would it mean if it did? TY, AG --
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[Jesse Mazer]

What about in the classical Kaluza theory described at https://en.wikipedia.org/wiki/Kaluza–Klein_theory ? It seems from the description that it shows a way Maxwell's equations could be derived from spacetime curvature in the same way as gravity (albeit by adding an extra spatial dimension, which Klein postulated might be rolled up), I wonder how it accounts for positive vs. negative charge and if there is still an equivalence principle where it approaches Minkowski spacetime in the small-scale limit.

Jesse

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[Alan Grayson]

If an EP for E&M existed, what would it say which could be falsified? AG

[Alan Grayson]

I am not clear why the opposite charges of E&M, defeats the possibility of an EP for that theory. AG

[Brent Meeker]

It's already falsified because if you give a geometric interpretation to the motion of positive charges then negative charge motion violates the geometric interpretation and they both violate the geometric interpretation of gravity.

Brent

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[Alan Grayson]

In GR, the EP says that gravity is equivalent to acceleration (when ignoring tidal forces), but hypothetically, if there's some EP for E&M, what would be equivalent to what? AG