I heard that there is now consensus in literature that a charged particle will take a DIFFERENT path around a neutral object than an uncharged particle. The reason is that the charged particle will radiate. I have even heard physicists try to wave this away as "well a charged particle needs to carry its "fields" around with it" so that is not a local object. If you take that stance, then the equivalence principle is completely worthless except for interactions which are purely point/contact interactions ... of which there are none. All four known fundemental forces can be described with fields. So what good is the equivalence principle? Alternative phrasing to make this more constructive: Can anyone completely mathematically/rigorously define the equivalence principle, and NOT have it be violated by the differring trajectories of a charged and neutral particle? EDIT: Just checked. According to the definitions in wikipedia, this would indeed violate the equivalence principle.