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- TL;DR Summary
- Does relativity theory necessarily disallow all physical effects that may be termed "instant"?

I guess it is safe to say that SR is, mathematically speaking, a framework that correlates discrete events in spacetime by way of a universal constant (the speed of light) so that the "proper distances" that separate them may be determined. I think this means that every conceivable "instant effect" is disqualified under this framework. Every physical "happening" in SR, in other words, would always depend on the logic of mediating influences between isolated point-like events.

But I don't see that this is necessarily the case under the framework of GR. I always hear popularizers affirming the idea that the theory of relativity disallows every "action at a distance". When it comes to "actions" related to physical effects that require the introduction of traveling electromagnetic disturbances, that is quite sensible.

But this doesn't mean that every conceivable physical effect — considered under the framework of GR — absolutely requires a mediating signal, right?

An obvious example is the application of the mathematics of GR to the physics of gravitation. It should be safe to admit that not every gravitational model developed under GR is

I think the technical way of asking this is: Does GR

But I don't see that this is necessarily the case under the framework of GR. I always hear popularizers affirming the idea that the theory of relativity disallows every "action at a distance". When it comes to "actions" related to physical effects that require the introduction of traveling electromagnetic disturbances, that is quite sensible.

But this doesn't mean that every conceivable physical effect — considered under the framework of GR — absolutely requires a mediating signal, right?

An obvious example is the application of the mathematics of GR to the physics of gravitation. It should be safe to admit that not every gravitational model developed under GR is

**strictly required**to include the concept of propagating ("EM-like") signals, right?I think the technical way of asking this is: Does GR

**strictly require**that every curvature tensor that constitutes a gravitational field be "caused" by the influence of a spatially distinct stress-energy tensor? And if the tensors aren't spatially distinct, what sense is there in the idea that the values in the curvature tensors are actually "caused"?