[Nesti (Mark)]

Geez, this conversation is so confusing.

From my understanding, there is no such thing as the speed of gravity. Einstein showed (and someone correct if I'm wrong here), that it is the field of acceleration (Gravitational Field) which propagates outward at c...it does this because it is the changes of the metric values which travel outward at c, nothing else, but these changes affect the expression of the field of acceleration left in its wake. The field is constantly maintained in the same manner, but remove the origin (energy/mass) and the metrics changes [to flat spacetime] and these changing values then propagates outward at c also. The expression of the field at any part is attributed to both the field origin - which dissipates at the rate of 'one over 'r' squared - as well as any local mass (energy/momentum) within the original field. The local energy and matter creates its own field of acceleration (local gravity) but merges in with the overall field too (it too dissipating and the rate of 'one over 'r' squared), so we can have local gravity fields within the larger field...ergo the concept of a 'Test Particle' is that it is infinitely small with infinitely small mass so it is able to 'survey' the metric at any given position but without affecting the field...of course it is hypothetical and just for the math.

The constancy of light - in vacuum or otherwise - becomes unworkable since spacetime becomes sympathetic to light's constancy. We have NO background template or benchmark with which we may make comparison, and since the gravitation field itself is forever in dynamical change, how can we ever hope to make any successful measurement. If the photon carried information about the global system, then perhaps there would be a way forward.

One of Einstein's most important descriptions of spacetime went something like "dimensions are not a vessel in which space-time is contained, yet events are spatially [and temporally] separated"...if we have just one photon in an empty field, then there is no field! Any measurement conducted WILL also affect local spacetime, thus any data and conclusions as you yourself impart a field influence. Also, who's frame of reference will you be using, as ALL frames are valid?

Einstein deduced the speed at which the metric is influenced (and gravity wave propagation) is equal to the speed of light simple because the math showed that it does. I personally attribute this to the properties of spacetime itself and not the light (photon): The stress energy.

Anyway, for me the question of the speed of gravity makes no sense...whereas light constancy and simultaneity means everything!

If you want something that operates faster than light, a non-influence perhaps, I feel that the regulation of the force [mediating] particles and particle physical values (mass, charge, isospin etc) are instantaneous. Yes, I know this breaches a central condition of SR...but I also believe particle information doesn't necessarily have to 'move' in order to propagate throughout the universe (On this one Steven, I'm talking regulatory function of particle values only and regulation/fixing of the number of force particles, and not the passage of any information or influence, in this way causality might not be violated).