From: tjroberts137@sbcglobal.net
On 3/27/17 3/27/17 2:08 AM, Stefan Ram wrote:
> Tom Roberts writes:
>> Also see my earlier post in this thread -- in the solar system the
>> approximation holds, and even though gravity "propagates" with speed
>> c, the "gravitational force" essentially extrapolates objects'
>> positions to "now" so it is essentially as if gravity "propagated
>> instantaneously".
>
> It would be too strange if this would open any door to
> transfer information instantaneously (faster than light).
Just like the Lienard-Wiechert potentials of classical electrodynamics, this
obeys the maximum speed of c. It is the extrapolation that makes it LOOK as if
gravity "propagated instantaneously" -- but gravity does not actually do so in
GR.
> So something must be in power to avoid this.
Yes. The local Lorentz invariance of the equations. Such symmetries are the
foundations of physics.
> It could be
> that "nothing surprising" can happen in the world with
> regard to the gravity field in the sense that the extrapolation
> you mention must coincide with the real behavior.
Hmmm. The predictions of both CE and GR agree very well with the results of
experiments. So they do "coincide with the real behavior", at least within
their
domains.
> If one could "surprisingly" create a large amount of energy
> at a place, we would not expect this new information to
> be able to escape faster than light. This might indicate
> that such an event (a "surprising" creation of energy at a
> place) is not possible.
The local conservation of energy also prohibits that. GR has nothing to say
about such an unphysical scenario. That is, it is not possible to construct a
manifold in which that happens and which also satisfies the field equation. But
also, nobody has ever reported observing such a scenario in the world we
inhabit.
Tom Roberts
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