Quote:
Originally Posted by sjastro
Mark,
The absolute frame of reference you are alluding to doesn't exist.
There is no benchmark, no absolute measurement that can be used as a basis for comparison.
Each observer is making a valid measurement in their own frame of reference. No observer is more right or wrong than any other observer.
The speed of gravitational waves is an invariant quality like the speed of light or the electron charge, it has the same value for all observers.
Regards
Steven
|
That's exactly my point Steven and I do see what you are saying. But you're still making an observation of one frame of reference from yet another frame of reference and then labeling the entire universe to this or that. Furthermore, to achieve such evidence you will need some distant event that has both a light source to measure against and a substantial mass/energy event. Both metric value change and light wave MUST propagate through the same spacetime region to the measurement equipment to ENSURE that the spacetime topology is consistent for both. But, you will never know the topology of the spacetime if the light is riding the bow of the metric wave (so to speak). You will never have a valid argument as we still only ever observe an 'apparent' constancy of light, an 'apparent' change in metric values and an 'apparent' doppler shift in a gravity wave and in light. Any two apparents don't make a whole.
Also, don't be surprised if something funny happens, that light outruns the metric at c also...as that would kill any an all arguments about spacetime and confirm Einsteins two constants of the universe in SR.
For me there are two absolutes, the constancy of light speed and laws, everything else is malleable, and that must also include not only spacetime, but also the metrics ability to vary. So if light were impeded through space the rate at which the metric could propagate would vary also. Any change in the metric could never get ahead of light itself (as shown in Minkowski space and the null cone) This universe is built upon the properties of light and properties of energy, not space and/or time. Saying that changes in the metric can propagate faster than light would be like saying the metric ignores its own topology, ergo operates outside spacetime itself.
If someone asked me how fast does the metric values change in a gravitation field, I would have to say that the metric gets its instructions from light. If light took 50 years to move from the central core of our sun to its surface, then so would any changes in the metric.
At the end of the day, we're talking about a phantom...gravity waves, ie detectable changes in the metric have never been observed, they only ever leave their footprints (tidal effects), and many have given up on ever finding them. The notion that you can detect them using light is great if you're looking for a permanent research grant, so those people tend to look toward more promising horizons; dark matter (LOL). This is yet another classic example as to why String Theory offers so much promise, in that higher dimensional metrics can orchestrate all of these spacetime disjointed pieces in to an orderly pattern, an orderly reality.