Quote:
Originally Posted by sjastro
You have two frames of reference. In the Universe frame of reference, objects (not gravitationally bound) are at fixed points while space-time undergoes metric expansion.
Then there is the observers frame of reference. A distant galaxy moving under metric expansion will appear to move way from the observer.
An observer will be able to measure time dilation of a supernova light curve, which like the recession velocity of a distant galaxy is a function of cosmological redshift. This the key point to metric expansion.
For objects moving away in space which are not too distant, time dilation is a function of the velocity of the object and independent of cosmological redshift.
Regards
Steven
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If I've got that right, that means there's sort of a dual reality being formed, where all points (all reference frames) within the universe retain laws (doppler effects), and a global reference frame which does not retain the laws (so cannot exist as part of physical spacetime)...this would mean that a Metric Tensor or Metric Inflation, does not have any real [physical] property at all, it can only be a mathematical expression of what's occurring...which would then indicate to me that a gravity wave is also just a dynamic mathematical change within the metric at any given point in spacetime. If that's the case, then a Metric can only effect spacetime, as it is not a physical part of spacetime.
I wonder if this was the type of issue which indicated to Einstein that he needed to abolish his universal frame of reference (fixed background structure) after using it to put together SR. From then-on he always worked with "no fixed background structure" in his TOE work.