Dear Eckard,
If, as I propose, light propagates in the gravitational field (gravity as ether) then there is no way to avoid gravitomagnetics in attempting to understand energy-time physics vs space-time symmetry. I suggest that you may wish to review the Hafele-Keating and Michelson-Gale-Pearson experiments (pages 45-52 in 'Everything's relative...') to grasp the necessity of gravity for interpreting these experiments.
I was made aware of a paper by Al Kelly, circa 1995, that came to the same conclusions (based on these and other experiments) that I have reached. I have a copy of the pdf, but no link to it.
In short, gravity defines a local absolute, which finally answers the problems of energy associated with the concept of "energy of relative motion".
I do not know how many times you have read 'Everything's relative...', but there is far too much information for anyone to absorb in only 2 or 3 readings, and impossible to transfer to FQXi comments in any meaningful fashion.
Best regards,
Edwin Eugene Klingman