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brotherbobby

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(2) Moreover, as someone mentioned in this thread, what happens to the speed of light? In Einstein's 1912 papers (a and b), he abandoned lorentz invariance and made time spatially dependent, ##c(x, y, z)##. So the speed of light is no longer an invariant in (the later) general relativity for coordinate systems. But worse, if space and time have lost their metrical meanings, assuming (1) above is true, how can an observer even measure the speed of light? Locally? Does space and time continue to have their meanings locally secure?

(3) Philosophically, focus has now shifted to matter and fields - see Einstein's fifth appendix in his famous expository book on the subject : Relativity - the special and the general theory. I did not understand it and am even baffled by it. I understand that space and time have been linked to matter, energy, pressure and even electromagnetic energy and momentum (via the two-index tensor). Does it mean however that space and time are mere illusions of something more physically fundamental (like the examples above)? But surely we can see space and time. How about an empty universe, with no matter and energy? Is general relativity saying that if matter and energy would be absent, so would space and time, implying there would also not be a universe at all?