Mikko wrote:The isotropy of isotropic coordinates is not illusory.
It is in ISM case as earlier demonstrated. One has no reliable sense of how it relates to proper values, except in the trivial limit of zero gravity. Whereas SM anisotropy does at least permit an intuitive and accurate translation to the local space in Schwarzschild spacetime. And better again is genuinely isotropic Yilmaz metric.
It is a property of a coordinate system, not of space.
See above.
But the space has an important property, too: some spaces allow isotropic coordinate systems, some don't. That way having an isotropic coordinate system tells something about the space, whereas having an anisotropic coordinate system does not tell the opposite.
Exotic spacetimes not allowing (globally valid) isotropic coordinate systems are of no interest here - spherically symmetric matter distribution is the subject at hand.
The prose after the equation 1-7 needs correction. As written v3, it refers to spatial anisotropy as if it were a property of the space.
I may emphasize more often the distinction in v4, but it was already made clear numbers of times in v3 so seems to me you are just nitpicking or reading wrongly.
I cannot really comment the corrected text that I havn't seen, and there is no point to comment the erroneous text now that you understand at least the most obvious error.
Again you are imo nitpicking as I explained the context of it all in my last post. However given my thoughts below you get more than just a tidied up version of what you have now in v3. None of the present findings of self-contradictory nature of SM will change though.
The weak field calculations in section 2 are easier with isotropic coordinates. In a weak field the difference between the two coordinate systems is neglible.
Indeed but the easier use of ISM is at the cost of being intrinsically misleading aka useless - as already explained before. Might as well try portrait painting while wearing deliberately lens-distorted glasses. Simply adding (generally components of) radial and transverse components in ISM is not valid. They will have different true 'weights' in general, and to get those weights right is problematic and turns a deceptively 'simple' situation into a complex one. Ergo - stick to honest SM, to the extent one wants to know what Schwarzschild spacetime truly (multiply!) predicts.
The calculation is still easier in Cartesian coordinates. The spherical coordinates do not work that well for off-center masses. With isotropic coordinates the transition to Cartesian coordinates is simple.
I effectively worked in Cartesian coordinates in evaluation of part 2, and IF I proceed to generalize to off-center case, would stick with that approach.
The comparison to Yilmaz gravity is also easier in isotropic coordinates as the expression of the line element is much simpler than in Schwarzschild coordinates. Just make sure that you have the thin shell at the right place, which is defined in terms of the Schwarzschild coordinates. The isotropic radial coordinate is different, and in Yilmaz space different from Schwarzschild space.
If the analysis of the situation in Yilmaz space were properly written, it would be the most interesting part of the paper.
Already done for particular shell center case, in so many words in part 3 of v3. Given the genuine isotropy then applying, evaluation at center is trivial. Simple scalar addition applies - for both temporal and spatial components. The result is obvious without needing to perform integral calculus - interior with equal levels of 'redshift' for clocks and rulers, and with a smooth and natural boundary match to the external values. Something not possible with SM - as proven. Caveat follows!
For quite awhile have been slightly uneasy about two assumptions that are generally made and I have followed. That hollow interior is truly an equipotential region - probably only analytically proven for Newtonian gravity. And that exterior field truly is given by assuming an equivalent central point mass equal to the summed shell mass. Might pay to check both using part 2 method, for both SM and Yilmaz metric. That means an analysis for general r location. Won't be done anytime soon.
Another erratum note: Reference to zero Weyl curvature in my last post should have read 'spatial component of....', and best left to just saying Cotton tensor curvature everywhere zero.