Black hole at the beginning of time

[PeroK]

Is impossible as you state it here since, as @vanhees71 has correctly pointed out, isotropy about only one point does not imply homogeneity.

It's clear from the context that "isotropic" means isotropic at every point. That must be the default terminology in any case.

 

[vanhees71]

Well, it's obvious that isotropy around only one point is not enough. It's however also pretty intuitive that isotropy around all points implies homogeneity (but not the other way, i.e., homogeneity does not imply isotropy around any point). Weinberg's definitions and proofs in Gravitation and Cosmology (Chpt. 13) is also not too difficult to follow.

 

[cianfa72]

No global chart in any curved spacetime can be inertial.

Yes that's is true in general, in the particular case of chart described in #56 the reason behind it should be that pointed out there, I believe.