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Physics

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  • $\begingroup$ for that reason a metric (to use your word, map projection) is used to describe the space, and not differential geometry. This doesn't make sense. A metric is a tool used in differential geometry. $\endgroup$
    – user4552
    Commented Feb 8, 2018 at 0:53
  • $\begingroup$ A black hole on the other hand has mass, which means size Not true. An electron has mass, but as far as we know it's pointlike. $\endgroup$
    – user4552
    Commented Feb 8, 2018 at 0:54
  • $\begingroup$ @BenCrowell One should keep clear in mind that GR is a classical theory, and that elementary particles are quantum mechanical entitities. One cannot use quantum mechanical particles to argue GR points until gravity is really quantized ( unless you want to enter the mathematical terminology of strings where gravity is quantized but not yet modeling measurements, and most people would not be able to follow) . In classical physics there are no particles with zero mass and as far as I can see this answer is within classical physics. $\endgroup$
    – anna v
    Commented Feb 8, 2018 at 4:30