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i read an article by S.carlip about quantum gravity, arXiv:gr-qc/0108040v1 ,

in this article carlip stated:

why we need quantum gravity

what's problems of quantum gravity

and two ways of quantization of GR.

I couldn't realize some clues in section of "the problems of quantum gravity"

one of them is

General covariance vs. locality that Carlip stated:

The fundamental symmetry of general relativity is general covariance (strictly speaking, diffeomorphism invariance), the lack of dependence of physical quantities on the choice of coordinates. Observables in quantum gravity should presumably respect this symmetry . But diffeomorphism-invariant observables in general relativity are necessarily nonlocal , essentially because active coordinate transformations “move points” and cannot preserve a quantity deﬁned, by its value at individual points.

I can't understand this phrase

is it possible to explain it for me.

thanks

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# General covariance vs. locality

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