作者: Hans-Jurgen Schmidt
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摘要: The following four statements for indefinitemetrics of Lorentz signature do not possess an analogousstatement in the definite Euclidean case: (1)All curvature invariants a gravitational wave vanish, spite fact that itrepresents nonflat spacetime. (2) eigennullframecomponents tensor (the Cartan“scalars”) represent curvaturescalars. (3) topology Minkowskispacetime doesnot possessa basis composedofLorentzinvariant neighborhoods. (4) There are pointsin de Sitter spacetime which cannot be joined toeach other by any geodesic. We show these fourstatements all follow from noncompactness theLorentz group. conclude popular (and oftenuseful) imaginary-coordinate rotation to Lorentzian (called Wick rotation) isnot isomorphism.