Una teoria del campo gravitazionale generato da un mezzo materiale continuo, può essere anche formulata a partire dallo spazio-tempo pseudo-euclideo nonrinormalizzato, come una teoria di campo nella quale il potenziale gravitazionale è rappresentato da un tensore doppio simmetrico $\psi_{\alpha\beta}$ Avendo adottato, per comodità, una formulazione variazionale, la natura continua della materia gravitante introduce vincoli nuovi rispetto al noto caso della particella puntiforme. La teoria viene costruita in modo iterativo; nella pre sente Nota vengono dati gli sviluppi dettagliati, di possibile utilità applicativa, sino al secondo ordine.
Referenze Bibliografiche
[1] See for example J.A. WHEELER, in The Physicist's Conception of Nature, Dirac 70th anniversary volume (Dordrecht and Boston).
[2]
W. THIRRING (
1961) - «
Ann. Phys. (N.Y.)»,
16, 96. See also
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MR 135564[3]
S. DESER (
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MR 391862[5] G. CAVALIERI and G. SPINELLI (1977) - «Nuovo Cimento», 39 B, 93.
[6] C. CATTANEO (1973) - «Boll. U.M.I.», 8 Suppl, fasc. 2, 49.
[7] We employ here point transformations, not to be confused with coordinate transformations. See for instance, F. PLYBON (1971) - «Journ. Math. Phys.», 12, 57.
[8] G. CAVALIERI and G. SPINELLI (1977) - «Nuovo Cimento», 39 B, 87.
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L. D. LANDAU and
E. M. LIFSHITZ (
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The Classical Theory of Fields, second edition (Oxford,
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MR 143451 |
Zbl 0178.28704[11] Directly by the definition of the deformation tensor. See for example
L. D. LANDAU and
E. M. LIFSHITZ (
1959) -
Theory of Elasticity, (London) Chapt. 1. |
MR 106584[12] Parentheses containing two indices, denote symmetrization, e.g. $\psi_{\alpha(\beta;\gamma)} = \psi_{\alpha\beta;\gamma} + \psi_{\alpha\gamma;\beta)}$. The traces of tensor are written by suppresing the repeated indices e.g. $\psi_{\sigma}^{\sigma} = \psi$. Finally $\square$ is the d'Alembertian operator i.e. $\square \psi_{\alpha\beta} = \psi_{\alpha\beta;\lambda^{\lambda}}$.
[13] W. WISS (1965) - «Helv. Phys. Acta», 38, 469.
[14]
R. H. DICKE (
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The Theoretical Significance of Experimental Relativity, (New York, N.Y.). |
MR 189749 |
Zbl 0148.46006[15] As shown in Ref. [2] an atom put in the gravitational field, undergoes, in the linear approximation, a deformation given by a tensor $f\psi_{\alpha\beta}$. It is the same deformation to which real rods and clocks (made out of atoms) are subjected, so that a real observer does not measure a pseudo-Euclidean but a Riemannian space-time. Taking into account that the matter is made out of atoms, all the objects are deformed by gravity in the unrenormalized picture. Hence, in such space-time a variation $\delta\psi_{\alpha\beta}$ causes an increase of the deformation tensor equal to $f\delta\psi_{\alpha\beta}$.