Affine theories of gravitation ignore the EP, instead modeling gravitation as spacetime torsion. The two entirely different approaches give wholly identical predictions, with one class of exceptions: affine theories predict at least three classes of Equivalence Principle violation based upon test mass physical spin[1], test mass polarized electron spin[2], or test mass atomic lattice opposite geometric parity[3]. The first two are theoretically too small to observe.
Testing for reproducible Equivalence Principle violation is therefore of major interest. No violation beyond experimental error was ever observed. Test mass opposite parity EP experiments have never been performed. The proper test of spacetime geometry may be test mass geometry. Somebody should look.
Historic Equivalence Principle Tests[6]
| Year | Investigator | Accuracy* | Method |
|---|---|---|---|
| 500? | Philoponus[7] | "small" | Drop Tower |
| 1590? | Galileo[4] | 2·10-2 | Pendulum, Drop Tower |
| 1686 | Newton[5] | 10-3 | Pendulum |
| 1832 | Bessel[8] | 2·10-5 | Pendulum |
| 1910 | Southerns[9] | 5·10-6 | Pendulum |
| 1918 | Zeeman[10] | 3·10-8 | Torsion Balance |
| 1922 | Eötvös[11] | 5·10-9 | Torsion Balance |
| 1923 | Potter[12] | 3·10-6 | Pendulum |
| 1935 | Renner[13] | 2·10-9 | Torsion Balance |
| 1964 | Dicke,Roll,Krotkov[14] | 3·10-11 | Torsion Balance |
| 1972 | Braginsky,Panov[15] | 10-12 | Torsion Balance |
| 1976 | Shapiro, et al.[16] | 10-12 | Lunar Laser Ranging |
| 1981 | Keiser,Faller[17] | 4·10-11 | Fluid Support |
| 1987 | Niebauer, et al.[18] | 10-10 | Drop Tower |
| 1989 | Heckel, et al.[19] | 10-11 | Torsion Balance |
| 1990 | Adelberger, et al.[20] | 10-12 | Torsion Balance |
| 1999 | Baeßler, et al.[21] | 5·10-13 | Torsion Balance |
| 2005? | MiniSTEP[22] | 10-17 | Earth Orbit |
[1] Phys. Rev. D 66 022002 (2002)
[2] Phys. Rev. D 42 977 (1990)
" class="external">http://arXiv.org/abs/gr-qc/0102020
[3] " class="external">http://www.mazepath.com/uncleal/qz.pdf
[4] Galilei, Galileo. Discorsi e Dimostrazioni Matematiche Intorno a Due Nuove Scienze (Appresso gli Elsevirii, Leida: 1638) (Discourses and Mathematical Demonstrations Concerning Two New Sciences, Elsevier Press, Leiden: Netherlands, 1638)
[5] Jahrbuch der Radioaktivität Elect. 4 411 (1907)
[6]Ciufolini & Wheeler Gravitation and Inertia (Princeton University Press: Princeton, 1995) pp. 117-119
" class="external">http://einstein.stanford.edu/STEP/information/data/gravityhist2.html
[7]Philoponus, J, Corollaries on Place and Void David Furley trans.
(Ithaca, NY: Cornell University Press, 1987)
[8]Ann. Physik und Chemie (Poggendorff) 25 401 (1832)
[9]Proc. Roy. Soc. Lond. 84 325 (1910)
[10]Proc. K. Akad. Amsterdam 20(4) 542 (1918)
[11]Math. Naturw. Ber. aus. Ungarn 8 65 (1889)
Ann. Physik (Leipzig) 68 11 (1922)
Phys. Rev. D 61(2) 022001 (1999)
[12]Proc. Roy. Soc. Lond. 104 588 (1923)
[13]és Természettudományi Értesitö 53 569 (1935)
[14]Ann. Phys. (NY) 26 442 (1964)
[15]Zh. Eksp. Teor. Fiz. 61 873 (1971)
Sov. Phys. JETP 34(3) 463 (1972)
[16]Phys. Rev. Lett. 36 555 (1976)
[17]Bull. Am. Phys. Soc. 24 579 (1979)
[18]Phys. Rev. Lett. 59 609 (1987)
[19]Phys. Rev. Lett. 62 609 (1989)
[20]Phys. Rev. D 42 3267 (1990)
[21]Class. Quantum. Grav. 18(13) 2393 (2001)
Phys.Rev. Lett 83(18) 3585 (1999)
[22]" class="external">http://einstein.stanford.edu/STEP/