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|WikiProject Physics / Relativity||(Rated Start-class, Low-importance)|
"Thus far, the results have failed to find any evidence of the Nordtvedt effect, demonstrating that if it exists, the effect is exceedingly weak."
- Can we quantify that? How weak must it be (or if you prefer, how strong can it be) before conflicting with experiment? RJFJR 19:06, 21 April 2007 (UTC)
- It can be quantified, but it's a bit messy. Directly, the difference in acceleration between the Earth and the Moon in the Sun's gravity is no more than about 1 part in 10^13. But the whole idea is that the difference is due to the gravitational self-energy, which is a tiny fraction of the Earth's total mass - about 1 part in 10^9. So when you divide out to get the "Nordtvedt parameter" (η) you get a limit - gravitational self-energy falls differently from other mass by at most (about) one part in 10^3. There have been some tests with pulsars (one is in progress right now), where the self-energy is 10-15% of their mass, but things get more complicated when you're in this strong-field regime. Exact numbers and discussion are available in section 4.3.1 of this review. Anne (talk) 00:36, 5 January 2018 (UTC)