Talk:Tests of general relativity

General Precession

The stated value for the general precession in longitude, 5025.6 arcsecond/julian century IS incorrect.

Newcomb's value for the general precession was p = 5025.64 arcseconds per tropical century at the Besselian epoch B1900.0

The modern epoch is J2000.0. Since the length of the tropical century isn't constant, astronomers now use the Julian century. The error in confounding the two is about .1 arcsecond per century.

More recent adopted values for the general precession are:

5029.0906 IAU (1976)

5028.7922 IAU (2003) [1]]

5028.7955 (±.0003) Fukushima (2003) [2]]

5028.8300 (±.04) NASA (current) [3]]

The table listing the sources of precession implies an impossible level of accuracy. The accuracy is limited by pertubation of the 300,000+ unmodeled asteroids, the imprecisely known values for Mercury's prolateness (C22 equatorial eccentricity), and the large offset between Mercury's center of mass and it's center of figure (J1). It's either a stunning cooincidence, or the uncited numbers were simply pulled out of someone's behind.

As noted in the article, the confirmation bias for General Relativity is astronomical. Impossibly accurate agreement between theory and observation are often justifiably interpreted as evidence that the theory is incorrect. In this case, any knowlegeable person could easily recognize the information in the table cannot be trusted. First off, there is no citation. Secondly, there is no citation. Thirdly, there is no citation. Fourthly, due to a secular increase in the general precession, the associated epoch must also be given. Fifthly, "century" is ambiguous, it could be julian, besselian, or tropical. Sixthly, the most accurate determination of the observed perihelion precession is NOT made by radar, it is made by analyzing numerical ephemerides such as DE405.

Finally, the author actually proves his bias and his willingness to misrepresent experimental results:

"Einstein showed that general relativity predicts exactly the observed amount of perihelion shift".

Exact agreement! I'm convinced.

Today we measure locations in space relative to the inertial ICRF. The historical observations should be put in this context by taking out their observed frame effects. This makes the observation of the Equinoxes irrelevant to the calculation (as Earths orbital parameters should be, after they are used to calculate the effect of their tug on Mercury.) Using Clements, this gives an observed precession of:

5599.74±0.41 - 5025.64±0.50 = 574.10±0.65 — Preceding unsigned comment added by Utesfan100 (talk • contribs) 17:10, 24 November 2011 (UTC)

I agree, in Einstein's time the empirical values of e.g. Mercury's precession rate would not have been known to very high accuracy, much less “infinite” accuracy. Still, the observation and theory (general relativity) matched pretty nearly, which would've looked good. Btw, center of figure is also called a centroid.--Solomonfromfinland (talk) 16:21, 27 June 2016 (UTC)

Will the Square Kilometre Array be used for "Extreme tests of general relativity"

The claim is made that the Square Kilometre Array be used for "Extreme tests of general relativity" in in this WP article:

https://en.wikipedia.org/wiki/Square_Kilometre_Array#Extreme_tests_of_general_relativity

Is that true?

If so, might our general relativity testing article explain what tests of general relativity are anticipated to be done with the Square Kilometre Array, how those tests differ from tests already done or planned, what about the SKA tests will be "extreme," what results are predicted, and how receipt of results confirming or (especially) differing from the expected might trigger a re-thinking of general relativity theory, and how. Any practical implications would be especially interesting to include. -- Ocdnctx (talk · contribs) 00:43, 17 July 2014‎

Inferring from "By using pulsars as cosmic gravitational wave detectors, or timing pulsars found orbiting black holes," at the article and section you linked:

Since pulsars are extremely regular in their timing, one could watch them carefully for isolated phase shifts which would indicate that a gravitational wave had passed between the pulsar and us.

Or one could compare the periodic phase shifts caused by orbiting a black hole with what theory (GTR) predicts.

Beyond that I would not want to speculate. We would need to find reliable secondary sources describing such tests before including them in this article. That is unlikely to happen until after the necessary primary research has been done, if indeed it can be done (we need to find pulsars in the proper situations to do this). JRSpriggs (talk) 04:41, 17 July 2014 (UTC)

The SKA can certainly be used as a pulsar timing array. Whether or not it actually sees gravitational waves depends upon the astrophysics of the sources. Whether or not this counts as an extreme test is debatable. (1) Other radio telescopes could measure the same thing. (2) Other types of gravitational-wave detector could perhaps place better constraints sooner, e.g. LIGO. (3) Detecting a gravitational-wave background from massive black-hole mergers (the most likely source) might not be a sensitive test of GR.

Observing a pulsar orbiting close to a massive black hole would count as an extreme test (possibly akin to gravitational-wave measurements of extreme mass ratio inspirals). I am not sure how probably such a configuration is. I don't know if anyone knows how probable that is.

A possible reference is this Living Review.— BobQQ (talk) 08:17, 18 July 2014 (UTC)

GR tests

Paragraph 2: Black holes do not depend on GR strong gravity. Laplace knew it, based on Newtonian gravity. GR just makes a difference of a factor 2 in the size. We should care about history and also simple truth. Who wrote this with no citations? Jmalick9 (talk) 02:14, 8 August 2015 (UTC) --Jmalick9 (talk) 02:14, 8 August 2015 (UTC)

FP

I'll rephrase my post: apparently tests of relativity are largely reliant/dependent on free parameters. In the interest of full disclosure, I would like this to be addressed in layman's terms. Subuey (talk) 17:58, 30 March 2017 (UTC)

See Test theories of special relativity for an example. To test a theory one needs either one-or-more alternatives to compare it with or a more general theory (having more free parameters). Otherwise the results of experiments have nothing to work against. See Bayes' theorem. JRSpriggs (talk) 02:55, 31 March 2017 (UTC)

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Deflection of light from galaxies by a star

"such a ring formed by the deflection of light from distant galaxies has been observed for a nearby star.[28]"

The source quoted only refers to the deflection of the light from a background star by another star, there is no mention of distant galaxies or from a ring.

Rings from distant galaxies have been observed, but around nearby galaxies (not stars) so there seems to be a mixture of the two results and an inappropriate reference. — Preceding unsigned comment added by 78.194.166.238 (talk) 06:35, 29 March 2019 (UTC)

Edit request: Is "Gravitoelectric effects (Schwarzschild-like)" a General Relativity effect?

The first table in the article does not explicitly state that the "Gravitoelectric effects (Schwarzschild-like)" is a General Relativity effect. I am not a physicist but I suspect the two terms mean the same thing, given the similar sizes of the effects (43 arcseconds in a preceding paragraph, and 42.98 arcseconds in the table). If my suspicion is correct, please reword the table so that the words "General Relativity" appear in it. Otherwise the table is unclear to the lay reader.86.136.201.152 (talk) 17:31, 25 August 2019 (UTC)

Anomalous Mercury Perihelion Precession Rate from Classical Mechanics

A new book, "Air of Doubt" (ISBN: 979-8697917329) by Dr. Frank A Tinker, offers an argument for modifying Kepler's Third Law in the same spirit as Newton's modification adding planet masses. The proposal is to add a factor involving the orbital energy to improve the comparison of two planet's orbits. In doing so, he resolves the Mercury perihelion precession anomaly without resorting to General Relativity. As such, he shows that the Theory of General Relativity is not necessary in order to resolve the anomaly. Which means General Relativity can't really use the solution to show superiority over classical mechanics.

For completeness, it appears that reference and proposal should be included in this topic. Link: www.airofdoubt.com.

Yes, that is me. But I'm not about to edit this without discussion. AoDFT (talk) 01:11, 20 October 2020 (UTC)

Revert of edit, June 10, 2021

I reverted this edit by Ruhenheim (talk | contribs) because the grammar was sloppy, the formatting was sloppy, and it used British English, while the article is in American English. If the material is important enough to be inserted, it will need to be cleaned up first.—Anita5192 (talk) 14:42, 17 June 2021 (UTC)

I have removed the unnecessary inclusions and only kept the first part which corrects the physics.

"Under Newtonian physics, a two-body system consisting of a lone object orbiting a spherical mass like a star would trace out an ellipse in the star's frame with the star fixed at a focus." Will this work?--Ruhenheim (talk) 18:12, 19 June 2021 (UTC)

I inserted your edit, replete with citation, after cleaning it up for grammar and formatting, and corrected some other subtle inaccuracies in the existing paragraph. I omitted some of the references to stars and planets to make the treatment more general.—Anita5192 (talk) 19:08, 19 June 2021 (UTC)

Thanks--Ruhenheim (talk) 17:50, 22 June 2021 (UTC)

Precession of the Perihelion of Mercury

I have made a minor change to help explain the direction of the precession. In the reference it says that that the precession is in the direction of the plane of the orbit. Not knowing anything about celestial mechanics I assumed it was 90 degrees to the plane of the orbit, and this was only corrected when I read the original citation. I think it would be much clearer to also include this in the wikipedia article. Eparaqutam (talk) 00:59, 4 November 2023 (UTC)