Talk:General relativity

Wikipedia is written for narrow experts?

Wikipedia is written for narrow experts? What is the point of placing the forms of writing incomprehensible not to a narrow specialist? For example

$R_{\mu \nu }-{\textstyle 1 \over 2}R\,g_{\mu \nu }+\Lambda \ g_{\mu \nu }={\frac {8\pi G}{c^{4}}}\,T_{\mu \nu }$

is non-understandable form of writing. Why is the non-understandable form of writing is used unless an understandable form of writing for tensors? But the understandable form of writing is something like this:

$\mathop {\mu ,\nu } \limits _{\geq 0}^{n\leq }\left\{{R_{\mu \nu }-{\textstyle 1 \over 2}R\,g_{\mu \nu }+\Lambda \ g_{\mu \nu }={\frac {8\pi G}{c^{4}}}\,T_{\mu \nu }}\right.$

or

$\mathop {\mu } \limits _{\geq 0}^{n\leq }\left\{{\mathop {\nu } \limits _{\geq 0}^{n\leq }\left\{R_{\mu \nu }-{\textstyle 1 \over 2}R\,g_{\mu \nu }+\Lambda \ g_{\mu \nu }={\frac {8\pi G}{c^{4}}}\,T_{\mu \nu }\right.}\right.$

or

$\mathop {\left\{{}\right.} \limits _{\mu =0}^{n}\mathop {\left\{{}\right.} \limits _{\nu =0}^{n}R_{\mu \nu }-{\textstyle 1 \over 2}R\,g_{\mu \nu }+\Lambda \ g_{\mu \nu }={\frac {8\pi G}{c^{4}}}\,T_{\mu \nu }$

These forms of writing clearly indicate the system of equations and quantity of this equations. At the same time, this form is the same short. Unfortunately, it is difficult to find literature that would prove the importance of using such forms for better understanding by readers. At the same time, I do not understand why this problem is not obvious for writers. Voproshatel (talk) 08:18, 28 February 2023 (UTC)

Poincare

Lorentz thought that gravity was electromagnetic, but not Poincare. Poincare did have a relativistic gravity theory. See . So I do not think the last edit is correct. Roger (talk) 05:15, 24 July 2023 (UTC)

Weinstein translates a crucial passage from his 1905 note (which he expanded to a full paper in 1906) as follows: "If we were to admit the postulate of relativity, we would find the same number in the law of gravitation and the laws of electromagnetism – the speed of light – and we would find it again in all other forces of any origin whatsoever. This state of affairs may be explained in one of two ways: either everything in the universe would be of electromagnetic origin, or this aspect – shared, as it were, by all physical phenomena – would be a mere epiphenomenon, something due to our methods of measurement".

In other words, Poincare expressed a faith that either (1) gravitation would ultimately prove to be of electromagnetic origin, or (2) both gravitation and electromagnetism would be "epiphenomena" of some deeper theory.

In both 1905 note and his 1906 article, Poincare argued against an infinite speed of gravitation as representing a violation of the principle of relativity, which he considered absolute. Asserting that gravitational forces must obey the principle of relativity is, in my opinion, a far cry from being able to state that Poincare had anything resembling a relativistic theory of gravity. However, it would be correct to state that Poincare derived some results in what would today be called "relativistic gravitation". Prokaryotic Caspase Homolog (talk) 08:20, 24 July 2023 (UTC)

I guess you are agreeing that it is incorrect to say option (1) is Poincare's belief. He is favoring option (2). Option (2) does not say that gravitation and electromagnetism are from a deeper theory. It says that "this aspect" (propagating at the speed of light) is "due to our methods of measurement". That option is not much different from what many say today.

Weinstein says "when discussing his theory of gravitation, Poincaré extended his mathematical theory of groups from electrodynamics to gravitation." Damour says "Poincare’s June 5, 1905 Note announces important mathematical and physical advances in what we would call today, Special Relativity, relativistic electrodynamics and relativistic gravitation". Walter says "In July, 1905, Henri Poincaré (1854–1912) proposed two laws of gravitational attraction compatible with the principle of relativity and all astronomical observations explained by Newton’s law." So I think it is fair to say Poincare proposed a relativistic theory of gravity. Roger (talk) 17:22, 24 July 2023 (UTC)

I would no more state that than I would agree that Einstein proposed a relativistic theory of gravity in 1907 because, using relativistic arguments, he predicted gravitational time dilation and, in 1911, the bending of light. Einstein made a few predictions, but he had not yet tied everything together in a coherent theory. Neither did Poincare. Prokaryotic Caspase Homolog (talk) 20:54, 24 July 2023 (UTC)

Your edit is still wrong. You say Poincare made an "assumption that gravitation should ultimately have a common origin with electromagnetism". That is not true. Poincare said that Lorentz made such an assumption, and Poincare was pointedly not making that assumption. Then you say that he made a prediction as a consequence of that assumption. None of the primary or secondary sources say that. On the contrary, Poincare said that it was a consequence of his relativity theory that nothing goes faster than the speed of light. Before Poincare, it was thought that gravity went faster. Roger (talk) 01:59, 25 July 2023 (UTC)

References

Problems with Einstein's general theory of relativity

The article " Problems with Einstein's general theory of relativity " was online for about eight or so weeks but then failed to survive a vfd.

If anyone's looking for the content, it's now online again, at http://dx.doi.org/10.13140/RG.2.2.16665.12649

This seems to be the best listing of its type available. The problems highlighted are specific to the consequences of Einstein's 1913-1916 attempt to construct a general theory, starting from an SR foundation (an approach that he later rejected, in 1950) ... that is, they are not obviously issues with the fundamental concept of a general theory, only with Einstein's flawed attempted implementation. You're welcome. ErkDemon (talk) 20:43, 18 January 2025 (UTC)

Current Research Section (Instability of Black Holes)

I think this would be a good section to add to this article. I believe that this would be beneficial especially for people that are interested in seeing how this theory of gravity is applied to research currently, so with this I wanted to gauge how much interest there would be for this? With that, I want to expand in particular the horizon instability of black holes history. Anyways, if you could provide your feedback on this I would greatly appreciate it! Thank you so much in advance for taking the time to read this! Jace Green (talk) 17:24, 9 April 2026 (UTC)

Might be too advanced for this article. Constant314 (talk) 01:53, 10 April 2026 (UTC)

Thank you for the feedback! Do you know of any articles could benefit from this? Like I was thinking of adding this on the black hole article possibly? Jace Green (talk) 01:00, 11 April 2026 (UTC)

Is there an error in the field equations?

Under "Einstein's equations" there's a green box with "Einstein's field equations". The equation seems to be missing the "+\(\Lambda \)\(g_{\mu \nu }\))" term. It's present on https://en.wikipedia.org/wiki/Einstein_field_equations, but not in this page. T Hawk 42 (talk) 19:25, 8 September 2026 (UTC)

As it says in that other article, "The effect of the cosmological constant is negligible at the scale of a galaxy or smaller.". So it is unnecessary to use it when considering the movement of celestial bodies within the solar system, a globular cluster, or even the whole Milkyway galaxy. It amounts to a very very tiny repulsive force proportional to the volume of a ball centered on one object having a radius equal to the distance to the other object. The error caused by ignoring it is millions of times less than the error caused by using Newton's law instead of Einstein's. JRSpriggs (talk) 22:34, 8 September 2026 (UTC)

But only at a galatic scale -- the article doesn't say that. It doesn't mention (Lambda )(g_{mu nu })) at all, not even to say that's it's "negligible so ignored here". And it is a part of the equations.

This had me very confused for quite some time trying to work out why one page was saying one thing, and another page was saying another. Other sources mention that missing term all the time.

And in an article about General Relativity it seems important, to me at least, that it should be there and not summarily discounted in the entire page. #confused T Hawk 42 (talk) 12:38, 9 September 2026 (UTC)