# Talk:Alternatives to general relativity

WikiProject Physics / Relativity  (Rated Stub-class, Low-importance)
This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Stub  This article has been rated as Stub-Class on the project's quality scale.
Low  This article has been rated as Low-importance on the project's importance scale.

Welcome to a new Wikipedia page. I started it after finding that Wikipedia articles on gravity and alternatives to General Relativity were a complete mess, with several excellent articles (eg. on Brans-Dicke), many substandard entries, and nothing like a proper index.

As I write this the page is still under construction. I've still to add the rest of the equations, a big table of PPN results, add footnotes, add all the cross-references within, from and to the article, and fix the glaringly obvious faults.

So please don't edit the page until 2 Sept 2006. After that, go for it! Mollwollfumble 01:09, 25 August 2006 (UTC)

My advice is to keep plugging away on this article. In both content and title it is much better than classical theories of gravitation. --EMS | Talk 03:12, 31 August 2006 (UTC)

## Suggestions for improvement

Hi there. I would really like to see this article improve, as it has the potential to be a very good article indeed. That's not to say it's not a good artile at the moment. I would say that, overall, most (all ?) of the important information is already present in the article (good work Mollwollfumble!). The only question is one of making the article much better (by Wikipedia's rigorous standards). I would like to suggest the following improvements/points for discussion:

• The 'Classification of theories' (section 4.1) should come before the 'Early theories' section (number 3).
• Having thus classified the theories, is it better to group the theories in chronological order or by type (bimetric theories, scalar theories etc...) ? My preference is by type; this should be discussed though.
• The 'Testing of alternatives to GR' section could be split of into another article. Thoughts ?
• There should perhaps be main article links to the articles that describe the theories in more detail (as there is for the 'Testing of alternatives to GR' section) - this is mainly for better and more consistent presentation.

These are just a few ideas off the top of my head that I felt should be worth discussing to improve the article. Mollwollfumble, you have done some very good work in presenting details of Lagrangians etc... and finding all those references. I hope more editors will be encouraged to help improve this article. Thanks for reading this. MP (talk) 20:00, 1 April 2007 (UTC)

This appears under "Cosmological Tests": With GR, the combination of baryonic matter, dark matter and dark energy add up to make the universe exactly flat. " I'm not an expert, but last time I looked, a positive cosmological constant was confirmed with high confidence. —Preceding unsigned comment added by Fairandbalanced (talkcontribs) 04:57, 30 July 2008 (UTC)

## Process Physics

The section for Process Physics, under "Other Modern Theories", seems to have been removed for the reason that it has not been published in well-known notable journals. May I suggest you read Process Physics, including it's talk section, and reconsider whether it belongs here or not. There are several scientific articles referenced on that page which would definitely be worth a look.

I personally think it at least needs to be mentioned as an alternative theory, with a link to the main article. I'll leave it up to you as to what you want to do with this. Bill Killed The Unicorns

As far as I see, process physics is in the category "fringe physics" and the "Fringe subjects without critical scientific evaluation". Ok, I'm also interested in alternative theories, but what do you think is happening if every non-mainstream theory, which is not published in reputable sources, will be included in the article? For example, look at Heim theory and so on. --D.H 09:19, 4 May 2007 (UTC)

You make a good point, but since the article is "Alternatives to general relativity" it would be a bit biased to exclude some just becuase they don't have as much evidence behind them as some of the others mentioned here. Perhaps a better alternative would be to add a section entitled "other theories" or something like that, and then list there links to all other alternative theories, including those that have too little evidence behind them to merit a detailed explanation in this article. And then if one particular theory gets some better evidence to support it, it will be a reasonably simple process to add a new section to this article where it does get a detailed explanation. Bill Killed The Unicorns 02:50, 11 May 2007 (UTC)

## Transported text

I've transferred the following text from Talk:General relativity/WIP#Alternatives to general relativity; that section has been considerably shortened, but the removed info. (i.e. the following text) may still be useful for this article:

• Nordström's theory of gravitation (1913) was one of the earliest metric theories (an aspect brought out by Einstein and Fokker in 1914). Nordström soon abandoned his theory in favor of general relativity on theoretical grounds, but this theory, which is a scalar theory, and which features a notion of prior geometry, does not predict any light bending, so it is solidly incompatible with observation.
• Alfred North Whitehead formulated an alternative theory of gravity that was regarded as a viable contender for several decades, until Clifford Will noticed in 1971 that it predicts grossly incorrect behavior for the ocean tides.
• George David Birkhoff's (1943) yields the same predictions for the classical four solar system tests as general relativity, but unfortunately requires sound waves to travel at the speed of light. Thus, like Whitehead's theory, it was never a viable theory after all, despite making an initially good impression on many experts.
• Like Nordström's theory, the gravitation theory of Wei-Tou Ni (1971) features a notion of prior geometry, but Will soon showed that it is not fully compatible with observation and experiment.
• The Brans-Dicke theory and the Rosen bimetric theory are two alternatives to general relativity which have been around for a very long time and which have also withstood many tests. However, they are less elegant and more complicated than general relativity, in several senses.
• There have been many attempts to formulate consistent theories which combine gravity and electromagnetism. The first of these, Weyl's gauge theory of gravitation, was immediately shot down (on a postcard) by Einstein himself,[citation needed] who pointed out to Hermann Weyl that in his theory, hydrogen atoms would have variable size, which they do not. Another early attempt, the original Kaluza-Klein theory, at first seemed to unify general relativity with classical electromagnetism, but is no longer regarded as successful for that purpose. Both these theories have turned out to be historically important for other reasons: Weyl's idea of gauge invariance survived and in fact is omnipresent in modern physics, while Kaluza's idea of compact extra dimensions has been resurrected in the modern notion of a braneworld.
• The Fierz-Pauli spin-two theory was an optimistic attempt to quantize general relativity, but it turned out to be internally inconsistent. Pascual Jordan's work toward fixing these problems eventually motivated the Brans-Dicke theory, and also influenced Richard Feynman's unsuccessful attempts to quantize gravity.
• Einstein-Cartan theory includes torsion terms, so it is not a metric theory in the strict sense.
• Teleparallel gravity goes further and replaces connections with nonzero curvature (but vanishing torsion) by ones with nonzero torsion (but vanishing curvature).
• The Nonsymmetric Gravitational Theory (NGT) of John W. Moffat is a dark horse in the race.

MP (talkcontribs) 20:58, 29 November 2007 (UTC)

## How about just tweaking the dependence of the action on the Riemann–Christoffel tensor?

In Einstein–Hilbert action, we see that the Einstein field equations follow from using a constant times the Scalar curvature as the gravitational Lagrangian. Suppose we just add a little bit of the square of the Riemann–Christoffel tensor, ${\displaystyle R_{\beta \gamma \delta }^{\alpha }R_{\nu \rho \sigma }^{\mu }g_{\alpha \mu }g^{\beta \nu }g^{\gamma \rho }g^{\delta \sigma }\,}$? Have any alternative theories like this been proposed or evaluated? JRSpriggs (talk) 18:22, 13 June 2008 (UTC)

I should have said something about why one would want to do this. I was wondering how we could modify general relativity to eliminate the problem of singularities. If intense gravitational fields created anti-gravity (similar to the cosmological constant), then that might do it. Adding a term like the one I mentioned (if one gets the sign right) might do it, I hope. JRSpriggs (talk) 14:55, 15 June 2008 (UTC)
I recently saw a mention of Einstein-Gauss-Bonnet gravity which apparently adds a small contribution for the square of the Riemann-Christoffel tensor and the square of the Ricci curvature and the square of the scalar curvature. I think that this article should cover EGB! JRSpriggs (talk) 06:42, 20 July 2008 (UTC)
Throwmeaway (talk · contribs) just created an article on Gauss-Bonnet gravity. JRSpriggs (talk) 07:16, 4 July 2010 (UTC)

## New alternative gravity theory

There is a new gravity theory that has been published. It passes all experimental tests of GR, and in addition a corporation is using the new theory as the basis for their alternative energy tests. This theory should really be listed on this page... even if it is just a link to the theory. The theory is called Gravity Theory Based on Mass-Energy Equivalence. Gravityforce (talk) 22:54, 20 November 2008 (UTC)

## J. W. Moffat?

I can't find the article for J. W. Moffat. Anybody know what it is listed under?

Moffat is of no help. FX (talk) 20:02, 4 February 2009 (UTC)

Is John Moffat (physicist) the right one? - Eldereft (cont.) 20:24, 4 February 2009 (UTC)

Yes! Thanks. FX (talk) 03:58, 5 February 2009 (UTC)

## Nasa

Which formula does Nasa find most accurate when calculating orbits etc? —Preceding unsigned comment added by 86.135.98.182 (talk) 01:27, 9 April 2009 (UTC)

I do not know what they do, but I would guess that they use Parameterized post-Newtonian formalism with parameters which match General Relativity itself. But the general relativistic corrections are probably small compared to the corrections needed to deal with the Sun, Moon, and planets, and mass concentrations in the Earth (e.g. mountains), and special relativity. JRSpriggs (talk) 04:07, 9 April 2009 (UTC)

I thought I'd fix the blatantly incorrect capitals in section headings. But then I saw tons of cases of "displayed" TeX with no identation. Then I found a sentence that said "I'm not worrying about ${\displaystyle \lambda }$, it's discussed [later in the article]". Sigh........ Can someone be capable of understanding physics but at the same time think a sentence like that can belong in a Wikipedia article? How did such a long article manage to avoid the attention of anyone familiar with the basics of WP:MOS and WP:MOSMATH? I've put a "cleanup" tag on it. More work is obviously needed. Michael Hardy (talk) 22:27, 16 October 2009 (UTC)

### Just one example

I found this:

${\displaystyle {\begin{matrix}S_{S}=-\int d^{4}x\,{\sqrt {-g}}({1 \over G^{3}}(\textstyle {\frac {1}{2}}g^{\mu \nu }\nabla _{\mu }G\nabla _{\nu }G-V(G))+{1 \over G}(\textstyle {\frac {1}{2}}g^{\mu \nu }\nabla _{\mu }\omega \nabla _{\nu }\omega -V(\omega ))\\\ +{1 \over \mu ^{2}G}(\textstyle {\frac {1}{2}}g^{\mu \nu }\nabla _{\mu }\mu \nabla _{\nu }\mu -V(mu)))\end{matrix}}}$

I changed it to this:

{\displaystyle {\begin{aligned}S_{S}&=-\int d^{4}x\,{\sqrt {-g}}{1 \over G^{3}}\left({\frac {1}{2}}g^{\mu \nu }\,\nabla _{\mu }G\,\nabla _{\nu }G-V(G)\right)\\&{}\qquad \qquad +{1 \over G}\left({\frac {1}{2}}g^{\mu \nu }\nabla _{\mu }\omega \,\nabla _{\nu }\omega -V(\omega )\right)+{1 \over \mu ^{2}G}\left({\frac {1}{2}}g^{\mu \nu }\,\nabla _{\mu }\mu \,\nabla _{\nu }\mu -V(\mu )\right)\end{aligned}}}

Does Wikipedia's physics community regard things like this as not worth bothering with? In physics articles generally, there seems to be less respect for conventions such as WP:MOS and WP:MOSMATH than there is in Wikipedia generally. Michael Hardy (talk) 20:10, 18 October 2009 (UTC)

I think it's a case of "wanting to spend time on formatting" and "wanting to spend time on physics" and "knowing LaTeX" being three uncorrelated qualities. This isn't a problem if there are enough editors that cleanup eventually happens, but we're a bit understaffed :). By all means make an editing pass if you like, and by all means ask people at WT:PHYS to vet it afterwards if you feel it would be useful for them to do so. --Christopher Thomas (talk) 21:32, 18 October 2009 (UTC)

## Bitensor are more complex than GR

In the section Alternatives to general relativity#Classification of theories, the various types of metric theories are supposed to be listed from simplest to most complex. However, bitensor (η,g) theories are listed before tensor (g) theories (including GR) even though they are more complex than GR. JRSpriggs (talk) 13:49, 14 March 2011 (UTC)

## Minor error

Text uses eta, table xi, for "check for preferred location effects". At least I think that's the problem. Too stupid to try to change it. 200.104.177.67 (talk) 20:05, 19 January 2013 (UTC)

If you look at Parameterized post-Newtonian formalism, you will see that there are two different sets of parameters used. One of them includes η and the other ξ. Does that answer your question? JRSpriggs (talk) 22:26, 19 January 2013 (UTC)

## Why are quantum gravity and TOE's part of the lead?

They should not be. General relativity is understood to be theory that only works at distances large compared to the Planck length. To talk about general relativity or its alternatives is already to imply that we're talking about macroscopic distances, so an article about "alternatives to GR" should clearly mean theories that lead to different experimental consequences at observable scales. Quantum gravity theories/TOEs aren't "alternatives" to GR because GR doesn't make predictions for Planck-scale experiments. The rest of the text seems more or less wise to this fact, since I think they're only mentioned one other brief time. Im guessing this part of the lead should be rewrote to say something along the lines of what I just wrote. Isocliff (talk) 23:17, 26 April 2013 (UTC)

The lead merely mentions them to make it clear that this article does not cover them, and provide links to articles that do. Is that not just what you are asking for? Perhaps you should read the whole lead more carefully. JRSpriggs (talk) 06:44, 27 April 2013 (UTC)

## Merger proposal

It seems to me that the article on Modified models of gravity should be merged into this article. The "Modified models of gravity" article is very short, doesn't really contain any information that's not found in "Alternatives to general relativity", and is not in fact a different topic. The worst part of having two separate articles is that readers of one aren't necessarily aware of the other's existence -- looking for the article on Modified Gravity I came first upon "Modified models of gravity" and have only recently discovered that this much more detailed article exists. HFD90 (talk) 02:13, 24 October 2014 (UTC)

Yes, I agree and will do this soon if no one disagrees. Absolutelypuremilk (talk) 14:35, 6 December 2015 (UTC)
I have done this now Absolutelypuremilk (talk) 14:18, 14 December 2015 (UTC)

## Merger proposal with Jambalaya

It seems like a joke at first, but in fact this article is an abstract form of a Jambalaya of fringe items, incorrect items, unsourced meaningless statements, etc. So half seriously, should be done, and 80% of the material here removed. I am not really dead (talk) 19:01, 14 February 2016 (UTC)

It might be more helpful if you identified some of the incorrect items William M. Connolley (talk) 19:55, 14 February 2016 (UTC)
Yes, it would be helpful, but would be a very very long list. As a token, look at "Theories from 1917 to the 1980s" as a section. It is insane to lump over 70 years of rapidly changing physics together. Reflects a lack of understanding of the concepts. Unfortunately I do not have the time to do this, partly because I am not sure if it will survive the edits of some undergrad in 6 months. I will just leave it for whoever wants to spend the time. Sorry, I might be dead by the time I finish cleaning up the physics in Wikipedia.
By the way, a bigger problem is this one [1]. Misses the really key items. I am not really dead (talk) 21:24, 14 February 2016 (UTC)

## Rename

I'd like to recommend that this article be renamed. These theories aren't necessarily defined by General Relativity. My feeling is that they should be described as Contemporary Gravitational Theories, or something similar. That would do more to establish them as potentially viable, and make it clearer that these are gravitational theories. That also would allow the article to focus on the motivations for alternatives, rather than being list-like in nature. In other words, it would have a more coherent theme, and would give the article more direction. — Preceding unsigned comment added by 70.247.163.128 (talk) 21:05, 30 August 2016 (UTC)

I disagree - GR is pretty widely accepted and most theories are examined as ways to explain the few things that GR does not. However, it could be good to include gravity in the title, what about "Alternative gravitational theories to General Relativity"? Bit clunky unfortunately though! Absolutelypuremilk (talk) 21:49, 30 August 2016 (UTC)
Indeed, the current title does not suggest that these theories are necessarily defined by general relativity. On the contrary.
I don't think the addition of "gravitational" would be needed, as gravitation is automatically associated with general relativity. And clucky indeed . - DVdm (talk) 06:36, 31 August 2016 (UTC)