Talk:Gravity

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Former good article nomineeGravity was a Natural sciences good articles nominee, but did not meet the good article criteria at the time. There may be suggestions below for improving the article. Once these issues have been addressed, the article can be renominated. Editors may also seek a reassessment of the decision if they believe there was a mistake.
Article milestones
DateProcessResult
April 10, 2006Good article nomineeNot listed

Use Oxford spelling, December 2024, vs AmEng

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The Talk page says AmEng but the article says Oxford spelling? I think we should stick to AmEng. Johnjbarton (talk) 23:41, 8 December 2024 (UTC)[reply]

I reluctantly agree. I did not notice the talk page banner for American English when I made that edit. I picked Oxford spelling since it is most commonly used for science articles (e.g. Caesium) and I believe it should be used for all science articles. However, the AmEng banner was there for a longer time, so I agree that American English should be used instead of Oxford spelling. ZZZ'S 17:59, 9 December 2024 (UTC)[reply]
If there is no banner, you should use whatever style of English is most prevalent in the article.—Anita5192 (talk) 18:53, 9 December 2024 (UTC)[reply]
Well there is a banner. Johnjbarton (talk) 19:27, 9 December 2024 (UTC)[reply]
FWIW I'm not against Oxford if you develop a consensus to change. Oxford is not the most common nor does that matter one way or the other. Caesium is spelt that way because of an international standard, IUPAC. Johnjbarton (talk) 19:32, 9 December 2024 (UTC)[reply]
It's also the British and Oxford spelling, so... ZZZ'S 20:40, 9 December 2024 (UTC)[reply]
Sorry I was not clear. It is my opinion that the consensus to adopt Caesium is a consequence of IUPAC and not a consequence of common usage across science pages. Johnjbarton (talk) 00:57, 10 December 2024 (UTC)[reply]
You know what? Scratch the previous example. Jupiter would be a better example. ZZZ'S 01:13, 10 December 2024 (UTC)[reply]

Semi-protected edit request on 5 March 2025

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In the 'See also' section, in the line 'Gravitational biology – study of the effects gravity has on living organisms', the S on 'study' should be capitalised as all other words following a dash are capitalised. It is only a minor detail but one that I noticed. AT.folf (talk) 18:49, 5 March 2025 (UTC)[reply]

 Done —CX Zoom[he/him] (let's talk • {C•X}) 18:54, 5 March 2025 (UTC)[reply]

Definitions

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The term "gravity" is defined in the lead section and then redefined in a different way in the "Definitions" section. It is confusing. The material in the "Definitions" section needs to be better integrated. 2A00:23C8:7B20:CC01:38EC:880A:5420:3641 (talk) 20:39, 24 April 2025 (UTC)[reply]

Ouch. So gravity as a classical force is "that which we feel on Earth". The word "gravity" is also used for "gravitational force". Our content is messed up. For example gravitational force redirects to Newton's law of universal gravitation which isn't quite right as Einstein showed us. It will take some time so sort this out, thanks for the heads up. Johnjbarton (talk) 22:30, 24 April 2025 (UTC)[reply]
I agree the "Definitions" section is messed up, and probably should be removed. --ChetvornoTALK 05:36, 25 April 2025 (UTC)[reply]
I verified the content in that section against the source given, so simply deleting it would not be right. I think we need to address the different meanings directly. Johnjbarton (talk) 14:34, 25 April 2025 (UTC)[reply]
To add my humble opinion: There have been a lot of discussions on this page on whether to remove the term "force" from the article, since as you say it is technically incorrect. However Newton's law of universal gravitation which describes gravity as a "force" is an approximation still used in most of physics and engineering, and every high school physics textbook introduces gravity as a force. I think the article should explain that it is not really a force, but appears as a mutual force of attraction between everything in the universe with mass or energy (including light).--ChetvornoTALK 05:54, 25 April 2025 (UTC)[reply]
I agree. Johnjbarton (talk) 14:36, 25 April 2025 (UTC)[reply]

Proposed reorganization

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The current TOC places one of the most notable aspects of the topic, Earth's gravity, and two of the most interesting properties, radiation and speed, on the second level. I think the article would be more interesting and more useful in the following order

I think the History and the Einstein field equations sections should be shorter. Johnjbarton (talk) 00:03, 27 April 2025 (UTC)[reply]

I would caution against this. Currently the article up to the specifics section is a clear and chronological build up from simple and primitive notions of gravity up to complex and accurate understanding of GR. Going straight to the deep end with a fundamental interaction section won't help readers without any knowledge and it is precisely those readers who will look up an article as general as "Gravity". Except for the "Definitions" section which doesn't add much I think the material from the start of the article all the way to the subsection on the Einstein field equations should remain in the article and in the order it is now. Furthermore we don't actually know what the fundamental interaction of gravity is quantum mechanically speaking.
While I agree that a reorganisation could be of benefit here I have a counterproposal that I think might work a bit better. I particularly like your idea of creating sections for gravity on Earth and in astrophysics. I also like the idea of promoting the subsection "speed of gravity" to a main section since it is clearly a important feature of gravity. My suggestion would be:
  • Intro
  • Definition
  • Fundamental interaction (new)
  • History
    • Ancient world
    • Scientific revolution
    • Newton's theory of gravity
    • General relativity (expand with some of the subsection on the Einstein field equations)
  • Speed (was speed of gravity)
  • On Earth (was Earth's gravity)
    • Tides (new)
    • Gravity waves (new)
    • Measurement of the gravitational constant (new)
    • Gravity anomaly
    • Anomalies (new summary of Gravity anomaly + current Flyby anomaly) (These are not on Earth)
  • In Astrophysics (new),
  • Modern research
    • Mathematics of general relativity (most of the current Einstein field equations subsection)
    • Numerical relativity (new)
    • Tests of general relativity
    • Gravity and quantum mechanics (reversed order with tests of gr since this is more speculative, this way it's sorted from best to least known)
    • Alternative theories (absorb the material on the flyby anomaly, pioneer anomaly, extra fast stars, accelerated expansion here & remove redundancies)
ScienceDawns (talk) 09:54, 30 April 2025 (UTC)[reply]
I like your outline, but your version does not address the most important flaw in the article: the intro starts with fundamental interaction but never discusses it directly. Maybe we need to keep the Definition section.
We have plenty of sources to say gravitation is a fundamental interaction. I completely agree that Einstein's field equations should not be moved up. I'm talking about a qualitative paragraph outlining what is known.
I'll see if I can make progress on the parts we agree. Johnjbarton (talk) 17:56, 30 April 2025 (UTC)[reply]
I moved things around. Next would be some additional summary subsections.
I moved some of the lead into Definitions which improved the lead IMO. Take a look. Johnjbarton (talk) 17:54, 1 May 2025 (UTC)[reply]

History section undue

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Our treatment of the History of gravity is not appropriate: Galileo is mixed in with other much less notable names. George Gamow's book Gravity says

  • There are three great names in the history of man's understanding of gravity: Galileo Galilei, who was the first to study in detail the process of free and restricted fall; Isaac Newton, who first had the idea of gravity as a universal force; and Albert Einstein, who said that gravity is nothing but the curvature of the four-dimensional space-time continuum.

Johnjbarton (talk) 00:20, 27 April 2025 (UTC)[reply]

Indeed those three are by far the most important but we do have to be wary to not overly credit them either. It is easy to deify them because it is a nice story to describe the history of gravity as coming from three wise men while disregarding the many many shoulders they stood on. In the case of Galileo for example, he is often credited with the experiment of dropping balls of the tower of Pisa. The article correctly points out this is nothing more than legend and that Simon Stevin was the one to actually carry it out (although Galileo had already proven the universality of freefall by that point through other experiments and logical arguments). I would like to keep this sceptical attitude. ScienceDawns (talk) 10:00, 30 April 2025 (UTC)[reply]
Galileo did not prove the universality of freefall and his demonstrations at the tower of Pisa were actually taken to be evidence against it. (See Galileo's Daughter) The focus on the priority of the ball-dropping is what is wrong. Priority does not affect the course of history as much as mythological accounts make out, see Stigler's law of eponymy. Simon Stevin is a tree falling in the forest. Galileo is important not because of his demonstrations but because of his writing about the them. Johnjbarton (talk) 17:50, 30 April 2025 (UTC)[reply]

Undue discussion of Hooke.

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I think Hooke and even the priority dispute should be mentioned, but the current content is way out of whack. Even the main source for the content, the book by the Gibbons, says Newton is the Giant. They want to highlight Hooke and Halley by comparison:

  • Whilst Newton is widely regarded as one of the greatest scientists of all time, and the father of the English scientific revolution, John and Mary Gribbin uncover the fascinating story of Robert Hooke and Edmond Halley, whose scientific achievements neatly embrace the hundred years or so during which science as we know it became established in Britain. They argue persuasively that even without Newton science in Britain would have made a great leap forward in the second half of the seventeenth century, headed by two extraordinary men, Hooke and Halley.

Johnjbarton (talk) 23:01, 1 May 2025 (UTC)[reply]

I disagree. Hooke's contribution to gravity were extremely important (and famously known to Newton). Gribbin and Gribbin spend an entire chapter on Hooke's ideas on gravity. He specifically viewed gravitation as a universal attractive force. That seems like a significant idea in the history of gravitation, worthy of a paragraph here. Tito Omburo (talk) 17:16, 2 May 2025 (UTC)[reply]
Ok but we need a secondary source, not Hooke's own words, to identify what new ideas he proposed. Maybe it was universal attraction but its not clear. Kepler in 1609 talked about stones attracting stones. Johnjbarton (talk) 00:01, 3 May 2025 (UTC)[reply]
Gribbin and Gribbin is a good secondary source that includes the same quotation given here. Tito Omburo (talk) 11:13, 3 May 2025 (UTC)[reply]
Well we already have 4 sources that say Hooke said the things in quotes but none that say he said it first or in a way that otherwise influenced future work. Reporting a self-publication is not a review or secondary reference. At least some of what he says was common knowledge at the time according to historians. Johnjbarton (talk) 15:08, 3 May 2025 (UTC)[reply]
I mean, that's literally the point of the Gribbin chapter. It even makes a point of pillorying Newton's conception of gravity in the same historical period. Somewhat ironically, Newton's decidedly alchemaical view would ultimately win out, but only after the Hooke-Newton correspondences, rejection of the Aristotelean view of matter, together with Newton's unique mathematical genius. The "priority dispute", such as I understand it, was whether Hooke even had Newton's *inverse square law*, which to me it seems likely he did, but that's not what the article says and my opinion doesn't matter. Anyway, questions of "priority" or "meaning" in the 17th century episteme always seem highly problematic. A direct quote seems like the best solution here. Multiple secondary sources can be produced to show that it is an important quote. Tito Omburo (talk) 21:29, 3 May 2025 (UTC)[reply]
I agree that the multiple sources citing the direct quote is evidence of the notability of the quote.
Dugald Stewart includes the quote in his discussion "Indirect Evidence which a Hypothesis may derive from its agreement with the Phenomena" which I interpret as Stewart saying Hooke's unique contribution was to adopt a new approach, to make logical conjectures for comparison to experience, what we could call "predictions" in scientific theories now.
I made corresponding changes but it is difficult to express Stewart's ornate prose. Johnjbarton (talk) 23:31, 3 May 2025 (UTC)[reply]
Ok I found another modern but similar analysis of Hooke's role which I added. I have another issue but I'll start from the top of this thread. Johnjbarton (talk) 19:17, 4 May 2025 (UTC)[reply]
I'm satisfied with the Hooke content now, but it seems awkward to start a section entitled "Newton's theory of gravitation" with Hooke. Based on multiple sources, I would place Hooke at the end of the scientific revolution section. Johnjbarton (talk) 19:35, 4 May 2025 (UTC)[reply]

Image placement

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@ZergTwo I know that the image markup for an image related to a summary section might "logically" go after the section {{main}} tag, but this placement is visually awkward and disrupts the text flow. A summary section is typically short and its vertical space is often similar to the vertical height of the image. The section title and {{main}} summary line are typically horizontally narrow. By placing the image just before the section title, the top of the image uses the white space to the right of the title/main. In my opinion this looks better and it functions better because the image in the summary is less likely to push down on the image in the next section, making it look terrible.

I know there is no perfect solution to this issue. Every solution will fail in some cases. In my experience placement just before the section title is the best compromise for short sections in viewed in common browser widths. Johnjbarton (talk) 17:13, 17 May 2025 (UTC)[reply]

It will be horrible on mobile devices because the image for one section will actually be located at the end of the previous collapsible section. —CX Zoom[he/him] (let's talk • {C•X}) 18:58, 17 May 2025 (UTC)[reply]
Oh I see. How about above the {{main}}? Johnjbarton (talk) 21:07, 17 May 2025 (UTC)[reply]
Again, on mobile and thin screens image will be placed above the hatnote. But that wouldn't be a big problem, except that image usually appears after hatnote. —CX Zoom[he/him] (let's talk • {C•X}) 00:33, 18 May 2025 (UTC)[reply]
The images shouldn't be at the end of the section per MOS:ACCIM and MOS:SECTIONLOC. If the image spills into the next section, either expand the section where the image is located or remove the image. ZergTwo (talk) 13:49, 18 May 2025 (UTC)[reply]

Speculation/ambiguity

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The article makes the following claim in the intro:

  • Although experiments are now being conducted to prove (or disprove) whether gravity is quantum, it is not known with certainty.

Citing

  • Cartwright, Jon (May 17,2025). "Defying gravity". New Scientist. New Scientist Limited. pp. 30–33. {{cite news}}: Check date values in: |date= (help)

In my experience, New Scientist is not always a reliable source. It's a news magazine, not a scientific publication. Usually these news magazine are reporting on a publication but we don't know what publication that is this case.

The claim is ambiguous. I guess "it is not known with certainty" relates to "whether gravity is quantum" but that would not make sense. It is known for certainty that we don't know whether gravity is quantum. So maybe it relates to "experiments are now being conducted"? Actually that is more likely. As far as I know, the scientific consensus is that no experiment has been proposed that would make this distinction, let alone "prove (or disprove)" it. Such an experiment would be extraordinary and we should therefore require high-quality sourcing.

I don't think this speculation belongs in the article and especially not in the intro since this topic, an experimental confirmation, is not discussed in the article.

@Countercheck Johnjbarton (talk) 02:41, 31 May 2025 (UTC)[reply]

Good article?

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Should this article be nominated for Good article? Johnjbarton (talk) 02:47, 30 June 2025 (UTC)[reply]

Semi-protected edit request on 30 June 2025

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There's a typo in this page, in General relativity > Solutions. It says "The non-linear second-order Einstein field equations are extremely complex and have been solved in only a few special cases.[93] These cases however has been transformational in our understanding of the cosmos. Several solutions are the basis for understanding black holes and for our modern model of the evolution of the universe since the Big Bang.[41]: 227 "

The "has" in "These cases however has been transformational" is in singular while it should be the plural "have". "These cases however have been transformational" RiginPlay (talk) 13:38, 30 June 2025 (UTC)[reply]

 Done AlphaBetaGamma (Talk/report any mistakes here) 13:56, 30 June 2025 (UTC)[reply]

Speed of gravity

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This source and content based on it was recently removed as inadequately sourced:

Sure enough someone published a challenge:

This is nice analysis with good sources, concluding:

  • In summary, the gravitational field of the Sun is static. There is no propagation problem.

The orbits and effects of other planets are small perturbations on this static field. The 500s cycle observed in the erroneous paper was due to an error in coordinate systems. Johnjbarton (talk) 17:20, 30 June 2025 (UTC)[reply]

I didn't go as deep in my analysis; a mere glance at the source was sufficient to find several red flags. It is nice to see my crude analysis confirmed. —Quondum 18:25, 30 June 2025 (UTC)[reply]

Review of article

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I'm breaking this down into sections with numbered sub-points for ease of reference and editing. There are previous discussions along this line above, but I'm starting afresh. —Quondum 23:23, 30 June 2025 (UTC)[reply]

Article focus

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  1. Article topic
    • The topic of this article is presumably gravitation, the phenomenon of the interaction through long-range effects coupled to mass, and in GR, by extension to the stress–energy tensor. —Quondum 23:23, 30 June 2025 (UTC)[reply]
    • This is distinct from the topic of gravity of Earth, which the lead should make it clear is not the topic, and should relegate this to a section that makes it clear that this is an everyday consequence of gravitation, not treat it as an alternative topic as the lead does at the moment. —Quondum 23:23, 30 June 2025 (UTC)[reply]
      In the "article level" discussion below I gather you agree to an entry level broad topic article. From this point of view I don't think the intro should zero in one on definition and exclude others. Rather the various aspects covered in the article should be mentioned, including the fact that historic and geodesic "gravity" force is not identical with theory. Johnjbarton (talk) 18:09, 1 July 2025 (UTC)[reply]
      I'm in broad agreement. The lead can mention definition and manifestations (I regard experienced gravitational acceleration as the latter); I have tweaked the lead accordingly. —Quondum 19:16, 1 July 2025 (UTC)[reply]
      I dug out "The Character of Physical Law" by Richard Feynman. The first chapter is the "Law of Gravitation, an example of a Physical Law". This was a general audience lecture so the level matches our goals. (Ok a general audience keen to hear a physicist talk). Overall the topic he hits match the article, given 1964 era of the talk. He uses the phrase the "phenomena of gravity" which to me puts the focus on the physical effects. His writes down the inverse square law and proceeds to describe the consequences with little reference to the math. True he has only one paragraph on GR which mentions relativity as a small correction, but Black holes and cosmology were still new physics in 1964. I think this source backs up the direction we are heading. Johnjbarton (talk) 03:03, 4 July 2025 (UTC)[reply]
      Sounds like a good approach. The History section already mentions discovery of deviations of GR from Newtonian gravitation, but these should probably be covered as phenomena outside the History section. The list is quite long: gravitational time dilation, gravitomagnetism, different clock rates and orbit period when orbiting with and against planetary rotation, orbit precession, lensing, etc., so they may need to be covered only as multiple effects that are listed more thoroughly in another article. —Quondum 13:15, 4 July 2025 (UTC)[reply]
  2. Article level and readership
    • The article appears to be an entry (umbrella) article to the topic of gravitation, essentially an overview that can serve to answer first-level questions and direct people to more specific related articles. I am happy with it being pitched at this level. —Quondum 23:23, 30 June 2025 (UTC)[reply]
    • Are there competing umbrella articles? I have not found any during a very cursor check. —Quondum 23:23, 30 June 2025 (UTC)[reply]
      Yes, I think entry/summary article that is what we need for the topic. Shallow and broad, across whatever readers might connect to "Gravity". Johnjbarton (talk) 23:51, 30 June 2025 (UTC)[reply]
      We might not be thinking the same thing here: whatever readers might connect to "Gravity" is something that I'd like to avoid as potentially violating a WP policy (which happens to be one that I feel strongly about). For example, if the topic is gravitational interaction, then the statement Gravity, as the gravitational attraction at the surface of a planet or other celestial body, may also include the centrifugal force resulting from the planet's rotation is categorically disallowed in the definition. —Quondum 01:19, 1 July 2025 (UTC)[reply]
      I certainly don't want a dictionary entry nor to convert the gravity article to one on "gravitational interaction".
      To make my proposal in terms of a Wikipedia:Broad-concept article, the topics included should passes the "expert test" in the field of physics. We should not exclude topics called "gravity" that have reliable sources just because they do not fit into a single simplified point of view. The force of gravity between two test masses and the force of gravity in geodesy are both valid; they are both "gravity", they are closely related, and a physicist would not need training in another field to discuss these topics. Johnjbarton (talk) 03:02, 1 July 2025 (UTC)[reply]
      I think we're closer in approach than you realize. It is merely a matter of presentation and structure, not of coverage. I'll make some tweaks and you can see what you think. —Quondum 17:53, 1 July 2025 (UTC)[reply]
  3. Article title: If this article remains in introduction to or overview of gravitation, "Gravitation" and "Gravity" are both reasonable titles, bearing in mind that the level of formality is low as an overview. I would have preferred the former if a more formal tone was appropriate.
  4. Template inclusion
  5. Closely related articles (cursory scan) – some rationalization might be sensible:

Specific sections

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  1. Gravity § Definitions
    • This needs a complete rewrite. —Quondum 23:23, 30 June 2025 (UTC)[reply]
      For a broad-concept article I think we need a section in this location that briefly outlines the major aspects of gravity. Brief is important. I'm also ok if we can simply fold that goal into the intro, that is the best solution. Johnjbarton (talk) 18:20, 1 July 2025 (UTC)[reply]
      I'm thinking about how to do this. A concise definition that encompasses both that of Newtonian gravity and GR is a challenge. I would prefer to steer clear of mentioning the inverse-square law in a definition section. GR uses not only relativistic mass as a source (particle physicist should have their heads read for trying to redefine the term "mass"), it uses the entire energy–momentum tensor. Newtonian gravity also admits a term that is proportional to distance (ref Susskind), which leads to Hubble-like expansion. Treating gravity as a field-like phenomenon from the start rather than assuming the Coulombian least-quare-law law leads to a far more intuitive approach. Any feelings on this? —Quondum 18:58, 1 July 2025 (UTC)[reply]
      Let's change the name of the section instead, for exactly these reasons. We can't succeed because different sources will lead us to different aspects and into terminology and details that will be too steep for the entry level. (I agree that a field presentation simplifies classical/GR transition but is this the right place?) Johnjbarton (talk) 19:24, 1 July 2025 (UTC)[reply]
      This makes sense. We should try to capture in a general sense what we mean by gravity, but it need not be as precise as a "definition". Kind of "an effect that matter has in influencing the motion of other matter that is not mediated by other forces, and is connected to mass" thing. One could even name the section "Characterization". —Quondum 19:37, 1 July 2025 (UTC)[reply]
  2. Gravity § History
    I agree. When I first looked at the article the History was seriously out of balance. I added to correct this as I did not want to remove sourced content too quickly. I think merging most of this into History of gravitational theory and shortening to a summary is needed. Maybe @ReyHahn has an opinion on this aspect. Johnjbarton (talk) 18:13, 1 July 2025 (UTC)[reply]
    The article is of reasonable prose size (4k words). I don't think it is a problem that a broad topic has a long history section. That said, maybe either the rest of sections should be expanded or the history section shortened for balance.--ReyHahn (talk) 21:39, 2 July 2025 (UTC)[reply]
  3. Gravity § On Earth
    • This should be generalized and clear about surface gravity of bodies as being the observed effective acceleration resulting from the phenomenon of gravitation, maybe less specifically about Earth, and keep it very short. —Quondum 23:23, 30 June 2025 (UTC)[reply]
  4. Gravity § Astrophysics
    • This might need retitling, e.g. Astrophysical observations, but content is good (though I'd delete mention of the flyby anomaly as off-topic). —Quondum 23:23, 30 June 2025 (UTC)[reply]
  5. Gravity § General relativity
  6. More possible sections

Gravity in geodesy

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The removed content

  • Gravity, as the gravitational attraction at the surface of a planet or other celestial body may also include the centrifugal force resulting from the planet's rotation.

was based on

  • Hofmann-Wellenhof, B.; Moritz, H. (2006). Physical Geodesy (2nd ed.). Springer. ISBN 978-3-211-33544-4. § 2.1: "The total force acting on a body at rest on the earth's surface is the resultant of gravitational force and the centrifugal force of the earth's rotation and is called gravity.

We need to handle this in the article. We can disavow the geodesy definition, but in my opinion it would be better to confront the issue directly. As far as I am aware, all introductory physics courses treat the "force of gravity" as the thing that geodesy calls "gravity". That is, the "mgh" level of discussions ignore rotation as a pedological necessity. To me, the knowledge about "gravity" includes layers of increasingly accurate physical models. (That is why I would like avoid starting with gravity==gravitational force out of the gate as discussed above). Johnjbarton (talk) 19:42, 1 July 2025 (UTC)[reply]

It is reasonable to describe this composite effect of gravity and rotational acceleration as observed on the surface in a co-rotating frame; I see this as going into the above proposed generalization of Gravity § On Earth. In the article, we just give it a different name (e.g. gravitational acceleration) to avoid confusion. —Quondum 19:50, 1 July 2025 (UTC)[reply]
We could also take a slightly different tack: rename the article Gravitation, and reserve the name gravity to refer to the apparent force experienced by an object on the surface of a planet or similar. This comes across as being more formal, but that is okay in the context. Anything that allows a clear and non-awkward separation of the meanings should work. —Quondum 13:03, 4 July 2025 (UTC)[reply]

Converting History section to a summary

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Per discussions above I'm planning to replace the History section here with a two-paragraph summary of History of gravitational theory. First however I will merge all of the content here into that article which may take some time. Johnjbarton (talk) 15:38, 2 July 2025 (UTC)[reply]

mutual attraction

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Is this the best phrasing? I know this article is run by top notch science people (unlike me). But is the word "attraction" correct? Attraction seems to imply an attraction when it is not actually an attraction but per Einstein a behavior due to time-space curvature. Inayity (talk) 11:35, 28 July 2025 (UTC)[reply]

The first paragraph is less than great:
  • I concur that "a mutual attraction between" leans on the imagery of Newton's action-at-a-distance, which we need to move away from in the article; sources both feel and generate a gravitational field (which is a distortion of spacetime), not other sources.
  • "all massive particles" is also incorrect as a summary: for example, electromagnetic fields generate gravitational fields and would normally be termed "massless particles" or fields. Making a bit of leap, there should exist an orthogonal set of coordinates at each point that reduces the stress–energy tensor to diagonal form, edge cases excepted (local mass density and three orthogonal components of pressure). This means that up to a boost, I expect that a suitably accurate description of the sources should be described as mass (or energy) and pressure distributions. The contribution of pressure to gravity should not be glossed over: in a scalar source (such as dark energy), the gravitational repulsive effect of the negative pressure overwhelms the gravitational attractive effect of the positive mass density (by a factor of 3), leading to the very significant and well-known cosmic expansion.
This article seems to be about gravitational theories generally, so we do not need to phrase the first paragraph of the lead in terms of GR, but I certainly think that we should avoid biasing it to specifically Newtonian imagery. —Quondum 12:08, 28 July 2025 (UTC)[reply]
I've tried to tweak it. I tried to make it general to all theories of gravity, but that leave it feeling vague. —Quondum 13:16, 28 July 2025 (UTC)[reply]
It is not an easy thing to define. I have searched many places and they all muck it up-- even Nasa. The section on Characterization needs to make a distinction between Newton and Einstein because, and I might be wrong, it seems a little confusing. This lady explains it well [Cleo Abrams on Gravity is a lie]--Inayity (talk) 16:09, 28 July 2025 (UTC)[reply]
Sorry I completely disagree. The "attractive force of gravity" has been and is one of the most successful scientific theories of all time. The article includes numerous reliable sources to this effect. Phrases like "gravity is a lie" are just jingos to market discussions, not statements consistent with physics.
All physical models have advantages and disadvantages. Treating gravity via geometry is a powerful approach with many wide ranging and intriguing consequences. It is also extremely abstract and difficult to apply in simple scenarios.
I again encourage consulting notable sources designed for broad audiences like Feynman's lectures. He explains gravity via attractive force because it clearly acts that way from our perspective and it is a model with many, many solid predictions. Its failures are just as instructive. The same cannot be said for other models. Johnjbarton (talk) 17:31, 28 July 2025 (UTC)[reply]
I can see where Inayity is coming from. That section mixes statements from Newton's law of gravity with statements that apply to general relativity, without distinguishing, which makes it incorrect and confusing. "gravity is a lie" is a way to express the equivalence principle, in the sense of gravity as forcebeing a fictitious force, but is not intended to be taken literally. It is not different from "gravity is an attractive force", which is a starting place for discussion, but cannot be made rigorous, because is not fundamentally true either. Just to throw the fox amongst the chickens, the dominant force of gravity on large scales, that due to dark energy, is repulsive despite its source having positive mass density. —Quondum 17:43, 28 July 2025 (UTC)[reply]
Our current first sentence is
  • In physics, gravity (from Latin gravitas 'weight'), also known as gravitation or a gravitational interaction, is a fundamental interaction, which may be described as the effect of a field that is generated by a gravitational source such as mass.
In my view this fails to match the sources we use in the article. It is also circular and puzzling: a gravitational source generates gravity? But I don't think a tweak will fix it because such puzzles are fundamental to all theories.
We should treat gravity a physical phenomenon, not as the consequence of any necessarily incomplete theory. As a physical phenomenon we can point to many different manifestations, each of which can be modeled with theories of gravity to differing degrees of satisfaction. None of these theories are truth and there is no evidence that any theory will ever be truth. Theories organize facts and make predictions. Good simple theories make quick predictions; accurate predictions may need more complex theories. We need to summarize the main theories rather than pick one. Johnjbarton (talk) 18:45, 28 July 2025 (UTC)[reply]
The circularity should be avoided, agreed. However, giving specifically mass as the source is fine for Newtonian gravity, but is incorrect for GR (and for the real world, obviously). We are at liberty to recognize when sources make shortcuts in their definitions/characterizations rather than blindly following their wording. Finding a general way of encapsulating what gravity is that fits all current theories is of course difficult, but it seems to be necessary to define the type of source in some way to distinguish it from the other interactions. It might be reasonable to split this into "generated by mass, in Newtonian gravity, and stress–energy, in general relativity". Of course, this still references theories, but it is one way to sidestep the circularity. Another approach is to say that gravity is whatever is "really out there" and looks like Newtonian gravity in the Newtonian limit ...
To treat gravity as a physical phenomenon to which we match theories (and I would prefer this approach too), we need a top-level description/definition that is theory-independent. Do you think that we can find a source that defines it in this way adequately? I'm not holding my breath, though. —Quondum 19:21, 28 July 2025 (UTC)[reply]
I think characterizing gravity as a force of mutual attraction between masses is widely and reliably verifiable. I don't have access to many college textbooks now, but consider
  • Feynman, R. (2018). Feynman Lectures On Gravitation. United States: CRC Press. Section 1.2 "The Characteristics of Gravitational Phenomena", page 3, "First of all there is the fact that the attraction obeys the inverse square law." Note that this book is about general relativity and quantum gravity.
or
  • https://www.feynmanlectures.caltech.edu/I_07.html What is this law of gravitation? It is that every object in the universe attracts every other object with a force which for any two bodies is proportional to the mass of each and varies inversely as the square of the distance between them.
Thus mutual attraction at the inverse square distance is the most notable and salient characteristic of gravity according to Feynman. Is there any comparable source which claims otherwise? Johnjbarton (talk) 17:18, 30 July 2025 (UTC)[reply]
You seem to want to rely heavily in the Feynmann Lectures, rather than drawing on a wider group of references, such as MTW. The Feynmann Lectures were pitched at a level that requires extensive qualification, meaning that quotes from it cannot be used in isolation. Feynmann's intention was to build a basis of intuition and understanding for newcomers to the subject, to be elaborated with all the caveats and subtleties of the reality later. I would disqualify it on these grounds for the purpose here, which is not pedagogical and should make sense at all levels. Feynmann's Gravity is the law that every object with mass attracts every other object in the universe in proportion to each mass and inversely proportional to the square of the distance between them. is flat-out wrong except in Newtonian theory, and Feynmann would have been first to admit it. Even the idea of "distance" needs qualification. (What is the distance from a black hole, the quintessential gravitating mass? It is not measurable along a path to its centre, but has to be defined in terms of the area of an enclosing surface.) This article's The electromagnetic force law is similar to the force law for gravity: both depend upon the square of the inverse distance between objects in typical interactions. is also an oversimplification: typical magnetic interactions have an inverse-cube law. If we use invalid oversimplifications, at least we should be clear that we are doing this. I would suggest that a better approach would be to characterize gravity as the phenomenon that reduces to the inverse-square law in suitable configurations. But a review of characterizations by other, less pedagogical sources might make most sense. —Quondum 18:49, 30 July 2025 (UTC)[reply]
I'm puzzled by your reply. I guess you are imagining some plan I don't have. I was just replying to the original claim.
MTW is a graduate text in general relativity: it presumes that readers are already trained in Newtonian gravitation and aware that the predictions of that model are spectacularly accurate in most circumstances. Readers of this article should be made aware of that success and the model behind it. These results are notable aspects of gravity just as much as black holes.
The article already discusses general relativity and I am not proposing to remove it. I am not proposing to replace the article with Feynman's pedological approach. I am only citing Feynman as an outstanding example of many, many explanations of gravitational phenomena based on Newton's model. I can provide a boat load of examples when I can get to a library.
Of course we should explain the few but important and interesting cases where Newton's gravity fails. However, every single one of those cases, with no exceptions, involve mutual attraction of objects. So I cannot agree with the opening post. I hope I am clearer now. Johnjbarton (talk) 00:15, 31 July 2025 (UTC)[reply]
It is becoming clear that we do not see eye to eye on what is suitable in WP. Separately, we also seem to be talking past each other (not seeing or accepting the other's meaning): a communication issue. This makes collaboration problematic. —Quondum 00:44, 31 July 2025 (UTC)[reply]
Yes, I was thinking the same. Johnjbarton (talk) 00:50, 31 July 2025 (UTC)[reply]

Minor edit

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Under "Einstein's general relativity", the first sentence of the third paragraph should read "The principle of relativity...*led* [emphasis mine] to a long and fruitless search..." I can't make the change due to the protection on the article. Bporterreporter (talk) 05:47, 30 July 2025 (UTC)[reply]

Fixed, thank you. MichaelMaggs (talk) 06:39, 30 July 2025 (UTC)[reply]

Semi-protected edit request on 17 August 2025

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Gravity is the phenomenon by which mass and energy cause a curvature in space‑time, guiding the motion of objects along that curvature, which in the Newtonian limit appears as a mutual force of attraction between masses proportional to the product of their masses and inversely proportional to the square of the distance between them. — Preceding unsigned comment added by Lolahe99 (talk • contribs) 12:42, 17 August 2025 (UTC)[reply]

It is not clear what you want.—Anita5192 (talk) 15:55, 17 August 2025 (UTC)[reply]