Talk:Gravity

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So should the article call gravity a force or not?

I know there has been some discussion to remove references to gravity being a force, as it isn't a force according to general relativity. Why, then, does paragraph 3 refer to the fundamental forces and the strong force, when in fact those (redirected) articles are properly called Fundamental interaction and Strong interaction? Seems like this would be confusing to the reader who isn't sure what exactly gravity is. -Jordgette [talk] 14:03, 1 July 2019 (UTC)

The use of "force" is per Einstein-Cartan Theory, endorsed by Einstein thru written conversations with Cartan, about 14 years after Einstein's publication of General Relativity, and well before his loss to Bohr in the EPR Paradox discussions of the mid-1930's. ECT accomodates the concept of particulate spin (discovered in the mid-1920's), and GR can reportedly be derived from it, per the last (Version 26) Arxiv preprint of an article by Petti, subsequently published. It is widely reported to be more sophisticated (mathematically) than GR, and has allowed elimination of the cosmic "singularity", as described by Nikodem J. Poplawski in numerous papers preprinted on Arxiv between 2010 and 2020, several of which were subsequently published. The addition of Einstein-Cartan Theory to the list of active (not historical) "theories of gravity" is essential to the plausibility of the Wikipedia article "Gravity", and its current absence from that list renders the entire article questionable. — Preceding unsigned comment added by Ole Berson (talk • contribs) 15:52, 11 August 2020 (UTC)

A very interesting article is here on the matter of the matter

Nature Astronomy, 2019. DOI: 10.1038/s41550-019-0823-y Darwinerasmus (talk) 14:48, 14 July 2019 (UTC)

With link: Realistic simulations of galaxy formation in f(R) modified gravity. It is nice that it makes a testable prediction. We'll see what happens, for now it is still one of the more obscure approaches. --mfb (talk) 10:46, 15 July 2019 (UTC)

Yes, we should discuss it as both and make an important distinction between when it is applicable. Both frameworks of Newtonian gravity (using Newton's law) and General Relativity are import and valid ways to describe the effects of gravity. In many instances, only describing interactions with Newtonian gravity as a force is sufficient. i.e. you don't really need GR to describe what happens to a trajectory when you throw a rock out of a window. Additionally, you can describe a lot of large-scale structure formation in the universe with only Newtonian gravity Cosmojellyfish (talk) 21:18, 7 January 2020 (UTC)

I propose to clarify. There are no gravitational forces as such. Those forces that are called gravitational are forces of inertia, reactions from the forces of expansion of the Universe. The forces of inertia and "gravity" are a reaction from a combination of gyroscopic forces of rotation of electrons. Read the collection of articles "Physics of Gravity" published by Morebooks. Colnago2253 (talk) 19:17, 25 December 2020 (UTC)

Wikipedia is not the place to publish original research. -Jordgette [talk] 20:07, 25 December 2020 (UTC)

This requirement does not apply to talk pages Colnago2253 (talk) 13:01, 26 December 2020 (UTC)

Talk pages are there to improve the article. They are not the right place for OR either. --mfb (talk) 05:04, 27 December 2020 (UTC)

I briefly expressed my opinion on the topic, about article. Colnago2253 (talk) 07:55, 27 December 2020 (UTC)

Semi-protected edit request on 11 December 2020

I think we should also add gravity as part of a series on General Relativity. 2405:201:600B:C84A:782F:D93E:EC23:F5D1 (talk) 12:23, 11 December 2020 (UTC)

 Already done. See Gravity#General relativity. ◢  Ganbaruby!  (Say hi!) 12:35, 11 December 2020 (UTC)

Fundamental force

1. Gravity is fundamental, not a consequence of anything else

I'm no expert on Wikipedia or physics but isn't this wrong or at best misleading: "describes gravity not as a force, but as a consequence of masses moving along geodesic lines in a curved spacetime caused by the uneven distribution of mass." Gravity is not a consequence of anything. It is one of the four fundamental interactions known to physics, meaning it is not (so far as we now know) reducible to anything else. Gravity is our description of the attraction between masses, and curved spacetime is at best a consequence of that attraction. A further point related somehow to that: Does gravity curve spacetime or make masses move along the geodesic lines of curved spacetime mentioned here? No, not if spacetime is only another of our descriptions of something, a construct of the imagination by which we attempt to understand the movement of masses. If I'm sketching a face and erase a line and redraw it more accurately, has that face changed my sketch? No, and can gravity curve spacetime in any other sense? In any case Einstein made gravity more fundamental, not less, and made space and time less fundamental, more contingent than Newton had. In short: gravity may have many consequences and effects, but is never itself a consequence or effect. This line might better say, for example: "describes gravity as the fundamental attraction between masses by which masses seem to move along the geodesic lines of a curved spacetime." Oop, need to sign this, don't I? John Hicks, logged on as JohnOnlineHicks, or John Hicks (talk) 16:12, 20 May 2021 (UTC) if that tells something more.

But modern physics doesn't describe gravity as a fundamental attraction. It describes the apparent attraction between masses as a consequence of spacetime curvature. I think the fundamental/irreducible aspect is that mass–energy and spacetime curvature are linked, although we don't know the mechanism of this linkage, whether it is directly causal, etc. I've heard a lot of people say that "gravity curves spacetime" but it's more like the other way around. Saying that gravity curves spacetime is a bit like saying that darkness extinguishes photons. -Jordgette [talk] 18:06, 20 May 2021 (UTC)

Hi Jordgette: If you're right then the Wikipedia article on fundamental interactions is wrong: "There are four fundamental interactions known to exist:[1] the gravitational and electromagnetic interactions, which produce significant long-range forces whose effects can be seen directly in everyday life, and the strong and weak interactions, which produce forces at minuscule, subatomic distances and govern nuclear interactions." As I understand this, the attraction between masses is fundamental, not a side effect of something else. A separate question: What do we mean when we say that attraction between masses ("gravity") curves spacetime, not the other way around? Does our own loose talk deceive us if we say gravity curves the path by which light travels? Gravity bends the light, not some path. Observing this and attempting to predict it, we construct a path. There are no paths among the stars. In short: the attraction (or interaction) between masses is fundamental and cannot (so far) be further reduced to a side-effect of something else, including in this case spacetime, whatever that may be. Right? — Preceding unsigned comment added by JohnOnlineHicks (talk • contribs)

If you continue on to the second paragraph at Fundamental interaction, you will find: "The gravitational force is attributed to the curvature of spacetime". There is no contradiction between the two articles. That an interaction is fundamental does not mean that it can't be attributed to (or caused by) something else. It is not an issue for gravity to be a consequence of curved spacetime, just as it is not an issue that the strong force is a consequence of interactions with gluons. - MrOllie (talk) 23:36, 20 May 2021 (UTC)

Thank you, MrOllie, but I'm still not clear on this. If "fundamental does not mean that it can't be attributed to (or caused by) something else" then what meaning is left for it? As the article Fundamental interaction defines it, "In physics, the fundamental interactions, also known as fundamental forces, are the interactions that do not appear to be reducible to more basic interactions." Said another way, they cannot by explained as effects of other causes, wouldn't you agree? Then in some loose sense we can say that gravity bends spacetime but not the other way around, not even loosely, and this much we can know without deciding what to make of spacetime? John Hicks (talk) 01:35, 21 May 2021 (UTC)

Hi John, I'll add by elaborating on a couple of your points. Gravity bends the light, not some path - The path through curved spacetime does bend the light, as seen by observers along the path. There are no paths among the stars - There is a geometry of spacetime among the stars. Light travels straight lines (geodesics) through that geometry. Gravity just is the geometry, like how the coming-together of longitude lines as you go toward the poles just is the geometry of Earth. It's counterintuitive because time is one of the four spacetime dimensions, and we're only used to thinking of geometry as lines in three dimensions of space. -Jordgette [talk] 00:45, 21 May 2021 (UTC)

Thank you for your gluon example, MrOllie, to help clarify spacetime. These particles are at first hypothetical. Here, hypothetical explanations of the strong force, another of the four fundamentals alongside gravity. "Soon after the postulation of quarks, it was suggested that they interact via gluons, but direct experimental evidence was lacking for over a decade." The gluon was at first only a useful unit of measure in that exchange. Doesn't spacetime serve a similar purpose in our attempts to measure and predict gravitational effects? Not an explanation of them, only a method of predicting them? Much of quantum physics still struggles with the difference, and successfully predicts more than it can explain. Isn't spacetime geometry just a hypothesis we had wrong for centuries, while gravity, being fundamental, marched on with or without explanations from us?John Hicks (talk) 01:36, 21 May 2021 (UTC)

Sorry to be tiresome, but how can we leave this sentence in its current form? One way we might simplify this question, for ourselves and Wikipedia readers? Step back from the physics and look at the language here, the shape of the sentence in question and the words it uses. "...the general theory of relativity (proposed by Albert Einstein in 1915), which describes gravity not as a force, but as a consequence of masses moving along geodesic lines in a curved spacetime caused by the uneven distribution of mass." 1. First, terminology: Is light a consequence of electromagnetic radiation within a certain range of the electromagnetic spectrum? No, just another name for it. Just as we now know, thanks to Einstein, that gravity is just another name for the fundamental attraction between masses. Nevermind that we misused the names light and gravity for centuries. 2. Would we say light is a consequence of charged particles moving in narrow range of frequencies caused by uneven distribution of charged particles? No. Light is a synonym here, not a consequence. But haven't we said the equivalent about gravity? Made one synonym the consequence of another, with an intermediate step obscuring the mistake? 3. Our sentence has A (gravity) a consequence of B ("masses moving along geodesic lines in a curved spacetime") which is in turn caused by C (uneven distribution of mass). That makes A (gravity) highly derivative, at the end of a sequence of consequences. What causes C to lead this parade? Why do those unevenly distributed masses (C) move at all? As a consequence of what? Do they spy geodesic lines under their feet, as actors find their marks on a stage? No, masses move because they are drawn to one another for reasons we cannot (so far) trace further. That attraction is not, so far as we know, a consequence of anything else. For lack of any further explanation we call this attraction fundamental, which puts it alongside electromagnetics (including light) on a very short list of four fundamentals. Another name for this fundamental attraction? Gravity. Now the loop in our sentence surfaces and comes into view: Gravity (A), which is the attraction between C (unevenly distributed masses), causes B (their movement of some puzzling kind), which then causes A (gravity). Our sentence cannot be right in this form. A clearer form would leave less room for error. 4. Simpler still, ask yourself this: if gravity is a consequence of curved spacetime, what is curved spacetime a consequence of? What bent it? What curved it? Not the uneven distribution of masses. Such masses might have kept to their same places forever if not for some attraction between them. What attraction? Gravity, AKA the fundamentally inexplicable attraction between masses. 5. Couldn't we fix this sentence by (in a way) reversing it? Newton made space and time fundamental and made light and gravity their captives. We perpetuate a trace of Newton's error if we make gravity a consequence and curved spacetime its cause. Einstein reversed this, describing gravity as a fundamental and inexplicable attraction between masses, and the apparent curving movement of those masses (including even light) as a consequence. How about something like this? describes gravity as the fundamental and inexplicable attraction between masses by which, in the near vicinity of other masses, they seem to move along geodesic lines in a curved spacetime.John Hicks (talk) 17:49, 21 May 2021 (UTC)

No, you've got it backward. If you accept that the Einstein field equations are accurate (virtually every physicist does), this is very 'explicable.' What we perceive as an attraction in 3 dimensions is not truly an attraction at all, it is just an object moving in a straight line through a curved spacetime. There is no reason to change the article to sound like this is in doubt by adding wiggle words like 'seem to' or the flatly incorrect 'inexplicable' - MrOllie (talk) 18:20, 21 May 2021 (UTC)

John, if you can find some reliable sources agreeing with you that in context of general relativity, the attraction between masses is fundamental, then you might have something. But I really doubt you will find reliable sources saying that, so unless you can point us to some, you're wasting your time and ours. -Jordgette [talk] 19:41, 21 May 2021 (UTC)

I think this is mostly just an argument caused by differing usages of the word 'gravity'. Words are important, of course (although John Hicks wall'o'words above is WP:TLDR). In general I agree with Jordgette and MrOllie, the existing text is adequate:

• I disagree with Jordgette that "...mass–energy and spacetime curvature are linked, although we don't know the mechanism of this linkage...". As MrOllie said they are linked through Einstein's field equations. Gravitation is as well understood as any of the other forces, and perfectly well enough to describe unambiguously in our article.
• In Newton's theory, the term 'gravity' had a single meaning, it was a force between masses. So you could say things like "the gravity of a mass attracts other masses".
• In GR, gravitational attraction is no longer considered a 'force', in the same sense as the Coulomb force between charges is. As Jordgette implied, masses influence each other's motion, but they do so indirectly through an intermediary, the spacetime metric. So our article avoids saying masses exert force on each other, or 'attract' each other. This gets a little awkward syntactically, so I wouldn't mind limited use of the phrases 'apparent force' or 'apparent attraction' in the intro.
• As a result in GR the word 'gravity' has become slightly ambiguous, it covers two different processes: the curvature of spacetime by mass, and the tendency for masses to follow geodesic world lines. We should be more careful about using it. What does "gravity curves spacetime" mean? It should be replaced by the more precise: "mass (or mass-energy) curves spacetime".
• "Gravity is one of the four fundamental interactions in physics" is supported by numerous sources and has to be in the article. It's an example of the proper use of the word. Here 'gravity' means the whole theory of gravity, the general theory of relativity.
• The sentence "The general theory of relativity... describes gravity not as a force, but as a consequence of masses moving along geodesic lines in a curved spacetime caused by the uneven distribution of mass." seems good enough to me.

--Chetvorno^TALK 04:30, 22 May 2021 (UTC)

Thank you all.

I hope I have not wasted yours or anyone's time, Jorgdette.

I took extra time over this because an article explaining Einstein is a good (tough) test for the Wikipedia approach. I still believe we need to clarify our explanations, but I don't have the expertise we need.

Sorry for my clumsy attempts at formatting here.

Time for me to revisit my library and see why I imagined gravity as fundamental rather than a consequence.

If my "inexplicable" goes too far, MrOllie, how about "not reducible," as the Wikipedia article on these four fundamental interactions says?

That article also calls them "fundamental forces." Better, isn't it? Interactions sounds like a cop-out, a fuzziness that allows circular reasoning to go undetected. We have not explained an interaction until we explain the forces within it, back and forth, in sequence.

Thank you, Chetvorno, for this: "masses influence each other's motion, but they do so indirectly through an intermediary, the spacetime metric." I'm eager to chew on that and see what I've missed, why I still smell a loop, and why this metric reminds me of the luminous aether Einstein blew away, a medium for the propagation of light.

Can't agree, though, with your definition of gravity as "the whole ... general theory of relativity." Says our Wikipedia article on the four fundamental interactions: "Second, gravity always attracts and never repels." Here gravity cannot mean the whole of Einstein's theory.

Is gravitation mediated?

More mysteries await us: "Merging general relativity and quantum mechanics (or quantum field theory) into a more general theory of quantum gravity is an area of active research. It is hypothesized that gravitation is mediated by a massless spin-2 particle called the graviton." Not by "an intermediary, the spacetime metric"?

Also from Wikipedia on the four fundamental interactions: "The modern (perturbative) quantum mechanical view of the fundamental forces other than gravity is that particles of matter (fermions) do not directly interact with each other." But in gravity they directly interact?

John Hicks (talk) 08:38, 23 May 2021 (UTC)

"Interaction" is preferred in particle physics as the interactions are not necessarily acting like classical forces. That's particularly important for the weak interaction. I'm not really sure what the point of the rest of your very long comment is. --mfb (talk) 09:05, 23 May 2021 (UTC)

Britannica: As the American theoretical physicist John Wheeler put it, matter tells space-time how to curve, and space-time tells matter how to move.

I was wrong in two ways and apologize. 

1. yes, spacetime mediates between masses; masses interact by deforming spacetime, not instantaneously across great distances. 2. this loop is simply an interaction, not circular reasoning

I once knew this! My example: If my tiny daughter and I plop down on a flimsy mattress to read a bedtime story, my weight makes a depression in the mattress that tumbles her into me. I have not pulled her. I have only moved her indirectly, by moving the mattress under us both.

Would the sentence I questioned be clearer this way? "...shows that gravity only appears to be a force where actually a mass moves along a geodesic line in a spacetime curved by other masses."

How reconcile this and the Wikipedia article on Fundamental Interactions? There gravity is a force, an attraction between masses ("always attracts, never repels"), much the way Newton left it.

Similarly the Britannica article on gravity talks at great length about Newton and less about Einstein: "The prime example of a field theory is Einstein’s general relativity, according to which the acceleration due to gravity is a purely geometric consequence of the properties of space-time in the neighbourhood of attracting masses." Is gravity as a force purely illusion then?

Should the two Wikipedia articles leave a middling scholar like me wondering: How then does mass deform or curve spacetime? Not by attraction, eh? And not by attraction between masses, unless spacetime has mass?

Britannica is also vague: "Space-time is a four-dimensional non-Euclidean continuum, and the curvature of the Riemannian geometry of space-time is produced by or related to the distribution of matter in the world." Produced how? Related how? Only some very advanced math can account for it.

Not saying either article is wrong, only speaking as a reader for whom their overlap could and maybe should be more clearly reconciled.

Have my comments here been useful?

John Hicks (talk) 16:27, 23 May 2021 (UTC)

Thoughtful views and feedback like yours are always important and useful for seeing how the article is deficient. I agree the article wording can probably be improved, but this is an inherently difficult, esoteric subject. I haven't seen any changes that I think are clear improvements yet:

• The term "fundamental force" is a widely used traditional term and we're kind of stuck with it. Gravity along with the other 3 forces is considered "fundamental" not because it is simple but because it is not due to more basic forces. "Force" is a good descriptive term because all 4 act as forces, but physicists prefer "fundamental interaction" because each is more complicated than a simple "force", altho it is difficult to explain how. The 3 other forces: strong, weak, and electromagnetic, are actually quantum fields; at the tiny quantum level there is no such thing as a "force" and they act by exchanging particles carrying momentum.

• For example, a magnet lifting a piece of iron is an example of the electromagnetic interaction. The magnet creates a magnetic field, which exerts force on the iron. But on a quantum level it can alternately be described as the atoms of the magnet and iron exchanging particles called virtual photons, which carry the force.

• Gravity is not considered a force for a different reason, because it acts by altering the geometry of spacetime. Your analogy of your sagging mattress creating an apparent force between bodies is on point. The article tries to illustrate this with the widely-used diagram of a planet creating a depression in a rubber sheet that is meant to be spacetime [1]. I like your Wheeler quote: "Matter tells space-time how to curve, and space-time tells matter how to move"; I think that could be in the article.
• I'm not sure what you mean by: "Second, gravity always attracts and never repels. Here gravity cannot mean the whole of Einstein's theory." Einstein's general theory of relativity is the accepted standard theory of gravity. It duplicates all results of Newton's theory to high accuracy. As far as I know (unless we are talking about exotic modifications like the cosmological constant) the general theory of relativity always results in attractive "forces" between masses, not repulsive ones.

--Chetvorno^TALK 21:26, 23 May 2021 (UTC)

Thank you, Chetvorno. "Gravity always attracts and never repels." A quote from Wikipedia, Fundamental Interactions. You're right, my comment could have been clearer: "In this sentence, used this way, gravity cannot mean the whole of Einstein's theory." John Hicks (talk) 11:53, 1 June 2021 (UTC)

Before we leave these questions behind:

I am not the first or only reader who comes to Wikipedia to refresh what I once studied.

What did the job for me: Britannica.

Consider the unreconciled differences between the responses to my questions here:

Jordgette was wise to say that the way mass curves spacetime is not well understood. I would be wise to quote her, not paraphrase.

MrOllie and Chetvorno cannot mean what they reply, that "they are linked through Einstein's field equations." The mechanisms of gravity worked long before Einstein or his equations.

Quantum physics carefully distinguishes what we can calculate (more) from what we can explain (less).

We don't want to confuse the two mechanisms: the mechanism we study and the mechanism by which we study it. Here, spacetime. We speak of spacetime both ways and risk a muddle. We risk making spacetime the new luminous aether, a medium for propagating all that we don't yet understand.

Britannica: "the acceleration due to gravity is a purely geometric consequence of the properties of space-time in the neighbourhood of attracting masses." Purely geometric? Merely geometric? Merely appearance? Merely illusion? Surely gravity worked just as well before any human could teach it geometry?

Chetvorno wisely recommends "apparent force" or "apparent attraction."

Maybe the problem is that word "consequence." We can mislead ourselves with it. A physical process has two kinds of consequence: physical consequences and consequences for our understanding. What was the flat earth a consequence of? Human misunderstanding. Maybe "implication" instead of "consequence" to warn that our understanding may be incomplete or wrong?

Can we clearly state what we do and do not know, each of us? "We" can mislead as well. Who is we? How many of us can speak for everyone? Not many. The surest of all answers: I'm not sure.

Grateful to you all for your responses, your expertise, and your efforts to understand and explain for us all. John Hicks (talk) 11:53, 1 June 2021 (UTC)

Semi-protected edit request on 23 May 2021

Change the link light (in the lead) to electromagnetic radiation (as it does not just refer to visible light). Preferably use a WP:PIPED link ([[electromagnetic radiation|light]]).108.46.173.109 (talk) 01:23, 24 May 2021 (UTC)

Done. --mfb (talk) 10:51, 24 May 2021 (UTC)

"At present"

@Chetvorno: The statement "Gravity is most accurately described by the general theory of relativity" gives the erroneous impression that the general theory is incapable of being replaced by something more general, tomorrow or in a thousand years, which is untrue.

I mean, suppose the year is 1800. Should we write "Gravity is most accurately described by Newton's law of universal gravitation"? Knowing what we know now, we know that is not true. Can we confidently say that 100 years from now, General Relativity will still be the most accurate description of gravity? No, we cannot.

Science is not a set of true statements, it is a set of statements that have, so far, not been proven false. I think you see what I am driving at, and why I think this statement can be improved. Perhaps "To date, the most successful description of gravity is given by the general theory of relativity". If you have a better idea, please implement it. Regardless, I will not edit this article again on this point unless we have agreement. PAR (talk) 19:45, 26 May 2021 (UTC)

By that logic we should add 'At present' in front of any scientific statement in the encyclopedia. - MrOllie (talk) 20:25, 26 May 2021 (UTC)

Agree with MrOllie, this is inconsistent with the rest of WP scientific articles, and misleading for general readers. It is understood that science is an ongoing discipline and scientific theories may be replaced by better ones in the future. We don't preface every WP article on a scientific theory with "at present". So the implication of inserting it here is that there is some other gravity theory which is about to replace general relativity in the near future. Although there is plenty of research on quantum gravity theories, none are anywhere near ready to replace GR. --Chetvorno^TALK 21:04, 26 May 2021 (UTC)

Agree with MrOllie and Chetvorno too. Gravity is indeed most accurately described by the general theory of relativity, and more accurately than by Newton's theory, which, more than 100 years ago, described gravity most accurately. The latter did not imply anything about now, as the former does not imply anything about the future. - DVdm (talk) 21:34, 26 May 2021 (UTC)

We don't need to put "at present" in front of every scientific statement and article, only the ones that phrase it in a way that suggests that a final truth has been found. The whole paragraph is sort of a historical account of Newton's theory being superceded by Einstein's theory, which is more general and accurate. What about something like:

Newton's law of universal gravitation was the first scientific description of gravity, which described gravity as a force causing any two bodies to be attracted toward each other, with magnitude proportional to the product of their masses and inversely proportional to the square of the distance between them. The general theory of relativity (proposed by Albert Einstein in 1915), is a more accurate and general theory of gravitation, which is essentially equivalent to Newton's law for non-relativistic situations. General relativity describes gravity not as a force, but as a consequence of masses moving along geodesic lines in a curved spacetime caused by the uneven distribution of mass. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon.

Note that no "at present" statement is needed. Everyone seems to at least understand my objection, so I will leave it at that. PAR (talk) 09:35, 27 May 2021 (UTC)

Your sentence: "The general theory of relativity (proposed by Albert Einstein in 1915), is a more accurate and general theory of gravitation..." falsely implies that there are other equally accurate theories of gravitation. --Chetvorno^TALK 15:08, 27 May 2021 (UTC)

No, I cannot agree - "Saturn is larger than Mars" does not imply that there are other equally sized planets. It simply means that Saturn is larger than Mars. It does not imply that Saturn is the largest planet. Maybe it is, maybe it isn't. The above statement concerning gravitational theories simply means what it says. Can you say with confidence that the general theory of relativity will never be subsumed by a more accurate and general theory? No, you cannot. To say that general theory is the most accurate description of gravity leaves the reader hanging. The most accurate possible? The most accurate so far? The most accurate known? All I'm saying is let's be clear. PAR (talk) 02:06, 28 May 2021 (UTC)

On second thought, I sort of see your point. It doesn't imply other equally valid theories, but it leaves that question open. How about "Newton's law of gravitation has been superseded by the general theory of relativity (proposed by Albert Einstein in 1915), which is a more accurate and general theory of gravitation, and is essentially equivalent to Newton's law for non-relativistic situations.PAR (talk) 03:23, 28 May 2021 (UTC)

No, the correct analogy would be if our article on the planet Jupiter were to say "Jupiter is one of the largest planets in the Solar System" instead of "the largest". --Chetvorno^TALK 05:29, 28 May 2021 (UTC)

Do you think the above restatement corrects the problem?

While I doubt a solar planet larger than Jupiter will be found, I have little doubt that a more accurate and comprehensive theory of gravity will be found, maybe a hundred years from now, maybe a thousand. Any suggestion that the general theory of relativity is the final word on gravity should be avoided. I think the above restatement reflects the present supremacy of the general theory without implying that it is the final truth. PAR (talk) 18:07, 28 May 2021 (UTC)

I agree with Chetvorno, we should not be trying to 'future proof' the article against possible revolutions in science. Also The "essentially equivalent to Newton's law for non-relativistic situations" isn't great. Newton's law gets the orbit of Mercury wrong, for example, and that isn't a relativistic situation. The article's current "for most applications, gravity is well approximated by Newton's law" doesn't have this problem. - MrOllie (talk) 18:19, 28 May 2021 (UTC)

The precession of the orbit of Mercury is most certainly a relativistic effect, basically because gravity propagates at the speed of light, rather than instantaneously as in Newton's theory: To quote from the Wikipedia article Tests of general relativity:

In general relativity, this remaining precession, or change of orientation of the orbital ellipse within its orbital plane, is explained by gravitation being mediated by the curvature of spacetime. Einstein showed that general relativity agrees closely with the observed amount of perihelion shift. This was a powerful factor motivating the adoption of general relativity.

Also, why should we not 'future proof' the article against possible revolutions in science? Science is not future-proof, why pretend that it is? PAR (talk) 02:49, 29 May 2021 (UTC)

PAR (talk · contribs)

Doing that everywhere is too awkward. "As of May 2021, Paris is the capital of France". Sure, it might change. But (a) it's not likely to happen anytime soon and (b) it's guaranteed that the article will be adjusted if it changes. Wikipedia always reflects the current knowledge, it can't do more than that. 90% of Mercury's perihelion precession can be explained in Newtonian physics as influence of other planets, by the way. --mfb (talk) 06:45, 29 May 2021 (UTC)

You're right, I should have said "anomalous precession" rather than precession. The Wikipedia article correctly refers to the "remaining precession". But I am not advocating that every article be overhauled, that's crazy. All I am saying is that when we are talking about a theory's place in the scientific body of knowledge, or the comparison of two apparently conflicting theories, only then do we have to be careful. And it need not be awkward. The statement "the most accurate description of gravity..." is speaking to the theory's place in the body of science, and there we have to be careful. In an article on Newton's theory alone, no changes need be made. On an article on general relativity, no changes need be made. But in an article on gravity where we are comparing the two, or addressing their validity, then I'm hoping for some accuracy.

If the people of France vote to change the capital, it changes, but if they vote to repeal the law of gravity, they are out of luck. "Paris is the capital of France" is outside the realm of science, and I'm only talking about science.

@@PAR:: Your above restatement has exactly the same problem. Also agree with MrOllie that "essentially equivalent to Newton's law for nonrelativistic situations" isn't great. --Chetvorno^TALK 18:55, 28 May 2021 (UTC)

To say "for most applications, gravity is well approximated by Newton's law" is too parochial. For a communications engineer working with satellites and GPS systems for your IPhone, none of the applications use Newtonian gravity. For an engineer involved with high precision atomic clocks, none of the applications use Newtonian gravity. Newtonian gravity is used for calculating space probe trajectories, but without those atomic clocks, the calculations would be useless. For most everyday applications, we use an approximation to Newtonian gravity developed by Galileo - We say the acceleration due to gravity is constant, so the weight of an object is simply proportional to its mass, which works since our distance from the center of the earth is essentially constant. "general relativity is essentially equivalent to Newton's law for non-relativistic situations" has none of these problems. PAR (talk) 02:49, 29 May 2021 (UTC)

Very few people work with satellites or the details of GPS. For almost everyone Newton's law is an excellent approximation for everything they do, the statement you quoted is correct and easier to understand than your proposal. Constant acceleration is another good approximation in many cases, but not as many as Newton's law. --mfb (talk) 06:45, 29 May 2021 (UTC)

When you go into a grocery store and read "net weight 2 pounds" or "net weight 12 ounces", do you think "well that's fine for people at sea level, but what about me, sitting here at 1000 feet above sea level?" When some guy brags about pressing 300 pounds in Denver, does anyone remind him of the fact that it was actually slightly less, since Denver is a mile high? 99 percent of everyday people make the constant acceleration assumption 99 percent of the time whenever they draw no distinction between weight and mass. Does anyone other than people doing orbital mechanics at non-cosmological distances use Newton's full law? I am a scientist and I have never used it except to pass a college exam. I deal with chemistry and thermodynamics in which gravity is a negligible factor. PAR (talk) 16:58, 29 May 2021 (UTC)

Maybe I missed it, but @PAR, can you explain what's inadequate or inferior about the current wording and why it should be changed? -Jordgette [talk] 14:14, 29 May 2021 (UTC)

@Jordgette - At the beginning of the second paragraph it says: "Gravity is most accurately described by the general theory of relativity". I inserted "At present, gravity is....". It's not a huge deal, but the arguments against it are problematic to me. The reason I changed it was because it sounded like the final word on gravity has finally been found, and science never goes that far.

Also, I have a problem with "However, for most applications, gravity is well approximated by Newton's law of universal gravitation". I think this is parochial - In someone's own world, it may be true, In someone else's it wont be, and 99 percent of the use of the law of gravity is based on Galileo's assumption that gravity produces a constant acceleration, not Newton's law. I want to replace it with "general relativity is essentially equivalent to Newton's law for non-relativistic situations" which I think is more informative and not parochial. Going back and forth, there is what I think is a better version for the entire paragraph:

Newton's law of universal gravitation was the first scientific description of gravity, which described gravity as a force causing any two bodies to be attracted toward each other, with magnitude proportional to the product of their masses and inversely proportional to the square of the distance between them. Newton's law of gravitation has been superseded by the general theory of relativity (proposed by Albert Einstein in 1915), which is a more accurate and general theory of gravitation, and is essentially equivalent to Newton's law for non-relativistic situations. General relativity describes gravity not as a force, but as a consequence of masses moving along geodesic lines in a curved spacetime caused by the uneven distribution of mass. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon.

PAR (talk) 16:58, 29 May 2021 (UTC)

But gravity is most accurately described by GR, and gravity is well approximated by Newton's law for most applications. That language is plain, effective, and direct. Why weaken it and make it more wordy? "science never goes that far" — exactly. For that reason, "at present" is unnecessary and potentially confusing. It looks like you're a one-person minority opinion here. -Jordgette [talk] 18:41, 29 May 2021 (UTC)

Oh, I know I'm a one person minority, and I have no intention of editing the article unless that changes. But that doesn't mean I'm wrong. Maybe I am, and I will listen to arguments, but I won't listen to arguments that simply say I'm wrong.

What is the meaning of "gravity is most accurately described by GR"? To me that implies that it cannot be replaced by a more accurate theory, which is confusing at best and wrong at worst. I understand, the argument is that the statement IMPLIES "gravity is most accurately described by GR at the present time and may or may not be superseded in the future by something better", but that to say that is "awkward". I think the above paragraph is accurate, not awkward, and simply avoids making that controversial and confusing statement.

What is the meaning of "for most applications, gravity is well approximated by Newton's law of universal gravitation"? If we count up the number of times everyday people make use of the theory of gravitation, they overwhelmingly do not use Newton's law, they use the constant acceleration assumption, in which weight and mass are used interchangeably. How do you justify saying "for most applications, gravity is well approximated by Newton's law of universal gravitation"? Why not say the more informative and less controversial "GR gives practically the same results as Newton's law in non-relativistic situations"? That is a statement that won't be objected to by anyone, no matter what little technical world they live in.

I've tried to explain that this does not imply that every scientific article needs to be overhauled. Only when you are worrying about where a scientific theory fits into the big picture (like GR in the above statement), or comparing how two theories fit in the big picture (like Newton vs. GR), do you need to be concerned. If you say "its implied, end of story", then ok, end of thread. If you define "most applications" as "most applications except those of everyday people". then ok, end of thread. I'm not responding here with any expectation of changing the article, I'm learning how people view science and maybe altering my own, learning something, and maybe having them re-examine theirs. For example, I never considered the idea that every article would have to be overhauled, and since that's obviously crazy, I had to think about what I really meant to say, and in so doing refined my own understanding of what science is all about. "You are just wrong" is useless to me, I have way better things to do. PAR (talk) 22:03, 29 May 2021 (UTC)

PAR, I don't think our readers should need to know what a 'relativistic situation' is to understand the article lead. Simple language should be preferred whenever practical. MrOllie (talk) 22:24, 29 May 2021 (UTC)

Yes. Is there a way of saying it without using the term "relativistic situation"? Like "... which is a more accurate and general theory of gravitation. For most applications involving the calculation of the orbits of planets and other objects, the two theories give practically the same results, with some notable exceptions" PAR (talk) 15:13, 1 June 2021 (UTC)

Adjustment for centrifugal force seems suspect

I was annoyed that the article adjusted the force of gravity for centrifugal effects, since I'm interested in the force of gravity, not net forces of other kinds. So I tried calculating the actual force of gravity at the equator based on the force of gravity at the poles (where centrifugal effects are near zero) and adjusting for the distance from the core at the equator, per the square-inverse law.

The calculated purely-gravitational force at the equator came to almost exactly the force cited in the article for net gravitational and centrifugal effects. It was close enough that the difference falls below the threshold of the significant figures used.

Showing my math: http://ciar.org/h/82d6ee.txt

Is it possible that someone was just confused, and decided that since the widening of the earth at the equator is due to centrifugal effects, the force of gravity was also less due to centrifugal effects, and simply misrepresented the effect of the difference in distance?

TTK (talk) 18:32, 29 June 2021 (UTC)