Talk:Gravity

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Opening sentence needs reconsidering

Gravity or gravitation is a natural phenomenon by which all things with energy are brought toward (or gravitate toward) one another, including stars, planets, galaxies and even light and sub-atomic particles.

While the mention of "with energy" may be technically correct due to mass/energy equivalence, it is much too confusing for the ordinary reader to drop this into the opening sentence without any further (at this point) explanation. 31.49.180.255 (talk) 01:57, 26 September 2016 (UTC)

I absolutely agree. This is a good example of a common problem on WP technical articles; editors generalizing the first sentence until it is incomprehensible. There are many better ways to state this point in the intro, which a good writer would use; for example:

"Gravity or gravitation is a natural phenomenon by which all things with mass are brought toward (or gravitate toward) one another, including stars, planets, and galaxies. Since energy and mass are equivalent, all forms of energy such as light are also included."

Another dweeby example of bad writing in this introduction is:

"Gravity is responsible for many of the structures in the Universe, by creating spheres of hydrogen — where hydrogen fuses under pressure to form stars — and grouping them into galaxies"

Gravity doesn't create spheres of hydrogen out of nothing, does it? Read the sentence as if you are a non-technically-educated reader, and that's what it seems to mean. Instead, why can't we just say:

"The gravitational attraction of the original gaseous matter in the universe caused it to collapse together, forming stars — and the stars to group together into galaxies — so gravity is responsible for the large scale structures in the Universe."

This lead paragraph sounds like it was written by a teenage Sheldon Cooper, not a competent science writer. Seriously, come on. --Chetvorno^TALK 03:37, 26 September 2016 (UTC)

I don't agree with the first one. Light has no mass, so suggesting that it can be "included" in "all things with mass", would be a bad idea. It can be included in "all things that gravitate or that cause and are under the influence of gravitation", but not in all things with mass. In order to avoid circularity we can't of course mention gravity or gravitation. Perhaps there is another way to state the point correctly, but I think that the the current wording is very okay. It invites the ordinary reader who might expect mass here, to be somewhat puzzled and by all means go on reading. - DVdm (talk) 08:44, 26 September 2016 (UTC)

Your proposed version would be fine with me:

"Gravity or gravitation is a natural phenomenon by which all things with mass are brought toward (or gravitate toward) one another, including stars, planets, and galaxies. Since energy and mass are equivalent, all forms of energy such as light are also under the influence of gravitation."

I don't object to a sentence that gravitation acts on "all things with energy"; I just don't think it should be the lead sentence. I just think the intro shouldn't be 'puzzling' the readers; this subject is already puzzling enough for nontechnical people. "It is particularly important for the lead section to be understandable to a broad readership." (WP:EXPLAINLEAD) "Do not hint at startling facts without describing them." (MOS:LEAD) "The average reader should not be shocked, surprised, or overwhelmingly confused by your article." (WP:ASTONISH) "[The lead] should not "tease" the reader by hinting at but not explaining important facts that will appear later in the article." (MOS:INTRO) Many general readers with no scientific education come to this page just wanting the simplest, most understandable explanation of gravity. I think the current confusing lead sentence will just discourage them. --Chetvorno^TALK 21:17, 26 September 2016 (UTC)

The amended phrase "all forms of energy such as light are also under the influence of gravitation" is almost fine. I'd add something to make it complete:

"Gravity or gravitation is a natural phenomenon by which all things with mass are brought toward (or gravitate toward) one another, including stars, planets, and galaxies. Since energy and mass are equivalent, all forms of energy such as light also cause gravitation and are under the influence of it."

Do you see another acceptable way to say that these forms are also sources of gravitation? - DVdm (talk) 21:27, 26 September 2016 (UTC)

FWIW - Perhaps the following wording may be better? =>

• Suggestion-1: "Gravity, or gravitation, is a natural force with which all things with mass are brought toward one another (including planets, stars and galaxies). Since energy and mass are equivalent, all forms of energy (including light) cause, and are influenced by, gravitation."
  

MORE Simply? =>

• Suggestion-2: "Gravity, or gravitation, is a natural force with which all things with mass (including planets, stars and galaxies) and energy (including light) are physically attracted to one another."
  

COMPARE? =>

• Wiktionary: "Gravity, or gravitation, universal force exercised by two bodies onto each other."
  

• Encyclopedia Britannica: "Gravity, also called gravitation, in mechanics, the universal force of attraction acting between all matter. It is by far the weakest known force in nature and thus plays no role in determining the internal properties of everyday matter. On the other hand, through its long reach and universal action, it controls the trajectories of bodies in the solar system and elsewhere in the universe and the structures and evolution of stars, galaxies, and the whole cosmos..."
  

IN Any case - Enjoy! :) Drbogdan (talk) 21:52, 26 September 2016 (UTC)

@Drbogdan I totally agree with Suggestion-2. "all things with mass" because everything with energy is not effected by gravity, photons for example. Whereas all things with mass are physically attracted to each other. However, light does not have its "own gravitational mass". - Worldandhistory (talk) 15:09, 28 September 2016 (UTC)

@Worldandhistory: Thank you for your comments - seems, after a casual Google Search, there may be many WP:RS that suggest photons (or light) are influenced by gravity in fact - one worthy (imo) explanation may be from the Physics Department at the University of Illinois (also see "Photon#Contributions to the mass of a system") - in any case - Thanks again for your comments - and - Enjoy! :) Drbogdan (talk) 15:29, 28 September 2016 (UTC)

@Drbogdan, if you are convinced for your proposed claim that "photons (or light) are influenced by gravity" and happen to have reliable sources to back your claim, you may add the info then. :) Best - Worldandhistory (talk) 16:11, 28 September 2016 (UTC)

@Worldandhistory: Thanks for your comments - perhaps the following quote (or at least WP:RS) may be considered in some form?

Copied from "Photon#Contributions to the mass of a system":

Since photons contribute to the stress–energy tensor, they exert a gravitational attraction on other objects, according to the theory of general relativity. Conversely, photons are themselves affected by gravity; their normally straight trajectories may be bent by warped spacetime, as in gravitational lensing, and their frequencies may be lowered by moving to a higher gravitational potential, as in the Pound–Rebka experiment. However, these effects are not specific to photons; exactly the same effects would be predicted for classical electromagnetic waves.

References

In any case - Enjoy! :) Drbogdan (talk) 16:30, 28 September 2016 (UTC)

I disagree with the suggested changes to the wording of the first sentence. I think the sentence as written accurately and succinctly establishes the more universally accepted notion that gravity is associated with energy rather than the traditionally referred to notion of mass. Even to the average reader, this article establishes correctly, right from the get-go, that to understand gravity in the present age, gravity is not a force, but rather a phenomenon, and that Newton's laws were approximations superseded by the more universal Theory of Relativity. SquashEngineer (talk) 15:42, 28 September 2016 (UTC)

Agree. Let's keep that opening sentence. It perfectly reflects the body of the article. And it is correct. - DVdm (talk) 19:51, 28 September 2016 (UTC)

@SquashEngineer Hi, can you please share a reliable source that backs your claim; "gravity is not a force, but rather a phenomenon, and that Newton's laws were approximations superseded by the more universal Theory of Relativity"? If you do please do share here for knowledge. I still think the first sentences are confusing and ambiguous. But again, I can be wrong. Best - Worldandhistory (talk) 16:11, 28 September 2016 (UTC)

Please indent the messages as outlined in wp:THREAD and wp:INDENT. Thanks.

The opening sentence reflects what is in the article and there is nothing confusing and ambiguous about it, just like there is nothing confusing and ambiguous about the opening sentence of Bing Bang, on the talk page of which you more less wrote the same as you did here. If, after having read the article, you find that something remains confusing and ambiguous, then you should probably go to the wp:Reference desk and ask topical questions there. An article talk page is not for requesting sources to support the first sentence—see WP:LEADCITE. You will find sources in the body of the article. - DVdm (talk) 19:51, 28 September 2016 (UTC)

@DVdm: I agree with you that the opening sentence is fully supported, and Drbogdan should read the sources if he has questions. But it is clear from 31.49.180.255's and Drbogdan's comments that the concept of energy gravitating is unfamiliar to many (undoubtedly most) readers and I think it needs to be explained or stated explicitly, not "sprung" on them without explanation in the lead sentence. I think your suggested wording in your 21:27, 26 September 2016 post above would be great - better than mine. I think Drbogdan's Suggestion-1 wording above would be fine, and I could live with his Suggestion-2. But not mentioning mass (or some equivalent word like "bodies" or "particles") in the lead sentence defining gravity is going to be really confusing to many. I've looked at a bunch of textbooks [1] and I don't see any that define gravity as we do. --Chetvorno^TALK 22:27, 28 September 2016 (UTC)

@Chetvorno and DVdm: Thank you for your comments - to clarify - besides my own Suggestion-1 and Suggestion-2 versions of the opening lede sentence posted earlier above, the current opening lede sentence has also been *entirely* ok with me - nonetheless, I agree with the reasoning presented by User:Chetvorno - that my Suggestion-1 and/or Suggestion-2 may be preferred - and, perhaps, more reader-friendly (and accessible?) to the average reader - after all => "Readability of Wikipedia Articles" (BEST? => Score of 60/"9th grade/14yo" level) (also see my related post) - in any case - hope this helps in some way - Thanks again for your comments - and - Enjoy! :) Drbogdan (talk) 23:10, 28 September 2016 (UTC)

References

@All: ok, for now I have made the change as suggested 21:2, 26 September 2016, as indicated above by Chetvorno. Cheers. - DVdm (talk) 06:31, 29 September 2016 (UTC)

@Chetvorno, DVdm, SquashEngineer, and Worldandhistory: et al. => QUESTION: Should "Gravity", in the current opening sentence of the lede, be referred to as a "natural phenomenon" - or - as a "natural force" instead? - after all - "natural phenomenon" is wikilinked to "List of natural phenomena", which doesn't seem to currently list the term "gravity" at all (perhaps it should?) - also - the term "force" seems to be the preferred term (actually, "universal force") in "Wiktionary - Gravity", as well as the preferred term (actually, "universal force") in the "Encyclopedia Britannica - Gravity" - in any case - Enjoy! :) Drbogdan (talk) 12:19, 29 September 2016 (UTC)

Hm, I certainly wouldn't do that. After all, in general relativity, which is our best model of gravity, it is not a force at all. So it's probably better to be neutral here and leave all options open by just using the generic natural phenomenon, which is then explicitised to force and spacetime curvature later in the article, depending on the context.

But It would indeed be a good idea to include a wikilinked Gravity in that list—even if I'm not a fan of such list-articles. As far I'm concerned, go ahead with the list. - DVdm (talk) 13:49, 29 September 2016 (UTC)

 Done - @DVdm: Thank you for the comments - and suggestion to add "Gravity" in the "List of natural phenomena" article - no problem whatsoever - added "Gravity" under a newly created "Physical" subgroup - for starters at least - *entirely* ok with me to rm/rv/mv/ce the edit of course - iac - Enjoy! :) Drbogdan (talk) 14:16, 29 September 2016 (UTC)

Since it's already decided, sorry for delayed response. I agree with DVdm to be neutral here. However, according to me, it should be referred to as a "natural force", as it exists/is present with every object as can be seen here with an example of dice. The Earth's strong gravitational force simply doesn't allow two objects as small as dice to react to their gravitational forces, but if they are placed in non-gravitational environment, they will simply collide. Using the term phenomenon might not be a good idea, according to me, since there is not question or doubt about the existence of Gravity in all things. BR - Worldandhistory (talk) 17:59, 29 September 2016 (UTC)

@DVdm: the new lead looks fine to me. --Chetvorno^TALK 02:09, 3 October 2016 (UTC)

@Drbogdan: Since we're making a point of being correct and not calling gravity a force in the rest of the article, it probably shouldn't be called a force in the lead sentence. --Chetvorno^TALK

@Chetvorno: Thanks for your comment - yes - agreed - no problem whatsoever - Thanks again - and - Enjoy! :) Drbogdan (talk) 08:21, 3 October 2016 (UTC)

Bit late, but there really is no reason to say "everything with mass" as opposed to "everything with energy". It is simply misleading. Sir Cumference π 01:02, 5 January 2017 (UTC)

The 2nd sentence resolves any confusion. --Chetvorno^TALK 02:13, 5 January 2017 (UTC)

Isn't it worth generalizing a bit more? In GR, mass isn't the only source of gravity. Energy, momentum, pressure, etc. are relevant. Perhaps we could say something more ambiguous, like "Gravity or gravitation is a natural phenomenon by which all forms of matter are brought toward (or gravitate toward) one another, including stars, planets, galaxies and even light and sub-atomic particles." Sir Cumference π 19:56, 5 January 2017 (UTC)

The 2nd sentence explains that energy is included, so I feel there is no need for the additions you propose. Other problems I have with the proposed lead:

• The proposed sentence is logically inconsistent, since light is not a form of "matter".
• It is also misleading since by mentioning "sub-atomic particles" explicitly it implies that gravity is a significant force on them. While of course as the constituent of all matter subatomic particles are acted on by gravity, the force of gravity on a single particle is utterly negligible. We don't want to give introductory readers the impression that gravity is a significant player in atomic physics.

--Chetvorno^TALK 20:51, 5 January 2017 (UTC)

After reviewing this (exhaustive) discussion of the lead sentence(s), I would like to suggest the following change from the current "Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward (or gravitate toward) one another, including objects ranging from electrons and atoms, to planets, stars, and galaxies. Since energy and mass are equivalent, all forms of energy (including photons and light) cause gravitation and are under the influence of it." to "Gravity, or gravitation, is a natural phenomenon by which all things with mass or energy--including planets, stars, galaxies, and even light--are brought toward (or gravitate toward) one another." I make this suggestion in the interest of simplification and brevity.
-Catwilsonaz (talk) 20:06, 21 June 2018 (UTC)

Nature Timeline graphic

The graphic titled {{Nature timeline}} seems to provide an incorrect link to the wiki article that refers to the History of Life timeline: https://en.wikipedia.org/wiki/Timeline_of_natural_history

rather than the more encompassing Formation of the Universe timeline: https://en.wikipedia.org/wiki/Timeline_of_the_formation_of_the_Universe

which I think is more representative of the image provided.

The History of Life timeline is simply a subset of the Formation of the Universe timeline. I was confused by the link when clearly the two images differ in scale and overall content between the linking articles. The Nature Timeline graphic and link are utilized within multiple articles. SquashEngineer (talk) 15:42, 28 September 2016 (UTC)

 Done - @SquashEngineer: Thank you for your comments - and suggestion to adjust the title-link of the {{Nature timeline}} template from "Timeline of natural history" to "Timeline of the formation of the Universe" instead - yes - agreed - template title-link has now been updated - Thanks again for your comments and suggestion - and - Enjoy! :) Drbogdan (talk) 16:03, 28 September 2016 (UTC)

New Paradigm shift for Gravity?

FWIW - Of possible interest - re a new way of understanding "Gravity"? - worthy of mention in the main "Gravity" article? - in any case - Enjoy! :) Drbogdan (talk) 14:33, 19 November 2016 (UTC)

References

The first link is identical to the second article? A cosmologist wrote another arXiv entry on gravity. I don't see the importance so far. --mfb (talk) 19:55, 19 November 2016 (UTC)

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Semi-protected edit request on 18 July 2017

2601:588:0:8A3E:6C68:17B2:C8FD:556D (talk) 19:48, 18 July 2017 (UTC)

Kids Version of The Gravitational Force'. Its a very simple concept its what keeps us from floating into space. Its what keeps all objects from floating. It also brings objects closer together. Its been around longer than this earth has been. Its an amazing thing. You and I would not be here without it. We just float our way to the atmosphere. Its just that important.

Not done: it's not clear what changes you want to be made. Please mention the specific changes in a "change X to Y" format. Morphdog^{what did I do now?} 20:01, 18 July 2017 (UTC)

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gravity "OR" gravitation ...

so what does "gravity center" [rigid body] and "special gravity" [i.e. mass density] mean (if it's not weight)? gravity means being grave (heavy). if we draw force vector between, it starts from weighted body (i.e. gravity) and ends to gravitator (here, earth). gravitation [: making heavy] acts on gravities, while electra and magnet make phenomena by itself: magnet makes magnetism, electra does electricity, but gravitation is "seen on" gravities. in comparison, gravitation, magnetization and electrification are in the same row.
Tabascofernandez (talk) 00:27, 24 September 2017 (UTC)

There is no "gravity center" in the article. Do you mean center of mass? --mfb (talk) 02:03, 24 September 2017 (UTC)

formula

what if we write it as k_G·m·m₀ /r² where k_G = 1/ 4πγ₀; in harmony with k_E·q·q₀ /r² {k_E = 1/ 4πε₀} and k_M·φ·φ₀ /r² {k_Μ = 1/ 4πμ₀}. if that be, c² = μ₀ε₀; so what does γ₀ do? [s² = γ₀ζ₀; k_Z = 1/ 4πζ₀; F = k_Z·β·β₀ /r² ] (Z-field I guess it's about hydrodynamics: a moving mass object (single, or in groups: air, water ..). {compare moving charge: magnetism}. also newton law: F_Z = mvK, K = β/A (compare: F_M = qvB, B = φ/A, or F_E = φvD, D = q/A or finally: F_G = βvJ, J = m/A)
Tabascofernandez (talk) 01:26, 24 September 2017 (UTC)

The first is just rewriting constants, and everything that follows doesn't look useful at all. This discussion page is for improvements of the article, not for the discussion of personal views on the topic. --mfb (talk) 02:03, 24 September 2017 (UTC)

Representing gravity in 3D

Hi wikipedia, I have been reading lots of comments elsewhere about people not understanding the standard "trampoline" representation showing how mass creates a gravity well, it makes many think space is flat (trampoline like). Would it not be better showing a 3D representation as well or instead of? ---- — Preceding unsigned comment added by Rod Fathers (talk • contribs) 14:01, 18 October 2017 (UTC)

The trampoline visualizes two space dimensions with a 3-dimensional picture. To visualize three space dimensions we would need a 4-dimensional picture. That is not going to help people. --mfb (talk) 08:47, 19 October 2017 (UTC)

I meant something like this video clip from utube https://www.youtube.com/watch?v=hH69B0Oc2Og Rod Fathers (talk) 23:50, 30 October 2017 (UTC)

I'm not sure if that is helpful, it can be very misleading. --mfb (talk) 08:21, 31 October 2017 (UTC)

Also let's not forget that gravity is modelled/described/caused by spacetime curvature. The animations and figures only show the spatial part of the curvature. - DVdm (talk) 10:14, 31 October 2017 (UTC)

Leonard Susskind is very generic sometimes

Motion is information. The black hole limits the motion of particles, so we have jets which dissipate that relative to it's surroundings information. Gravitational systems, are constituted of objects which slowly have their particles complexity degrading. A gravitational system, forces it's components to lose information. That means that all atoms in a gravitational group, tend to have slightly closer spin values, and slightly closer time-flow pace (relative timing among particles). The information isn't lost. It's simply transformed into motion. A gravitational system is very hard to describe, because it has many components, but if we await, we then can describe with fewer pages the characteristics of the particles'except from their relative speed. Dark energy is a result of quantum fluctuations in the void. Dark energy is a cause of differentiation, thus acts in bigger orders of magnitude, as antigravity. Dark matter, is the second order gravity, among the gravitational orbits/paths and not directly the gravity of objects. Even potential paths exhibit inertia. Even particles (which are most of the time fields and not particles) are inertial flows of potentiality. The Universal void exhibits more unbiased randomness at the Planckian level than matter, but there is no void in the Universe. The Universal void is a phenomenon within our Universal topoalgebraic algorithm, thus it's not a void. — Preceding unsigned comment added by 2A02:2149:8490:3400:608A:BDA2:6DF7:A815 (talk) 11:07, 2 February 2018 (UTC)

This Talk page is not the place to present your theories of gravity; it is only for discussing the article itself, see WP:Talk page guidelines, WP:NOTFORUM --Chetvorno^TALK 13:35, 2 February 2018 (UTC)

Anomalies and discrepancies

Extra energetic photons: Photons travelling through galaxy clusters should gain energy and then lose it again on the way out. The accelerating expansion of the Universe should stop the photons returning all the energy, but even taking this into account photons from the cosmic microwave background radiation gain twice as much energy as expected. This may indicate that gravity falls off faster than inverse-squared at certain distance scales.

"Travelling" really? please use spell check - traveling.

Brett TaylorRonston121 (talk) 13:57, 23 February 2018 (UTC)

Please note that on article talk pages we must discuss the article, not the subject—see wp:Talk page guidelines.

Also note that both "traveling" and "travelling" are perfect English—see [2] and [3]. And of course wp:ENGVAR and wp:RETAIN. Cheers. - DVdm (talk) 14:49, 23 February 2018 (UTC)

Known, and studied: Sachs-Wolfe effect. --mfb (talk) 00:52, 24 February 2018 (UTC)