Talk:Gravity/Archive 6

This is an archive of past discussions about Gravity. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Archive 1

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Archive 4

Where is the formula?

I visited this page specifically to remind myself of the formula for the gravitational attraction of two bodies. To my mind, that's a fundamental formula in any discussion about gravity. —Preceding unsigned comment added by 91.153.156.36 (talk) 14:53, 7 November 2007 (UTC)

I agree, I didn't find any reference to the page gravitational_constant anywhere in this article, even though the earth's gravitational constant is mentionted without a second thought. --KWifler —Preceding unsigned comment added by 24.22.176.33 (talk) 07:19, 30 May 2008 (UTC)

Gravity vs Centripetal Force

My friend says that Gravity is only an unproven theory and that Centripetal Force is what keeps everything on the Earth. LOL! --Can Not 01:19, 26 September 2007 (UTC)

Article Size = 47 kilobytes

Article Length = 16 pages (printed). There seems to be a lot of confusion in this article with regards to size / merge / split ideals. A group of us had a similar problem with thermodynamics article last year; it was similarly about 16 pages in length. Our solution was to write mini-articles for each topic conjoined with “see main” links attached. By doing this, over several months, we reduced the thermodynamics article to 7 pages (printed) and it is now listed in “good article” standing. I would suggest following this route with the gravity article. There is a documented principle (I’ve read somewhere?) which states that online-reading tension spans are limited; and that when an article is too lengthy the reader will typically give up. Yet, when an article is subdivided, with split-off topics, the reader’s efficiency will improve by allowing focused attention to desired subtopic. Please refer to the thermodynamics article as a model. Just a suggestion: --Sadi Carnot 16:25, 27 February 2006 (UTC)

The article is now 47 kilobytes. The maximum is 32 (see: article size). I don't know who keeps putting the merge requests up, but this article needs to be chopped up. Rules are Rules. 32 kilobytes is the maximum. If I end up doing it, it's going to be sloppy. I would hope someone who has worked on this article would do it soon. I would suggest breaking this up into at least five pages; that way some of us who have interest in certain areas can contribute here or there as we please.--Sadi Carnot 04:45, 9 March 2006 (UTC)

I agree. As a casual reader of science topics and Wikipedia editor, split this baby up. As indicated, splitting off the Newtonian/math section seems appropriate and fairly simple. I'd also suggest keeping quantum mechanics and quantum particle physics out of this altogether, with only brief linking statements about the deeper implications of gravity and attempts at a unified theory. Go ahead and do it Sadi, be bold. DavidH 07:22, 10 March 2006 (UTC)

How about using a /Gravity_page to partition out this idea? --Ancheta Wis 10:41, 10 March 2006 (UTC)

0 Intro paragraphs

1 Overview of the history of gravitational theory

2 The Earth's gravity

2.1 Comparative gravities of the Earth, Sun, Moon and planets

3 Mathematical equations for a falling body

3.1 Gravitational potential

3.2 Acceleration relative to the rotating Earth

4 Gravity and astronomy

4.1 Self-gravitating system

5 Practical uses of gravity

6 Newton's law of universal gravitation

6.1 Acceleration due to gravity

6.2 Bodies with spatial extent

6.3 Vector form

6.4 Gravitational field

7 Problems with Newton's theory

7.1 Theoretical concerns

7.2 Disagreement with observation

7.3 Newton's reservations

8 Einstein's theory of gravitation

8.1 Experimental tests

9 Comparison with electromagnetic force

10 Gravity and quantum mechanics

11 Alternative theories

11.1 Recent alternative theories

11.2 Historical alternative theories

12 Notes

13 See also

14 References

15 External links

Thanks for the support and ideas, keep them coming (however we can't have 30 headers). Last week I broke up the (over-the-limit) love article into four pages, and that seemed to go fairly well:

If I break up this one, I will likely outline it similar to that of Britannica’s (CD-ROM) article on gravitation. They do a redirect from gravity to gravitation; this is the way it is done in most physics textbooks as well. Britannica has over 200 year’s experience on this matter. Similarly, from the force article, as we all know:

Types of force

There are four known fundamental forces in nature.

Nuclear forces acting between subatomic particles
Electromagnetic forces between electric charges
Weak forces arising from radioactive decay
Gravitational forces between masses

Hence, when people look up “gravitation”, “gravity, “force of gravitation”, “gravitational force”, etc., for the sake of organization (without getting into some esoteric debate), we would redirect all to one page; then on this main page, i.e. Gravitation, being short in length, give the following overview of gravitation (with branch-off points throughout):

introduction
History

short paragraph

Newton’s Law

short paragraph

Relativity

short paragraph

Recent theories

short paragraph

See also
References
External links

This is rough outline (maybe with one more section?). We would then put the rest in the See also section, thus keeping the main page very simple. In this manner, it will have room to grow. If we have any grave objections we can always revert. Again, if someone else wants to do the break up then by all means do so. Are we all relatively O.K with this?--Sadi Carnot 17:50, 11 March 2006 (UTC)

Hmm...

Wouldn't it be useful to separate Gravity from Gravity theory? The former would include the documented evidence, and the latter would include the speculative thought. This is how many similar topics are discussed. (See: theory#List of famous theories). KSchutte 19:14, 12 March 2006 (UTC)

That would be nice in principle; however, what happens is that people stumble upon the lesser of the two articles, assume it to be an untapped editing prospect, then start adding duplicate content, e.g. there were two separate history sections growing on the former separate “gravity” and “gravitation” articles. Read the arguments on the archive pages as well. --Sadi Carnot 15:44, 14 March 2006 (UTC)

Beginning merge & break-up

Completing merge and break-up of "joint" articles per Talk:Gravity discussion, gravitation talk page archives, and gravity talk page archives.--Sadi Carnot 05:56, 14 March 2006 (UTC)

Gravity could be completely wrong nobody truly knows what keeps us on the earth gravity is just one version of it Cahan123 (talk) 08:36, 22 May 2008 (UTC)

Done with split-up

Gravity is now a redirect to Gravitation, in accordance with the above discussions (and per archives). The main article has now been reduced from 18 pages to 5. In doing this, seven new pages have been created as branched off from the main article, and the total set of eight pages (verses one) is now very workable. I apologize if the breakup was emotional for anyone. Almost nothing was deleted, most was simply redistributed and reorganized.--Sadi Carnot 09:59, 14 March 2006 (UTC)

Congratulations and thank you. --Ancheta Wis 12:07, 14 March 2006 (UTC)

Very well done, although I was taken by surprise by this. (I have not been active on the gravity page recently, but have kept an active watch here to maintain the integrity of this page.) It is nice to see that my firm stand against redirecting this topic to "gravity" has finally paid off. This is very much the kind of thing that I hope to have this page become. --EMS | Talk 16:39, 14 March 2006 (UTC)

Einstein's nationality

The current text is "American (German-born) physicist Albert Einstein". My object is that Einstein was a German physicist at time general relativity was created, and IMO should be listed as such. That he later emigrated to America is immaterial to his status at the time general relativity was developed. The other option is not to deal with the nationalities of well-known people like Einstein and Newton at all. (Note that this issue also related to the page Einstein's theory of gravitation. --EMS | Talk 16:52, 14 March 2006 (UTC)

But I thought he renounced his German citizenship. OK even if he was granted German citizenship when he was professor in Germany, he lost that when he lost his job. What about simply omitting the attribution? -- or German / Swiss / American ? --Ancheta Wis 17:14, 14 March 2006 (UTC)

I agree with you both; however, as a general of thumb (in science writing) most attach a name to a nationality + type of scientist; whereby we assume, no matter how famous, that the reader has no prior knowledge of the person. In this manner, the learning process is improved: people will attach an unknown name, such as “Albert Einstein” with an occupation, as “physicist”, to a national origin, as “German-born American”. This, by the way, is how Merriam-Webster describes Einstein in their one paragraph summary.--Sadi Carnot 17:23, 14 March 2006 (UTC)

In 1915, Einstein's renouncing his German citizenship was still ~20 years in the future. The issue is one of do we describe Einstein as he was when he created the theory, or as he was at his death? A case can be made for both, or for the alternative of not mentioning nationality at all in order to avoid this can of worms. At this point, my temptation is to leave it alone unless a consensus appears to change it, partially out of respect to Sadi's argument above and partially out of respect for the amount of thought and work that Sadi is putting into these articles. --EMS | Talk 18:12, 14 March 2006 (UTC)

EMS, Actually he first renounced it in 1896. But SC, I concur with your work. --Ancheta Wis 18:26, 14 March 2006 (UTC)

LOL! After looking at the link, it is now my conclusion that the correct text is "Swiss-American (born German) ...". --EMS | Talk 20:54, 14 March 2006 (UTC)

Sounds accurate, how about: "the German-born, Swiss-American physicist Albert Einstein "? This seems cogent. Feel free to change it.--Sadi Carnot 21:23, 14 March 2006 (UTC)

Sheesh, I can't believe that no-one suggested the simplest and wisest solution: Albert Einstein rather than the born-in-Ulm-schooled-in-Berne-worked-in-Vienna-later-lived-in-Berlin-and-still-later-fled-to-Princeton-Swiss-German-American-and-by-his-own-account-devoutly-trans-national mostly-theoretical-but-sometimes-experimental physicist-and-philosopher-and-sometime-inventor-and-as-some-would-say-theologian-which-as-some-would-say-makes-him-an-applied-mathematician-and-engineer-but-certainly-not-a-monk Albert Einstein.---CH 07:55, 21 April 2006 (UTC)

Good lord. Just change it to "then-German scientist Albert Einstein" and be done with it. 209.214.230.142 20:54, 23 June 2006 (UTC)

Gravity and superconductors

Interesting news going around today (2006-03-25) about some tiny aparrent changes in gravity from rotating rings of semiconductors. http://xxx.lanl.gov/abs/gr-qc/0207123.pdf Waaay over my head! Needs a physicist to explain where this fits in. If it does. —Preceding unsigned comment added by 83.104.55.73 (talk • contribs) (demon.uk in merrie old England)

Thanks for the heads-up Anon, interesting article.--Sadi Carnot 01:50, 28 March 2006 (UTC)

Failed GA

The article failed to reach good article status because:

The applications section is poorly focused and the link to Lynton & Lynmouth Cliff does not work. There are obviously a number of applications of gravitation and the section would benefit from being rewritten.
- commented out the L&LC link. Ancheta Wis 01:28, 11 April 2006 (UTC)
The alternatives section does not properly highlight how widely accepted such theories are or are not.
The article could use a better sectioning. "Related" is not a good section heading for half the article's content.
Overall the article felt a little brief for such an important subject. Specifically it seemed to lack discussion on 20th and 21st century research/findings related to the subject beyond the brief synopsis it gave of Einstien's work (and the occassional references it made to open questions).

Please feel free to resubmit this article, once you feel these points have been addressed.

Cedars 10:52, 10 April 2006 (UTC)

Tesla/Puthoff crank-POV pushing edits

User:Sadi Carnot (?!) apparently added (by some mistake?) these descriptions:

Nikola Tesla challenged Albert Einstein's theory of relativity, announcing he was working on a Dynamic theory of gravity (which began between 1892 and 1894) and argued that a "field of force" was a better concept and focused on media with electromagnetic energy that fill all of space.
Induced gravity: In 1967 Andrei Sakharov proposed something similar, if not essentially identical. His theory has been adopted and promoted by Messrs. Haisch, Rueda and Puthoff who, among other things, explain that gravitational and inertial mass are identical and that high speed rotation can reduce (relative) mass. Combining these notions with those of Thomas Townsend Brown, it is relatively easy to conceive how field propulsion vehicles such as "flying saucers" could be engineered given a suitable source of power.

These claims are profoundly inaccurate. Tesla's announcement provides insufficient details to compare it with any published theory. Sakharov's proposal does have some coherent motivation and is still taken seriously despite (according to the mainstream view) lack of progress along these lines; Tesla's murky ideas have been entirely forgotten. The work of Haisch, Rueda, and Puthoff is fringe physics at best. Finally, Thomas Townsend Brown can only be regarded as a crank.

I have eliminated these particular cranky-POV-pushing edits, but there may well be others in this article. May the reader beware.---CH 21:57, 13 April 2006 (UTC)

I noticed some other errors, e.g. in general relativity gravitational radiation (which under the rules of quantum mechanics must be composed of gravitons) is created only in situations where the curvature of spacetime is oscillating contains at least one error. This seems to have involved trying to redress the ill effects of some massive merger/redirection war, so the cranky stuff quoted above may have been written by someone else and pasted into this article by Sadi during a rather massive reconstruction, which is why I say above the editions may have been a mistake. Be this as it may, the fact that they went unnoticed from 13 March 2006 to 13 April 2006 must be troubling to those of us concerned to improve and maintain the reliability of WP as an encylopedia.---CH 22:34, 13 April 2006 (UTC)

Hillman, why don't you do some research before pointing fingers. Every single wikipedia edit is stored in easily-accessible memory. Thus, if you would have done your investigation properly, you would have found that User:Gbleem put these questionables into the pre-merger Gravity article on Nov 2, 2005, see: Edit. Myself, I spent one day only (March 14, 2006) doing a breakup of an over-bulging Gravity + Gravitation set of articles. I would hope, in the future, that you do not go around affixing my name to any other questionable contributions that were made years ago by other people. Thank-you.--Sadi Carnot 02:39, 19 April 2006 (UTC)

Sadi, thanks for clearing this up. But please assume good faith. I think it is clear from my comment above that I did do some research, in fact I probably tried harder than most editors would have done to figure out what had happened. I even tried to clearly explain that I suspected I had not uncovered the whole story. Frankly, instead of yelling at me, I think you should give me credit for finding the edit I cited and for figuring out that it seemed to have something to do with some kind of merger or name change. I even said that I realized that you might not have been the original author! All you needed to say here was, indeed, during a merger from Gravity, which was then a separate article, I pasted in material written by Gbleem; I now wish I had read that material more carefully.

The real problem is that in cases like this, where material written by user U is merged from article A into article B by user V, it can be quite difficult to figure out what happened even by a careful perusal of the history file of B, unless you somehow guess that the needed information might be contained in the history file of A! In this case, the history file of B didn't tell me what I needed to know, namely that material was being merged by V from A and that I should look in the history file of A to find that the original author of the inaccurate claim was U. Obviously, it would be very useful to have a who-wrote-this? tool which is smart enought to unravel this kind of thing even if (as sometimes happens) article A no longer exists or has been reduced to a redirect!

Anyway, thanks for your work in the merger. I do think this episode shows why anyone carrying out such a merger should try to fact check anything which appears suspicious, since any attempt to improve the WP is rather defeated if one perpetuates such a wild claim. But I do realize that this might not always be possible. I think this episode highlights some serious problems with current wikisoftware, which can all too easily lead to this kind of misunderstanding. I hope that some developer will see this and attempt to develop the kind of tool described in the previous paragraph.---CH 02:10, 21 April 2006 (UTC)

As an aside, Tesla also denounced Einstein's methods, stating that "Einstein is trying to replace science with mathematics." This is an apparent reference to the fact that his theories were considered largely unprovable at the time of their publication. 209.214.230.142 21:25, 23 June 2006 (UTC)

Tesla was right!

Gravity is not a pulling force, it is a PUSHING force, it is the VIRTUAL PARTICLES surrounding a planet, PUSHING down the objects. Matter is mostly space but some objects have farther between the smallest particles, and therefore they are lighter - there is less resistance, less particles to be hit by the virtual particles. Say a piece of lead for example, is very heavy simply because it is dense!. This "media with electromagnetic energy that fill all of space" EXISTS and is proven, it just happens to have the name VIRTUAL PARTICLES. For more in depth explanation gohere and press ctrl+F to bring up the search bar and paste "This is what gravity" into the search field and hit enter alternatively scroll down to 12/05/06 12:11 AM (Aaron Murakami). /Minoya 16:07, 14 December 2006 (UTC)

The history section is very strange

In the history section there are strange claims about ancient Indians being "the first to recognize gravity as a force of attraction". Namely, Brahmagupta said in 628 'it is in the nature of the earth to attract bodies'. Is it really something profound and ground-shattering? Does it really differ from what other ancient men thought long before him? In the article as it stands now we are supposed to believe that Newton was "building on these foundations". Are you serious? Did Newton know anything about Brahmagupta? I can see a lot of articles reflect now Hindutva propaganda in its crudest form. Am I the only person to resent it?

—Preceding unsigned comment added by 212.199.22.149 (talk • contribs)

No. Unfortunately this topic attracts all sorts of crank edits, and is difficult to maintain without engaging in prolonged controversy. Since last man standing wins, and reasonable people tire more quickly ... linas 13:02, 18 April 2006 (UTC)

I don't disagree with the often-cited WP goal of correcting a eurocentric bias which is evident in some (most?) of the English language literature, but of course we should discourage anyone from trying to replace eurocentric bias with indocentric bias! In this case, I think that simply deleting any claim to the effect that Indians were the first to recognize gravity as a force of attraction should suffice. Assuming the quotation credited to Brahmagupta is undisputed, I think that is notable, but readers should be allowed make up their own minds what if anything to infer from this quotation. ---CH 02:57, 21 April 2006 (UTC)

history of gravity and indian sages is innapropriate The basis for the scientific argument and its demonstration is being watered down far too much by ambigous claims of the sages in india etc. There are far too many religious and historical propostion that point to all sorts of basis for bona fide scientific work. This looks like an attempt to discredit Newton as the discoverer of gravity. Unless you can make scientific predictions from the writings of sages on critical scientific issues of today as evidence of their validity, i can bring all sorts of arguments of for example the origins of the theory of electrons on the african zulu caim of nature of 'small things' please avoid nationalistic, racial, religious pride from interfering with valid accepted truths on merit for discovery. --- —Preceding unsigned comment added by 196.200.29.165 (talk • contribs)

A bubble with a man in the center of Earth

Okay, one can tell this is coming from someone uneducated. I'm not sure if this is the right place for any inquiry such as this, but it doesn't seem as if putting it here would harm. Now, to the point: Let us say that there is a bubble of empty space near the center of earth, offset from the center by a certain bit. Now, let us put a man in there, or any object for that sake. How will gravity work on him? And what if we placed him in the actual center of earth, disregarding all realism. Some might see this as a paradox that means that at some point (assuming mass is evenly distributed throughout the globe), a particle at a certain depth will face less gravity. As such, it seems as if pressure on the particle will also be releaved, at least to an extent. —Preceding unsigned comment added by 213.161.189.107 (talk • contribs)

Your intuitions are correct. An object at the exact center of the Earth would feel no net gravitational force and would float at the center. The attraction to mass in any direction is exactly counterbalanced by matter in the opposite direction. If slighty offset from center, it would experience some force to move toward the center. It is true that inside the earth the gravitational force toward the center is less than it is at the surface, since now some the mass is on the other side of the body. A good place on Wikipedia to ask questions like this is at Wikipedia:Reference desk/Science . Hope that helps. --GangofOne 03:04, 21 April 2006 (UTC)

A mass in free space in the gravitational center of the earth would nevertheless be in an orbit and subject to orbital forces of the sun and the moon and the planets.WFPMWFPM (talk) 04:25, 24 June 2008 (UTC)

and because of how gravity warps spacetime he'd experience less time passing than us according to our frame of reference. --some anonymous guy 07:20 1 september 2006

Gravity and the solar system

Why doesn't the planets spiral inwards toward the sun or away from it? Why is it rotating perfectly around the sun? Wouldn't it spiral in or out because of the imperfect balance between the mass and speed of the planets versus the gravitational pull of the sun? —Preceding unsigned comment added by 71.141.178.226 (talk • contribs) (San Francisco, CA; this IP is registered to Southwestern Bell)

> There is a volume of solar wind to factor in also. ---User:Seb-Gibbs —Preceding comment was added at 16:19, 21 December 2007 (UTC)

This would be best directed toward Wikipedia:Reference desk/Science, where you will probably be told that in Newtonian theory, a central force law scaling like r^-2 admits stable closed orbits (they are ellipses), whereas other exponents would not. This is a standard topic in courses on theoretical physics, for example Landau and Lifschitz, Mechanics. ---CH 04:55, 21 April 2006 (UTC)

Einstein vandal?

Is "john davenport" in the Einstein section vandalism? I'm confused.

The header called "realted" should be named something more descriptive. "Related" means that the things under them are related? that the things under it are related to gravity? or the things above them? Its very vague. Fresheneesz 05:05, 10 May 2006 (UTC)

Changed to Specifics. Is this O.K.?--Sadi Carnot 13:04, 10 May 2006 (UTC)

Its better, i'm still fuzzy on what exactly that header means about what under it. Fresheneesz 07:49, 11 May 2006 (UTC)

Stable version now

Let's begin the discussion per the protocol. --Ancheta Wis 05:26, 11 July 2006 (UTC)

Let me get this straight: we want to make stable an article that didn't even get up to "Good" status? If we're stabilizing versions in order to avoid article degradation, why would we start with article that isn't particularly stellar? And even once it is good (or hey, even featured), why not simply link to the version that was "certified good/featured"? Why not keep the Wikiwiki version the main version and make the "certified" versions easily accessible from that page? JDoorj a m Talk 21:34, 11 July 2006 (UTC)

Forget I said it. The protocol does most of the things you're asking for. A good idea, just not one I'd run across before here. S B H arris 02:32, 12 July 2006 (UTC)

Just exactly how many pages have you slapped this on? It's a brand new proposal, that has all kinds of discussion still surroudning it. Please be calm abot it? -Splash - tk 20:15, 12 July 2006 (UTC)

aryabhata and gravitation

What is this theory of gravitation of Aryabhata based on heliocentric solar system? To the best of my knowledge Aryabhata did not formulate any theory of gravity worth its name.

--N shaji 01:21, 29 July 2006 (UTC)

Proposed changes to section "History of gravitational theory"

I propose changing the beginning of the section from "There have been numerous theories of gravitation since the time of the Greek philosopher Aristotle in the 4th century BC. He believed that there was no effect without a cause, ....." to the following: "Since the time of the Greek philosopher Aristotle in the 4th century BC, there have been numerous attempts to understand and explain what we now know as the force of gravitation. Although these attempted explanations can not be called "scientific" in the modern sense of the word, they are nonetheless precursors of a scientific attitude towards natural phenomena. Aristotle believed that there was no effect without a cause, &c &c &c....." Also, in accordance with the comment direrctly preceding this one, mention of Aryabhata will be excised. Please discuss, especially why these changes should NOT be made. Hi There 12:11, 3 August 2006 (UTC)

My only request is that that "... explain what we now know as the force of gravitation" shotenned to "... explain gravitation". Please realize that in the most modern gravitation theory, general relativity, gravitation is not due to a force. I also support the removal of the mention of Aryabhata. I have tolerated the mentioj of Aryabhata, but have never been 100% sure that it belonged here (nor 100% sure that it did not). It is nice to see a consensus finally apprearing on this issue. --EMS | Talk 00:57, 4 August 2006 (UTC)

Okay, I edited it and utilized your suggestion, although I made a few other slight changes from the text that I originally proposed; let me know what you think. Hi There 10:15, 4 August 2006 (UTC)

This looks good. Thanks much. --EMS | Talk 20:36, 5 August 2006 (UTC)

Electroweak?

The beginning of the article states, "Gravitation is one of the four fundamental interactions in nature, the other three being the electromagnetic force, the weak nuclear force, and the strong nuclear force." I read that the electromagnetic and weak forces were aspects of the same process. I suppose it's now commonly called the electroweak force? I know that it's not an everyday occurance that they merge into the same force since it takes a lot of energy. I'm sure there's people who know way more than I here but I figured I'd chime in just in case. feel free to delete this if it's total nonsense. --some anonymous guy 07:27, 1 September 2006 (EST)

Ya, my history book says that they are the same but it requires a lot of mathematics to understand it. 68.155.149.13 18:00, 23 February 2007 (UTC)

The electroweak interaction is part of the attempt to create the theory of everything used to combine the four forces in the standard model. The two forces diverged when the universe was approximately 1 second old and at a temperature of about 10^9K. It is appropriate to describe the four forces as seperate for the current universe (temperature about 3K) MDoggNoGFresh 16:32, 30 May 2007 (UTC)

Units

Can we assume that in the formula, r is in meter, m in kilogram and F in Newton? If yes, I'll just add this precision. JeDi 11:51, 7 September 2006 (UTC)

It is in any units you like, provided that r has units of length, m of mass, and F of force (or, equivalently mass*distance/time^2). G has units of exactly what it has to—length^3/(mass*time^2)—and of course its numerical value depends on the system of units used. But the point is, since the units balance on both sides, this equation (like all fundamental equations in physics) is not dependant on a particular system of units. -- SCZenz 20:24, 7 September 2006 (UTC)

First paragraph

Shouldn't it say something about gravitation being a theory in the first paragraph? Maya Levy 13:16, 11 October 2006 (UTC)

I don't understand what you're getting at, but I think that the first paragraph is pretty bad. I'm going to rewrite it. --Smack (talk) 16:35, 15 October 2006 (UTC)

The first line reads: "Gravitation is a phenomenon through which all objects attract each other". The sentence is false since object don't attract each other. We know that since 1915. It was an old prejudice born out of efforts to explain Newtonian math, which even Newton himself considered sick. I don't think we should start a wikipedia article with an old and sick prejudice.

The gravitational force is an inertial force that looked to most of 18th, and 19th century physicists as "attraction". It could be explained at the beginning of the article why it is an inertial force and why it looks as attraction if one doesn't know where to look. To bad that someone replaced my old stuff with the old (according to Einstein) and sick (according to Newton) prejudice instead of just showing how gravitational force is determined according to Einstein. Jim 11:22, 21 November 2006 (UTC)

Equations for a falling body

I heard about a hungarioan who said intresting things.

"[...] A motivation of the author to an experiment checking the UFF hypothesis in a range of pro mille, in a simultaneous free fall from 110 m fall height in vacuum with different materials, found mainly on the three “irregular” observations:
1) The observed values of G are widely scattered. For instance considering the measurements after 1995 only, the deviation of G is 0.7%. → The quantity G = G m g / mi does not appear as a constant in measurements.
2) A recalculation of Kepler’s third law by Szász with all the nine planets has discovered a composition dependency up to 0.15%. → The motions of planets are composition dependent and violate the UFF.
3.) The relative mass defects of isotopes MD A Δ offer a dependency from the mass number A up to 0.78%, Audi and Wapsta, Ref. [11]. → In microgravity, there is a loss of mi A and the change of MD A Δ depends on the number of nucleons. The Newtonian would be G = G M g / M i mg /m i ≈ G (1+ MD Δ (M)+ MD Δ (m)) Prior to the description of the experiment performed never before, the theoretical background, which is extensively [...]" "[...]
Simultaneous Fall Experiment with Different Materials from 110 m Height

For an experimental verification of the difference between the inertial and the gravitational mass, the author has used only solid chemical elements Li/Be/B/C/ Al/Fe/Pb and has performed a simultaneous fall experiment in the 110 m high vacuum tube at the drop tower of ZARM, University of Bremen. The weights of the test bodies were between ~2 g and ~7 g. The purities were better than 98.8% in all cases. The test bodies were freely placed at the middle of the safety glass cylinder. On the back plane of the experimental equipment, a cm scale was fixed with 0.0 cm at 130 Measurement of UFF Violation with Li/C/ Pb Compared to Al start, and with red marks for the fall distance prognoses according to Eq. (5). The relative movement of the test bodies was recorded with a standard CCD video camera. The camera was placed in front of the middle glass cylinder through a mirror arrangement in a distance (from the front of objective to the cm scale on the back ground) of ~ 60 cm directed to the height of 15 cm. The experimental equipment was fixed in the drop capsule falling freely in vacuum. The time resolution 0.04 s is to be calculated from 25 frames/s. From 256x256 pixels, the space resolution is in order of 1 mm for the quickest relative motion of Li. The time of fall was mirrored in by film exposure in 40 ms units. The time of fall with approximately free fall conditions and the relative fall distances in each time step can be read immediately from single pictures of film. The following sequence of four pictures shows the relative movement of the seven test bodies at fall times of 1.23 s, 2.43 s, 3.63 s and at 4.68 s, the end of the 110 m fall. [...]"
Any comment? (Nemethpeter 18:54, 26 October 2006 (UTC))

To verify these results one would need more data. E.g. how good the vacuume was, the shape of the falling bodies, method of releasing them, etc. It looks like the experiment (or the reporting) has been done by amateurs while professionals have done them with meassurements of many orders of magnitude more accurate and didn't find any diff between Newtonian equations and the real world. So your results didn't look like worth analizing, however if you don't mind, get the missing data and calculate what is the expected standard deviation. It'll be a nice exercise and you will learn something at the same time. Jim 14:28, 21 November 2006 (UTC)

I think this discussion was wrapped up nicely on my talk page. The gist of it was: 1)not enough sources; 2)all results quoted were the accepted value to within experimental uncertainty. --MOBle 17:41, 21 November 2006 (UTC)

Einstein's Jewish Heritage

Somewhere in the article, it says that Einstein was German-born. Recently, someone added that he was Jewish after that clause. It was quickly reverted. I think it should stay, for two reasons:

The sentence said that Einstein was German-born. That fact that he was of Jewish descent had very serious consequences for him, even before the rise to power of the Nazis.
He identified himself as a Jew — a nonreligious Jew, but a Jew nonetheless. He left his personal papers (and other things, I think) to the Hebrew University of Jerusalem, and generally seemed to be proud of his heritage. I don't think we should play revisionism.

It might make sense to remove both "German-born" and "Jew", but I think that if one stays, both should stay, because they are so essentially intertwined. --MOBle 12:59, 13 November 2006 (UTC)

I would support the removal of both. The detail impresses me as being inappropriate to an overview article such as this one. If nothing else, this article is about gravitation instead of Einstein, although if there is a guideline that says that the first reference to a physicist should include their country of origin and religous affiliation I would yield to that. It also seems to me that the details of who Einstein was are covered more than adequately in the Albert Einstein article. --EMS | Talk 19:39, 13 November 2006 (UTC)

Done. --Ancheta Wis 00:32, 14 November 2006 (UTC)

Missing Einsteinian equation for the gravitational force

In the whole article as well as the linked to it an article on general relativity there is no Einsteinian equation for gravitational force nor any instruction how to calculate it. So what a high school student is going to think about Wikipedia if he is looking for explanation of gravitational force? That Wikipedians think that Newtonian stuff is good enough for him? Maybe this is what most of them think but is it right thinking?

Furtheremore there is the following item counted as achievement of general relativty:

The expansion of the universe (predicted by the Robertson-Walker metric) was confirmed by Edwin Hubble in 1929.

Edwin Hubble didn't "confirm the expansion", he only proposed a law that redshift of galaxies changes linearly with their distance form us. Which was wrong anyway since Einsteinian physics predicts exponential change which simulates accelerating expansion. Anyway, since this item is wrong I propose to replace it with

The 'anomalus' acceleration of space probes Pioneer 10 and Pioneer 11 has been predicted by Einsteinian gravitation within less than half standard deviation (this is still an original research but it might be not anymore probably earlier than Wikipedians reach a consensus on what changes should be made in Gravitation). Jim 11:51, 21 November 2006 (UTC)

I seriously doubt the conclusion you just stated. However, regardless of my doubts, you need to find a reputable source for your statement. --MOBle 17:41, 21 November 2006 (UTC)

There are a number of things wrong with this the initial message here:

In general relativity, gravitation is not due to a force. Therefore there is no equation for gravitational force in general relativity.
Gravitation is of course not due to a force but it does not make general relativity (GR) unable to calculate a gravitational force that acts eg. on a guy standing on the Earth. If you mean that GR is not able to calculate this force you simply don't know basics of GR and you are not someone who can instruct people on what is right and what's wrong in gravitation. The way to calculate gravitational force in GR is this: take invariant energy of a guy (from any textbook on GR, for the mass of the guy of course) differentiate it with respect to guy's proper distance from let's say surface of the Earth (standard for calculating "forces") reverse the sign and your result is the gravitational force with which the guy acts on the Earth. Then you will also see why it is only an inertial force and not some mysterious attraction as 19 century thinkers call it. Pretty simple derivation and I don't see it anywhere in whole gravitation page as if it never existed and I remember well placing it there. GR would be a very poor theory if it didn't allow to calculate in a simple way, that a high school student can understand, a gravitational force. The calculation is in fact so simple that is shown mostly in popular texts (like mine) since professionals don't bother with high school calculus. Which does not mean that high school calculus is useless and can't be used in a standard way to calculate forces. Jim 11:49, 25 February 2007 (UTC)
While there is gravitational accelaration due to spacetime curvature, what describes it is a tensor expression known as the Einstein field equations (EFE). This equation can be written as $R_{\mu \nu }-(1/2)g_{\mu \nu }=8\pi T_{\mu \nu }$ or abbreviated to $G=T$ , but those are most uninformative to people who lack an understanding of tensor calculus.
The instructions for calculating gravitational interactions starting from the EFE are hideously complex and do not belong here. See general relativity resources for textbooks and web sites that can help with this.
One differentiation of energy of a particle is "hideously complex"? Jim 11:49, 25 February 2007 (UTC)
Solutions of the EFE such as the Schwarzschild solution could be used instead of the EFE. There is still a need to use tensor calculus with them however, and links to articles on the relevant solutions are already in this article in any case.
Hubble's observations did confirm that the universe is expanding as predicted by the Robertson-Walker metric. Kindly note that accelerating expansion of the universe is a result of modern observations! It can be described using an EFE solution, but is not a unique prediction of general relativity. (Note that the enabling EFE solution requires the universe to be 70% dark energy, 26% dark matter, and 4% normal matter. So the acceleration is being used to predict to composition of the universe and not the other way around.)
General relativity does not account for the Pioneer anomaly. The difference between the Newtonian and GR preditions is just way too small.

Overall, this article is about gravitation and not GR. For more information of GR, you are advised to follow the links provided. --EMS | Talk 19:26, 21 November 2006 (UTC)

Come on. One doesn't need tensor calculus to calculate gravitational force. Simple differentiation of energy of a particle (like in Landau and Lifshitz, Theory of Fields, eq. 88.9) with respect to distance, suffices. Elementary high school physics. Every high school student who wants to know how gravitational force is generated in Einstein's theory may learn it in 10 minutes. The problem is though that whenever the derivation of gravitational force is placed in wikipedia someone who has never seen it before, considers it original research and replaces it with Newtonian "force". So the high school students tend to believe (as it is stated at the beginning of the article by some 19 century thinker) that gravitation is a phenomenon through which all objects attract each other. So unless editors start learning 20 century physics nothing can be done. But once they do the high school students see how simple Einstein's physics is and the only problem with it has been that editors of wikipedia haven't understood it a bit, since (as the same Landau said) it's tough to explain things that one doesn't understand himself. Jim 22:31, 23 February 2007 (UTC)

Let's get back to the question that was thrown out of the article section, If I'm in a geosynchronous orbit around the earth and I see two objects dropped near the north and the south poles and I see them falling towards each other, am I supposed to attribute that phenomena to the curvature of space? I can see your moving towards minimum energy concept but I dont see what the three dimensional space continuim has to do with it.WFPMWFPM (talk) 17:13, 16 June 2008 (UTC)

Question about gravitation for the article

A question of mine that might be interesting for the article: when two bodies impact each other and join they become one with a single gravitational field, but what if they are just touching? What if we have a 50 km asteroid and a 100 m asteroid is made to touch down gently on the surface? Does just touching the larger one increase its gravitational field or does it require something else? What is the exact borderline for when objects become one in gravitational terms?

Mithridates 15:59, 11 December 2006 (UTC)

Semantically, that is a question for astrononmers. In terms of the gravitational field, the farther you are from the object (objects?), the more appropriate it becomes to treat them as one object of the combined mass instead of two objects. Thus holds true even in the objects are in orbit about each other. (For example, to model the trajectory of a spacecraft in Earth orbit you would consider the Moon as a seperate object, but to model the orbit of Pluto it is fine to treat the Earth/Moom system as a single mass unless your calculation were are extremely high precision.) --EMS | Talk 16:41, 11 December 2006 (UTC)

Good question —The preceding unsigned comment was added by Makewater (talk • contribs) 19:45, 16 December 2006 (UTC).

This is a question of philosophy rather than science I think. There is only one gravitational field (or if you prefer to talk about relativity, only one curvature tensor) for the entire universe; at each point, it describes the amount of force exerted by gravity (degree of spacetime curvature, which causes objects to move) at that point. The gravitational field due to two objects is just the superposition of the fields due to each alone; as they collide, that field looks more and more like that of one larger object. When it "officially" becomes two objects rather than one really just depends on how you want to look at things in a given problem. -- SCZenz 23:06, 16 December 2006 (UTC)

One quick comment:

I don't think it's a verifiable fact that Galileo dropped anything from the Tower of Pisa. As far as I understand most historians consider that an urban legend, seeing that Galileo would generally be very specific in his observations and therefore it would be a very unprofessional experiment. Any thoughts?

Yuri

Existence of Gravity

These needed to be added to the article, or made so they stand out and are understandable to the user, because even i am left w/ these questions:

1 Can Gravitation be proved?

2 If so, is there a way to prove it other than mathematically?

3 If gravitation is real, what is it? Matter? If not, is it actually in existence? (dont bring in philisophical/religious stuff in, i.e. "spirits exist, so gravity can")

4 Why the gravitational theory is a theory and not a fact/law.

toaster 02:05, 6 February 2007 (UTC)

I can tell you that gravitation is an observed fact. After all, the planets go around the Sun and we are constantly pulled downward towards the center of the Earth. In essense "gravitation" is the name of an observed phenomenon.

As for "proving" gravitation: You don't do it mathmatically to begin with. Instead it is the observation that matters. A combination of math and observation comes in when one seeks to verify that a given theory of gravitation is correct. In fact, this also brings up to your last question, since any explanation of gravitation is just a model and not the reality. Even if a given theory is exactly right, there is no way from first principles to prove that gravitation must exist and have exactly certain properties. Given that, any theory of gravitation must be just a theory due to its carrying with itself its own postulates. --EMS | Talk 20:12, 7 February 2007 (UTC)

Point four is best addressed by reading theory; theories are like the existence of God - they can never be proven. Unlike God, they can be disproven. And as far as I know, they still don't know what causes gravity, there's just the whole 'bending of spacetime' thing. Gravity is still very poorly understood as a phenomenon, though it's effects are well known. WLU 23:59, 7 February 2007 (UTC)

Ok, but than what can we say gravitation is, but not just the simple attraction between two objects? Heck, what other observable phenomenon out there does not have matter?toaster 22:26, 8 February 2007 (UTC)

I'm not sure I understand the question, but WP:OR, we can't speculate. We can't put anything beyond what's documented in secondary sources. Gravity will not be solved on wikipedia. WLU 00:54, 9 February 2007 (UTC)

Why not? If the knowledge about Gravity, a simple direct inverse-square of distance force, seems to have been already unveiled (an electrostatic force):

"I must admit that what emerged from my theory, in allowing me to derive the constant of gravitation G by pure theory, plus the fact that physicists have taken it for granted that gravitation and electrodynamics would one day be connected by a unified field theory, seemed conclusive. (...) However, the day came eventually when I saw how to derive the Neumann potential starting from Coulomb's Law and that involved a step which I now see as destroying the case for the force of gravity being electrodynamic in origin." by H. Aspden, 2003

and if G, the constant of gravitation, seems to have been already derived (6.67x10^-8 dynes.cm².gm^-2) in good accord with its measured value; and if this research is partially mentioned at this page and fully published online, plus if the major past efforts to understand Gravity are of record in Wikipedia's physics pages: why not make an effort to solve its validity here? (at a time when those in charge seem to have not the Will to solve it in the "scientific laboratory": how could they? to throw a whole century of proud and loud scientific theories into the "recycle bin" [be it the 'four-space', the 'black hole', the 'big-bang', popular physics and cosmology literature, high personal and academic honours and titles, or the vast expenditure in high collisions experiments creating freaking forms of matter, etc.; all of these in order to have understood too little or even no-thing about Mother Nature...])?!

WP:OR. Wikipedia does not solve problems, WP reports on problems already solved. WLU 02:12, 11 February 2007 (UTC)

He doesn't want a problem solved, he just needs answers to the questions. If someone could supply him with that i think it would make him feel better.63.215.29.113 19:53, 3 March 2007 (UTC)

How to teach editors gravitation?

Whenever one tries to replace statements of Newton's gravitation with corresponding statements of Einstein's gravitation the editors reverse the changes. Often without any good reason beyond a vague impression that it might be original research. As it happens to me a lot and they don't even answer a question what they consider original research. While I'm only trying to popularize Einstein's theory and everything I write Einstein already knew. However not editors of Wikipedia. Which is rather sad because it's almost a century of ignorance.

And this reversing is probably not because they want to prevent Wikipedia users from learning gravitation. Most likely the reason is that they don't understand a bit about gravitation and think that Newton's theory about it, which they remember from school, is science. They think that Einstein's gravitation should be close enough to Newton's and ignore the fact that while it is (almost) the same math it describes a completely different physics. So whatever is not close enough to Newtonian physics should be deleted. Even something like derivation of a gravitational force because it can't be derived with Newton's theory. They don't know how to derive it so they suspect it of being never derived even by Einstein (otherwise how it could be close enough?). They must assume that Einstein discovered theory of gravitation without addressing the issue of gravitational force. It might sound funny but this is really the case with most editors. Which is telling us that some of them must be intellectually challenged yet they keep editing Wikipedia and that's why Wikipedia is so much retarded in the area of gravitation. And that's why there is a problem with editors which better be solved. Jim 22:20, 24 February 2007 (UTC)

Jim, here is a candidate --Ancheta Wis 08:31, 26 February 2007 (UTC):

First and foremost one MUST consider velocities origins for a given force, having done this for gravities force, wouldn't gravities attraction be better described as a perception rather than some magical force?

Yours,

Peter J Schoen.

Hi Ancheta, good candidate :-)

But what to do with those more agressive ones who never heard that Einstein's gravitational force is inertial (pushing not attracting) and when they see a force that is not attractive they replace it with Newtonian attraction, F=GMm/r^2) insisting that it is good enough for them?

I tried to educate one of them showing him how gravitational force is derived in Einstein's gravitation. It was lost on him due to his lack of interest in Einstein. And unfortunately he's not alone in this. Many of them don't even know that with Einstein's gravitation one can calculate gravitational force (!).

Are the users of Wikipedia going to be fed 300 years old gravitation forever or is there a way to stop it? Jim 18:38, 2 March 2007 (UTC)

Jim - All that you are doing is showing that you do not understand general relativity either. In general relativity, there is no force of gravity, but instead a curved spacetime such that objects which are neither being pushed nor pulled are directed towards massive objects. So the bottom line is that this article is not going to be amended to suit your desires, as your views are just plain incorrect. --EMS | Talk 04:12, 3 March 2007 (UTC)

Dear EMS, when you're standing on the Earth there is a force that is pressing you to the Earth. It is called by physicists in my university (and by a little me as well) a gravitational force. How do you call it? And how do you think Einstein had called it?

Can you explain this force and calculate it from the curvatures of sapacetime in a way that a high school student can repeat your derivation from memory (as I've done many times, just using text from 1973, Landau and Lifshitz) and make the derivation stay in Wikipedia for more than a week?

As for your strong opinion about gravitational force you are probably saying that there is no such force between objects that are not in contact with each other (i.e. that this force does not act at the distance) which is surely true but nobody except all those Wikipedia editors say there is such a force so it is irrelevant for the purpose of educating high school students in contemporary physics. Jim 17:05, 3 March 2007 (UTC)

Has anyone seen JimJast's questions to all the board candidates? Can you believe this guy? Either he is a complete idiot, or he is speaking a language other than English (a bizarre language known only to Physics PHD students), or both. Just accept that gravity is the natural force that attracts massive objects to each other, as any kindergarten student can prove. This is not the place for writing your PHD thesis. This is an encyclopedia for ordinary people who speak English. Gravity is a remarkably simple concept. The total unreadability of all the scientific articles in this Encyclopedia is entirely the fault of scientists such as JimJast who are unable or unwilling to speak normal English or to recognise that the average editor knows a fair bit about the subject. The next person who says a line is not a line because it isn't infinately long should be made to swallow a dictionary. Carl Kenner 13:10, 5 July 2007 (UTC)

I have taken a look at it. Overall it is nothing but the same self-serving bellyaching that I have seen in other contexts. For now, I will place Jim Jast in the "a little knowledge is dangerous" category. As for the candidates, one has made a blanket statement that shows no research into this matter, another that I looked at called on Jim to work with us, and the overall majority seem to have enough sense (or lack of time) to not respond at all. Let's just say that I have a hard time faulting those who don't respond.

As for the science writing here: The problem is that more editors are needed who are interested in this stuff, and who appreciate Wikipedia for what it is. Much here is written by experts, and unfortunately reflects that. This creates an ironic situation whereby the the process if improving Wikipedia means that many articles must be "degraded". An example of that ironically is Jum's edit: I actually have some sympathy for it's intent (being a general relativity person myself). However, Wikpedia is for everyone and not just Ph. D.s. That is why I agree with you about keeping the definition of gravitation simple, but do note that I for one refuse to allow the word "force" to appear in the first paragraph due to Einstein's work. --EMS | Talk 04:40, 6 July 2007 (UTC)

POV fork (?)

A couple of days ago, User:JimJast changed the term gravitational attraction from a redirect to "Gravitation" into an article of its own. I don't know whether such a separate article is required, or maybe the things should be included in the existing articles on gravitation, but the main problem is that User:JimJast dedicated that article to a philosophy of his own (starting the definition with the words "gravitational attraction is a myth", and later saying "There are no gravitational forces between particles that are free to move as e.g. between the stars and the planets of the universe"). I tried to make the article more balanced, and discussed the issues with User:JimJast on the Talk page, and presented references (including a textbook) showing that there are well-established alternative ways to look at the subject, and his general statements are incorrect. Nevertheless, he reverted most of my edits, and put his wrong ideas back. Please join the discussion. Thanks, Yevgeny Kats 21:09, 13 March 2007 (UTC)

I have reverted the article to being a redirect, and chastised Jim in the talk page. However, we will need to watch that page. JimJast is a regular troll here, who does not understand that difference between one's personal ideas and the accepted scientific viewpoint. He has been trying to push his odd ideas of talk pages for the last few months, and obviously thought that he had found an avenue here for presenting them in the article space. His original research is not acceptable here, but Jim obviously does not see his OR as being just that.

I looked at your edit of that article and did like it. Please feel free to use it to add to this article as needed. --EMS | Talk 16:37, 14 March 2007 (UTC)

Dear Yevgeny and EMS, Finally I looked at "Gravitation" Talk page (which I have no intention to edit since I don't have time to argue with editors who prefer faith over data) and I saw that you guys don't like GR and Landau's explanation of gravitational energy that I've put it on the page "gravitational attraction". Apparently you prefer gravitational attraction being real which is your right, however not allowed to be excercized in Wikipedia. So while you may be right, for the time being it is only your private POV since official version is still Einstein's. The point is you don't have yet any official theory to support your POV. That's the only thing we don't agree about: you think your POV is valid since you believe that the (future) quantum gravity is going to confirm it. I doubt, since I doubt in many things, but Wikipedia's policy of NPOV is clearly on my side here: don't push your POV until it is supported by a relieable source. For the time being GR is considered more reliable than quantum gravity. And this is not my fault so please be reasonable.

As to the "fact" that our feet are "attractd" to the Earth (as EMS suggests in line with your POV) then I explained it in the page gravitational attraction in agreement with Landau's equation provided there. Unfortunately both Einstein and Landau are dead so we can't consult them but their texts are still around and we can find out whether they believed in gravitational attraction the same way that you do. It is basically an argument betwen you and Einstein's. So please prove that general relativity (the actual theory of gravitation that Wikipedia is supposed to promote rather than quantum gravity that many other physicists prefer) supports your POV and not Einstein's and then we are all set. Jim 08:34, 15 March 2007 (UTC)

I find it hard to deny that there exists a gravitational acceleration between objects. Whether you wish to align the word "attraction" with "force" instead of "acceleration" is an interesting question, but the bottom line is that the phenomenon exists. Beyond that, you don't seem to understand Einstein's GR view on gravaitation, or at least have a very non-standard way of expressing it. I also find Landau's explanation to be quite cumbersome and unhelpful. Most treatments of mass in a gravitational field consider the mass as having decreased instead of c having done so (although that approach works too), and the use of the energy change as a cause of gravitational acceleration provides only a first approximation of how curvature causes particles to move. --EMS | Talk 15:34, 16 March 2007 (UTC)

Inertial Paradox?

This statement is not self-evident: "In flat spacetimes such as those of classical mechanics and special relativity, there is no way that inertial observers can accelerate with respect to each other, as free-falling bodies can do as they are each accelerated towards the center of a massive object."

Given Observer A and Observer B falling toward Mass C, the the statement implies there is no way for A and B to accelerate toward eachother. To me this says there is "no way" A and B can have a gravitational force between them (albiet small). Why not? What is the proof of this assertion? Dw31415 17:21, 23 March 2007 (UTC)

If a force is being exerted on them, they are not inertial observers. So in classical mechanics, that statement is moot. However, in general relativity, it is very, very important: In GR, there is no force that causes gravitation. So another mechanism (in this case spacetime curvature) takes the place of gravity and acts as the source of the gravitational field. --EMS | Talk 18:00, 23 March 2007 (UTC)

I don't think that paragraph in the article makes sense at all.

First of all, the sentence before the one cited above says: "inertial motion occurs when objects are in free-fall instead of when they are at rest with respect to a massive object such as the Earth (as is the case in classical mechanics)". It's incorrect to say that in classical mechanics a reference frame is inertial when it's attached to a heavy body. If the heavy body is accelerating, the frame won't be inertial. If the heavy body is rotating, the frame won't be inertial. Furthermore, a heavy body isn't a part of the story at all. An observer can be inertial even if he is very light and not attached to anything.

As for the sentence cited by Dw31415, that sentence is wrong too. Since bodies may be free falling with a different acceleration in different places (e.g., on opposite sides of the Earth), they will have an acceleration relative to each other.

Furthermore, I don't know if that new definition of inertial motion that is used in that paragraph is very standard. At least a definition should be given for what is meant by that. Yevgeny Kats 19:11, 23 March 2007 (UTC)

That sentence is of my devising. It is quite technical yet more-or-less says what I want it to say. You are correct that rotation and orbital motion keep the Earth from being a inertial frame is classical mechanics. Perhaps we can hash out how to correct that. The part about inertia in GR is unforutnately quite technical, but is also concise. I am open to suggestions on how to improve that also (or even that section). It may be that this is not the best place to make the point that I am trying to make, although I personally prefer to make it here. --EMS | Talk 20:08, 23 March 2007 (UTC)

EMS, I propose that the sentence be recast into subjunctive mood. --Ancheta Wis 10:06, 24 March 2007 (UTC)

For example "If a photon were ... then ...."

Thanks for taking a look at my concern. I think this introductory paragraph would do well to continue the thread of how this theory explains the Mecury orbit does not match what would be predicted by Newton's equations. After all that's the way one theory replaces another, right (the new one is consistant with observations that the old one cannot explain). Dw31415 04:28, 24 March 2007 (UTC)

If you are suggesting what I think you are suggesting, then I strongly advise against it. "[H]ow this theory explains the Mecury orbit ..." requires that use of a level of detail that I have largely avoided even in the general relativity article itself. In this article, I want to stick with the issues of "what", and leave the issues of "how" to other articles. (Maybe an orbits in general relativity article could go into the details, but that is going to be another project IMO.) --EMS | Talk 05:08, 24 March 2007 (UTC)

Dw31415, please, let's not use this page to segue to another topic. Please include a link to the next topic, so that this page stays focussed. See for example the featured article Laplace-Runge-Lenz vector --Ancheta Wis 09:58, 24 March 2007 (UTC)

I'm a Mechanical Engineer by training, so I spent four happy years with Newton and we worked well together. For the last 15 years, I've tried to find a coherent explaination of how Einstein and Relativity added a more accurate explanation of what type of phenomenum (sp?). One of my biggest frustrations is that the experts always go to some highly abstracted example (like you're falling in an elevator at the speed of light...). I think the opening paragraph is in that same vein. I think the opening paragraph should focus on real phenomenum first. Wouldn't Newton's equations properly account for the forces in the first example (two small masses and a big one)? Thanks again (And Ancheta, since I'm trying to get us to revise the transition between two theory's of gravity, this seems like the right place.) Dw31415 15:04, 24 March 2007 (UTC)

General relativity really is a very technical thing. That is not to say that I cannot do better in expressing what it is, but it is going to take some figuring. Here is a alternate explanation. Pull something together using it:

General relativity is a theory in which expains gravitation as being the result of spacetime have a curved topology. The central way in which general relativity differ's from Newtonian physics is in its definition of inertia. In Newton's theory, standing on the surface of an extremely large mass which is not rotating or being accelrated puts you in an inertial frame of reference with the downward force of gravity being balanced by the upward force from the resistance of the surface; while a free-falling object is only subject to the force of gravity. What Einstein realized was that the force of gravity being proportional to the mass of the falling object means that gravity is a fictitious force. This is turn means the free-fall is really a form of inertial motion, while standing on the surface of a massive object places one in an accelerated state of motion.

The identification of free-fall as inertial motion conflicts with Newtonian physics and also special relativity in that inertially moving objects cannot accelerate with respect to each other. (Note that in Newton's second law, all physical accelerations are due to a force.) However, side-by-side objects free-falling towards a planet are being accelerated towards each other (as they head faster and faster towards the center of the object); while when the objects are one above the other they will diverge (due to one being pulled on more strongly than the other). If free-fall in inertial motion, then these relative accelerations cannot be due to a force. The key to the issue is that both Newtonian physics and special relativity assume that space (or spacetime for special relativity) is flat. Einstein removed that restriction in general relativity, and produced a theory where inertially moving objects can accelerate spontaneously due to the shape of spacetime.

I have a feeling that I am saying too much and too little here. You comments would be appreciated. --EMS | Talk 21:38, 24 March 2007 (UTC)

I have done some tweaking of this article to better communicate what GR is. Please let me know what you think of the changes. However, please do be advised that GR is not a simple topic, while this article necessarily must be an overview on the major theories and issues involving gravitation. The places where greater accessibility would be helpful are the introduction to general relativity and the general relativity articles. --EMS | Talk 02:03, 26 March 2007 (UTC)

I'd say it's better now, but still not completely satisfactory. The sentences

The issue that this creates is that free-falling objects can accelerate with respect to each other. In Newtonian physics, no such acceleration can occur unless at least one of the objects is being operated on by a force (and therefore is not moving inertially).

are somewhat problematic. The first sentence may give an impression that free-falling objects can't accelerate with respect to each other in Newtonian physics (which is certainly not what you meant; you wanted to say something like "in general relativity, inertial observers can accelerate..."). Also, I think it's not really clear what point you're trying to make, e.g., why the inertial observers are defined differently and what's the importance of that. The answer is something along the lines that in general relativity the physics is described in the same way not only by inertial observers, but by any observer, including the accelerating ones. Yevgeny Kats 02:34, 26 March 2007 (UTC)

I will think on what I can do here. I can see where some rewording will help in communicating the intended meaning, but have not yet figured out what that should be. The fact that I am assumming the general principle of relativity here without stating it or something similar may or may not be a serious issue. When you are faced with having to put 10 pounds of it into a 5 pound bag, something has to give. This can only be a concise but accurate statement of what GR is at best, which hopefully will help to point the reader in the right direction if they should care to read more in the related articles. --EMS | Talk 03:11, 27 March 2007 (UTC)

Improving "gravitaton" page

Hi Everybody. Recently the page "gravitational attraction" where I expained the nature of gravitational attraction got redirected by vote 9:1 to "gravitation" that unfortunately contains inaccuracies in its desription of nature. So, since it seems that we have no much choice but to explain the gravitational attraction in "gravitation", we need to clean up the page to reflect what about gravitation is published in reliable sources.

For that reason whatever is contradicting the contemporary knowledge of gravitation in this page has to be changed to whatever reliable sources say about real gravitation rather than what some editors put for whatever reasons into this page. The first thing that I propose to change is the opening sentence "Gravitation is a phenomenon through which all objects attract each other" since this is neither true nor reliable published source says so. It turns out that in our universe (as proposed by Einstein and we have to stick to it for already explained reasons) no object attracts any other. The alleged attraction is an over three centuries old prejudice, believed in also by many physicists, apparently for wrong reasons, since they couldn't come up yet, after so many years of trying, with consistent theory of quantum gravity. It should be finally explained why the behaviour of objects looks as they were attracted to each other. Between other things to allow those physicists to understand gravity better.

Before that though I propose to change this opening sentence back to what was there which read something like "Gravitation is a phenomenon through which objects tend to get closer to massive objects in their vicinity". After reaching an agreement on this first change we explain why they look as if they were "attracted" to thoses massive objects, as I did it in my redirected page. For now I'd like to have your agreement to this first change (which I expect knowing your opinions about Einstein might need some debate) and if the consensus is reached we might go on with this first and then with further improvements until we fix all the problems. So please express your opinions about this project. Jim 23:53, 25 March 2007 (UTC)

A couple of comments to Jim:

1. Wikipedia isn't a place to do revolutions in the way knowledge is commonly presented, so I think it will only be agreed that your suggested approach will reflect itself only in slight changes to the wording of this article (if necessary at all) and/or a few comments (again, if they aren't there already). Note also that the decision was clearly redirect rather than merge (and many editors there specifically opposed the contents of that article) so you'll need a good consensus in order to implement your suggestions here.

2. I think your suggestion for the first sentence is very awkward. Using the word "attraction" is very standard, and Wikipedia isn't a place to suggest changes in the language. Furthermore, I don't think using the word "attraction" is incorrect.

(a) Main reason: The phenomenon we're talking about is known as attraction because it behaves as attraction.

(b) Secondary reason: You can describe exactly the same physics of general relativity in the mathematical framework of quantum field theory as we discussed here (including several reliable sources), where the attraction is real (mediated by graviton exchange, not spacetime curvature), as real as the electromagnetic attraction (that is mediated by photons). Note also that this doesn't depend on the theory of quantum gravity (which might not be a field theory at all: string theory isn't a quantum field theory), as I already mentioned there. So please don't repeat that as a counterargument. Gravitons in quantum field theory are a well-established concept (e.g., according to the citation you yourself brought from Zee's textbook), even though the theory of quantum gravity isn't known yet. As for your intention

to allow those physicists to understand gravity better

I appreciate your help (and I'm sure that Zee, Weinberg and Feynman that I gave as sources will/would appreciate it too :)) Yevgeny Kats 01:39, 26 March 2007 (UTC)

Hi Yevgeny, "attraction" is of course an abbreviation for "force of universal gravitational attraction". Since, as you correctly noticed, "Wikipedia isn't a place to do revolutions" we should concentrate first on finding a reliable published source that supports the idea that there is such a force in nature. Once we find it we are all set. However Newton didn't believe in such possibility (for his lack of faith in action at distance (physics)) and even less Einstein (for the same reason) so we may have problems with this finding. Zee, Weinberg and even Feynman hoped for finding particles of spin 2 carrying that force but unfortunately didn't produce yet reliable published sources that we could use as Wikipedia requires. So if we won't succeed what choice do we have as to admit that Newton and Einstain might be the only reliable published sources? And then the change of "gravitation" will be forced on us by Wikipedia's strict policy that can't be changed by a consensus even if we love "gravitational attraction" as over 99% of population. So much that it is already included in urban legends of our time. So let's go to work and find reliable published source that supports the idea of gravitational attraction being real. We may wait five days for suitable candidate to show up and then we either leave "gravitation" as it is or correct it according to Wikipedia policy, regreting that new ideas are so difficult to implement here. Is it a fair solution in your opinion? Jim 06:49, 26 March 2007 (UTC)

Jim - I second Yevgeny's comments, especially regarding the meaning of "attraction". If I was to change the wording in the lead, it would be to say that each mass causes all other masses to be "accelerated towards" itself. However, I would want to see a consensus expressed for such a change before it is made.

I must admit that I have found your comments to be so strange that I for a while doubted that you knew relativity theory at all. Even now, you are making remarks that raise red flags about yourself: I have yet to see an editor insist that their view is mandated by "Wikipedia policy" who is not in fact going against said policy. Einstein and Newton are only primary sources, but WP:RS calls for the use of both primary and secondary sources, with the secondary sources being accepted texts which elaborate on the primary sources such as MTW, and Wald's "General Relativity" amongst others, and prbably a whole set of books of classical mechanics that I am not familiar with due to my focus on relativity theory. I do not see your viewpoint as being Einstein's view, but instead as being your view of what Einstein's view is, which is not acceptable. Instead, it is the consensus of the scientists in the field that matters here, and I see no evidence that said consensus is being misrepresented here. --EMS | Talk 13:28, 26 March 2007 (UTC)

EMS - "all other masses to be 'accelerated towards' itself" isn't a good wording. I propose "Gravitation is a tendency of objects to get closer to each other". It is neutral on the controvercial subjects of "attraction" and "acceleration", even regardless of what one means by them. Later the reasons for "getting closer" might be proposed as "force of gravitational attraction" or "shape of geodesics in spacetime" with an addition about which theory is supported by the contemporary science.

If you don't understand something then quote the unclear fraze and ask the author what he meant. It's faster then reporting your feelings and expecting the author to guess what you mean.

Recommending something like MTW is a good thing. I myself have read it a few times already and I still have it so it's easier for me to check it. The same goes for Wald's book. However I don't remember all of it, so if you find there a support for "attractive force" let's use the appropriate quote since both are considered reliable sources describing a contemporary gravitational theory. Jim 16:42, 26 March 2007 (UTC)

I can't say that I like "getting closer" since a body in an elliptical orbit gets closer and then father away. IMO, you are attaching to the word "attract" the connotation for "force". I don't see it. I can see why others will see that word and assume that a force is being referred to, but I don't see any utility in trying to communicate the fundamentals of GR to people in the lead. Let GR be implied there, and let people read in the GR section that the attraction is not due to a force. If they cannot handle that, then so be it, but don't try to tell them that "the force of gravity does not exist". I agree with what you are trying to say with that kind of statement, but most of the readers of this page will assume that you are ~~a vandal who is~~ denying the physical reality of gravitation. That just plain is not good. --EMS | Talk 17:03, 26 March 2007 (UTC)

Whether one uses Newton's theory, or knows about general relativity, or doesn't know either of them, "tend to get closer" = "attract". There is nothing else implied by the word "attract", so there is no reason to switch to the awkward formulation "tend to get closer". Yevgeny Kats 18:10, 26 March 2007 (UTC)

From Wikipedia: Attraction: In general, attraction is a force that moves one object to another. E.g. if a car hits a tree, which is similar to a colision with the Earth when somthing drops form certain hight, no one would assume a force pulling the car towards the tree, and consequently no one would assume some kind of attraction between the car and the tree. So why to assume something like that in a case of something dropping on the Earth? The only reason seems to be a Newtonian prejudice that the Earth "attracts" things. According to general relativity the collision between the car and the tree is the same kind of collision as between something and the Earth. No attraction in neither case, just crossing of worldlines due to other reasons. The encyclopedia should clarify prejudices in a spirit of contemporary science. Don't you agree that the first sentence of the present form of "gravitation" supports a traditional prejudice? Jim 14:49, 27 March 2007 (UTC)

First of all, I am loathe to consider Wikipedia to be a reliable source in so far as the issue of the meaning of "attaction" is concerned. Secondly, when a woman attacts a man, there is not a physical force involved. So the word generically does not demand a force. IMO, the bias that you are fighting is the Newtonian one that any observed acceleration must be due to a force acting on either the observer, the observed object, or both. You are not going to deal with that by saying that the force of gravity does not exist in the lead. Instead, you would confuse everyone not familiar with GR. Besides, under WP:NPOV, it is not the job of the encyclopedia to rule on gravity vs. GR. Instead, it is the job here to present the facts in as unbiased a means as possible. First of all, please note the title of this article: It is "gravitation", not "gravity"! Whether the reader realizes it or not, the name that reads "force" is not the title of this article. Then read the first sentence of the GR section, where I state right off the bat that GR does not ascribe gravitation to a force. Finally, note the large number of observations cites as proof the GR is right and gravity is not. In the end, the message that you want people to get is there. It just is not being announced out loud in the lead. Personally, I think that the article is much better that way. --EMS | Talk 15:28, 27 March 2007 (UTC)

As I expected we can't move beyond the first sentence yet :-). So let's do it slowly:

Please list all the features that make this article better than my version.

My objections to the article are that it is about physics but it is not following the physics since in "Gravitation" page there is no attraction in a physical sense, as a force, but rather in a psychological sense as a woman attracting another woman (both "attracting" masses are of the same "sex"). It does the "attraction" without any physical force since physical force is only in Newtonian gravitation and we already know it is wrong. Your standard of making the article much better seems to be only that the Newtonian prejudice of the reader about gravitations are confirmed and he's not shocked by learning that what he learned in a high school is actually wrong. In my opinion the reader needs this shock to appreciate the change that physics went through since 19th century. Jim 23:19, 27 March 2007 (UTC)

I just read the "General relativity" and "Introduction to general relativity" pages. IMHO, the problem with "Gravitation" page (correct me if I'm wrong) is that no one writing about it understands the simple Einsteinian physics behind it. The editors are trying to push into those pages all they know about the math forgetting that it has no meaning for those for whom encyclopedias are written. Consequently the gravitation remains a mess, a mystery to the readers, to the editors, and even to many non familiar with GR physicists. In short a bad popularization.

In particular, I didn't find in those pages an explanation of so called "gravitational attractive force", why it looks like "attraction", why it is really a pseudo force, how this pseudo force it is generated by the curvatures of spacetime (the thing that I put into "Gravitational attraction" page and it was removed from Wikipedia by 9:1 vote on a theory that it is my private POV (and possibly Landau's private POV, not acceptable to Wikipedia editors). Where this information on physics of gravitation is located in those pages? Jim 19:25, 28 March 2007 (UTC)

Are you reading the same Wikipedia as the rest of us? I foudn the following line in the first section of "Introduction to general relativity"

... the gravitational field we feel at the surface of the earth is really a fictitious force like those of other non-inertial frames of reference.

Furthermore, this was preceeded by a number of examples helping to make the point that you want made. It seems to me that what is "missing" is your prefered POV on this issue instead of the point itself. --EMS | Talk 20:59, 28 March 2007 (UTC)

I was reading the same Wikipedia but I don't think it explains physics (forces, energies, and stuff like that) that high school student can understand. I treated seriously your call for making this page less mathematical and I'm now waiting for your appreciation of my job. However it might need some beautifying since not all high school students might understand what we do and certain things might need to be explained to them more clearly and with simpler language than just a language of regular calculus. But I think that as for an introduction it is a proper way of doing things. Because they can go to "GR" page ind got stuck there for the next 15 years until they understand everything. Even why the universe isn't really expanding in Einsteinian physics and why it is all just another illusion, like many other things in science. Jim 22:11, 28 March 2007 (UTC)

Just for the record

The passage below was labeled as 'pseudoscience' by a 'state-of-the-art' expert, physics graduate student of the oldest U.S. university, expressing the common materialist-positivist-reducionist approach of the 20th century academic thought applied to the long-standing but avoided work, into the ancient subtle aether, by a former student of the second-oldest university in the English-speaking world:

Deleted from section "Gravity and quantum mechanics" > 01:46, 31 March 2007 Yevgeny Kats (Talk | contribs) (Undid revision 119178843 by 213.58.99.45 (talk) (pseudoscience)):

and a few believe that a complete quantum theory of gravitation, along with a whole new physics, is already being provided by the modern aether theory (ref: Aspden, Harold (2006). Creation: The Physical Truth. Sussex, England: Book Guild Ltd. ISBN 1846240506.).

Removed afterwards, for coherence reason, from section 'Newton's theory of Gravitation' > 01:55, 31 March 2007 213.58.99.45 (Talk) (→Newton's theory of gravitation - If you, expert, say so, then the same applies to this passage supported by the reference work of the same author ():

However, it is currently known that the theoretical formula for the anomalous perihelion motion of a planet, such as Mercury's perihelion, can be derived solely based on an extremely simple proposition founded in classical physics (ref: Kidman, J. N. (1977). Quantum gravitation and the perihelion anomaly. Lettere al Nuovo Cimento, 18, pp. 181-182. "on-line" (PDF). (91.1 KiB)) without the need of any excursion into Einstein's space-time notion.

Let us see what the true Science in the future, be it in 50 or in 500 years from now, will have to say regarding this auto-proclaimed 'scientific-knowledge' age of our human history. As a great Mystic in the U.S. once wrote "The man who realizes his ignorance has taken the first step toward knowledge." Cheers.

Hey there, thanks for your comment! I'd like to note that according to Wikipedia policies, decisions shouldn't be made just according to the opinion of editors who are "'state-of-the-art' experts", but according to whether the material is published in respectful peer-reviewed journals, endorsed by other researchers in the field, and notable enough. These were the reasons that I removed your suggested contribution. Thanks for removing the other piece of text - I agree. Yevgeny Kats 03:19, 31 March 2007 (UTC)

Why did Ancheta revert the last edit of 213.58.99.45 without even giving a reason, especially after the user explained himself in the Talk page, and another editor (me) joined the discussion and supported the suggestion of 213.58.99.45? The sentence that the user suggested to remove indeed shouldn't be there. It's just a piece of wrong science that doesn't have any notability or impact (no citations at all!). There is no reason that this thing will appear in the article "Gravity". Yevgeny Kats 19:27, 31 March 2007 (UTC)

"this thing" that you attempt to scorn at, here in the public space, describes what you and your peers will find sooner or later, presumably in a hard way, to be the only avenue that can be explored in order that physical world in which we dwell, and its aim, may be understood. I am only sorry that I even brought this untouched virgin Knowledge into here, to be disrespected among such miserable inhuman thinkers drowned in their own intellectual arrogance: "Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet, and turn again and rend you." (Matthew 7:6). Nevertheless, at the same time, none of you Sirs can say anymore that didn't receive a proper word of advice. Yours faithfully.

I apologize if my response sounded impolite. This wasn't my intention. Yevgeny Kats 23:45, 31 March 2007 (UTC)

Anheta Wis will have to answer for himself, but I can tell you that my initial reaction to the anon's second edit was "of course this should be reverted". Then I looked at the reference and quickly realized that he was correct. IMO, the real question is how the insertion of the text the anon deleted had gone undetected. What I have found in that the change appeared on February 5 (see this diff), and was followed another anonymous edit that was reverted. Apparently noone went back to the previous "good" version to see what else had been done by the other anons, and so that edit "stuck". *Sigh*. Let's just say that this is not the first time that I have seen this kind of thing happen. --EMS | Talk 19:47, 31 March 2007 (UTC)

Glad to be of service. --Ancheta Wis 21:45, 31 March 2007 (UTC)

Gravity versus gravitation

The article claims that in scientific terminology the term "gravity" refers to the Newtonian force, while other theories (such as general relativity) should use the term "gravitation". I don't think it's true. For example, a search in Google Scholar gives 276 hits for the expression "Einsteinian gravity", and only 83 hits for "Einsteinian gravitation", which is the opposite trend from what the article claims.

We can also search for "Newtonian gravity" 4320 hits and "Newtonian gravitation" 1320 hits.

As you see, in both cases the word "gravity" is used about 3.3 times more than "gravitation", without any difference whether they refer to Newtonian or Einsteinian theory. Therefore, I suggest removing that section, and just mentioning both terms in the first sentence of the article as synonyms. Yevgeny Kats 01:14, 1 April 2007 (UTC)

Yevgeny - I think that the idea of merging that section into the introduction is a reasonable one. However, the term "Einsteinian gravity/gravitation" is used almost exclusively by those of us who are seeking to distance ourselves from general relativity itself. Given the type of person who usually takes on such a project, I am not surprised to see "Einsteinian gravity" used more than "Einsteinian gravitation".

A little history will also come in handy here. For a long time, that section was this article. That was all that it said, and I guarded it zealously to keep it from being redirected to gravity. I always intended to expand it one day, but never quite got around to it. Suddenly, just over a year ago, Sadi Carnot comes along and rearranges everything related to Newtonian gravity and the development of gravitational theory. That is when this page became the main page related to gravity and gravitation. Realizing that Sadi was aware of my point and running with it farther and faster than I could, I just plain got out to the way but made sure that the section in question did not get lost in the shuffle.

Overall, I have found that most GR researchers prefer to talk about "gravitation" and "gravitational theory". Most textbooks that I have seen refer to GR as a theory of gravitation instead of a theory of gravity. Jim Jast's point that "gravity does not exist" is actually fundamental to relativity theory (in a form called the equivalence principle).

My suugestion is to state that "these terms are often treated as being synonymous, but most researchers in the field of gravitational theory distinguish between the two: ..." . --EMS | Talk 02:53, 1 April 2007 (UTC)

I don't think there is any significant distinction between the words "gravity" and "gravitation" in the scientific community. Could you please show me that such a distinction actually exists? Yevgeny Kats 15:52, 1 April 2007 (UTC)

See Ohanian, Hans C. & Ruffini, Remo (1994). Gravitation and Spacetime (3rd ed.). New York: W. W. Norton. ISBN 0-393-96501-5.{{cite book}}: CS1 maint: multiple names: authors list (link) for one. The authors only mention "gravity" as the "force of gravity". Otherwise they refer only to gravitation. Also, amongst my books, Wald, Robert M. (1984). General Relativity. Chicago: University of Chicago Press. ISBN 0-226-87033-2. only uses the work "gravitation". The same for Bowler, M. G (1976). Gravitation and Relativity. Pergamon Press. ISBN 0-08-020567-4. only uses the word "gravitation". To top it off, I have taken classes in general relativity at the University of Maryland with the professors in its Gravitation group, and they were very definite about this distinction.

I can understand your skepticism. In classical mechanics there is the force of gravity and the law of universal gravitation. So I can see why the two words seem to be used interchangeably. Indeed, the phenomenon and the force are so intertwined that many people don't bother to make the distinction, but I assure you that it is there. Look at it this way: If they are not two separate things, then why bother having two separate words? --EMS | Talk 17:07, 1 April 2007 (UTC)

What you're telling us about is just your personal experience, and I think only a small fraction of scientists think that such a distinction should be made. My experience shows that the words are used interchangably. You didn't like the search results I presented above. Here is another piece of evidence that is completely against the trend you're defending: probably you heard the expressions supergravity, quantum gravity, Kaluza-Klein gravity. All these terms refer to general relativity or its generalizations, not to Newton's force law, and still these expression almost always use the word "gravity" rather than "gravitation". Therefore, I think the paragraph about the distinction between the two terms isn't WP:NPOV and should be removed. Yevgeny Kats 17:48, 1 April 2007 (UTC)

Kaluza-Klein is the only one there which at all contrdicts what I am saying, as the other two are supposing that gravitation is due to an active exchange of gravitons while GR only admits gravitons as the messenger for changes of spacetime curvature. Therefore by the rule given above those are indeed theories of gravity (in that they call for gravitation to be due to a force). Kaluza-Klein was ironically enough an attempt to extend Einstein's paradigm for gravitation to electromagnetism. (In fact I am getting suspiscious that "Kaluza-Klein gravity" may be a different altenate theory inspired by the work of Kaluza and Klein, or it could just be a misnomer. However I will admit that the important thing is that it is there.)

You are right that only a small fraction of scientists will make this distinction, but that fraction is the majority of scientists who deal with general relativity. Please remember that "gravity" really means the "force of gravity". In classical mechanics "gravity", "force of gravity", and "gravitation" are the same thing. However, in general relativity, gravitation is not due to a force, but instead to spacetime curvature. That is when it becomes important to distinguish between the phenomenon and the force, and that is why my experience has called for that distinction to be made.

So a "small fraction" it may be who make that disctinction, but given that it is made by the small fraction who call themseves gravitation researchers, I think that said distinction should be respected here. --EMS | Talk 18:21, 1 April 2007 (UTC)

Zdravstvuy Yevgeny, if an opinion of Jim the troll counts for anything it is that EMS is perfectly right since "gravitation" is a physical phenomenon while "gravity" is a physical force (non existing BTW as a fundamental force) and that's why I didn't like the first sentence of the "gravitation" page. This setence would be OK in a "gravity" page though since a lot of folks think that "gravity" is a "fundamental force of attraction mediated by gravitons" (they see this force, don't they, like some time ago they saw the Sun going around the earth, and even earlier a flat Earth and the Sun born every day since there was no way for the old one to get from the West to the East). All the experimentalists I know think along these lines. They believe only in what they see. Which is good because it prevents them from believing in good or evil spirits. But, IMHO, the GR is here to stay even if experimentalist hope that they don't have to learn it since "soon" it is going to be replaced by "quantum gravity". Eventually they have to change their opinions since the GR is a fact and ignoring facts is as bad a thing as believing in good and evil spirits. BTW, are you a theorist? Jim 13:07, 2 April 2007 (UTC)

Jim - I thank you for your support on this issue, but not for your continued POV pushing. IMO, even under GR gravitation acts as an attraction between masses, and so I will leave that first sentence as-is. (Note that I agree with your reason for wanting to change it even if I don't agree with the change.) As for quantum gravity: It is what it is. I also roll my eyes at it, but who am I to complain about someone reseaching an alternative to general relativity? Also, please realize that GR is a theory, not a "fact". The fact is that GR is well accepted due to its being confirmed by observation. --EMS | Talk 14:24, 2 April 2007 (UTC)

EMS - This is what I meant since "facts" are only just results of observations until they are proven wrong by a different theory which interprets those observations differently. "Facts" aren't absolute since "without a theory one can't understand the observations" [Einstein]. E.g. the Sun running around the Earth was once a "fact" but not anymore. So the experimentalist (especially Feynman) have also their point but it becomes valid only when they understand the theory and not when they want to skip GR as "too difficult" (let's better stick to Newton with "corrections") or as "not agreeing with QM" (let's make a brand new theory of "quantum gravity" and forget about curved spacetime). Jim 15:35, 2 April 2007 (UTC)

I disagree with those who would want to diminish the distinctions between gravity and gravitation. Please consider the following; in current thinking, when light from a distant star is “bent” (in Euclidean space) as it goes past a massive object, it is in fact going along a “straight” line (in curved space-time) known as a geodesic (which minimizes the “distance” that it travels). According to the general theory of relativity, to say that the light was “attracted” toward the massive object is incorrect. If the light had gone straight in Euclidean space or in any way not followed the geodesic as it passed this massive object, then we could say that it had been attracted and accelerated toward something. Similarly, for the article to say "“Gravitation" is the attractive influence that all objects exert on each other, while "gravity" specifically refers to a force which all massive objects (objects with mass) are theorized to exert on each other to cause gravitation.” rips out and throws away the heart and the central premise of the general theory of relativity which as a theory of gravitation states that there is no force of gravity and that there is no attraction (or acceleration) of bodies due to this force. AikBkj 15:43, 8 November 2007 (UTC)

Early Indian gravitational theory

Jagged 85 (talk · contribs) edited the start of the "Early history" section to read:

Since ancient times, there have been many attempts to understand and explain gravity. From the 8th century BCE, philosophers in ancient India may have understood that a form of gravitation held the solar system together. <ref>Dick Teresi (2002), Lost Discoveries: The Ancient Roots of Modern Science - from the Babylonians to the Maya, Simon & Schuster, New York, ISBN 0-684-83718-8:

"Two hundred years before Pythagoras, philosophers in northern India had understood that gravitation held the solar system together, and that therefore the sun, the most massive object, had to be at its centre."

</ref> In the 4th century BCE, Greek philosopher Aristotle believed that there was no effect without a cause, and therefore no motion without a force. He hypothesized that everything tried to move towards its proper place in the crystalline spheres of the heavens, and that physical bodies fell toward the center of the Earth in proportion to their weight.

I find this to be an amazing assertion, especially the indication that it was known that the Sun is much more massive than the Earth. Most ancient cultures thought that the Sun was small as compared to the Earth. Even with a heliocentric theory (and the resultant realization that the Sun must be bigger in order to function as the central mass), I see no evidence of a gravitational theory here, but instead a blanket statement that an influence exists. In any case, more and more scolarly documentation is needed of this business. --EMS | Talk 03:10, 12 May 2007 (UTC)

I've added another quote from an ancient Indian philosopher around that time who tried to explain gravity. I really don't see what's so amazing about this though. It's really not that hard to come up with a gravitational theory of some kind. I wouldn't be surprised if the Egyptians and Babylonians made earlier attempts aswell. As for the heliocentric theory, that's a different issue altogether and doesn't really need to be discussed here, but it just happens to be part of the quote. Jagged 85 05:57, 15 May 2007 (UTC)

Merge needed

Hi, I stubled upon this stray article: Gravity (fundamental forces); will someone please merge this article into this one. Thanks: --Sadi Carnot 16:43, 12 May 2007 (UTC)

I find it odd that you are calliong this article "stray" as you created it! In any case, I have merged in the one thing that I thought was worthwhile, and will now ~~initiate an AfD on~~ "prod" it. --EMS | Talk 17:13, 12 May 2007 (UTC)

Intelligent design of gravity.

As a supposed "fundy", I will furious to read this in my email inbox. According to a recent artilce online there is strong evidence that while scientists cannot explain why gravity works, the Evangelical Center for Faith-Based Reasoning has concluded that there is a "higher power" controlling what we understand as gravity. I am curious as to why Intelligent Falling (ie God wants things to fall) is not given proper discussion in Wikipedia. Website: (http://www.theonion.com/content/node/39512) Respectfully, Grandadd 03:27, 23 May 2007 (UTC)grandadd

Nice reference. The Onion is a well-known humor rag founded in Madison, Wisconsin, currently with editorial offices in Manhattan. Some of their work includes Our Dumb Century, with appropriate tongue-in-cheek commentary in the weekly paper about this encyclopedia. --Ancheta Wis 03:49, 23 May 2007 (UTC)

Simplification of Newton's law of gravitation

According to this article, "Newton’s law of gravitation simplifies to F = ma". While the F in in the law of gravitation can obviously be usefully equated with the F in F = ma, I do not see how the former equation can be said to "simplify" to the latter. Can anyone clarify what this statement is supposed to mean? Matt 00:32, 10 June 2007 (UTC)

At one time the article said 'simplifies to F = mg', where m and g are scalars, with g = constant 9.8m/sec/sec. This is Galileo's finding and the basis for the law of falling bodies. --Ancheta Wis 01:20, 11 June 2007 (UTC)

I don't understand what you're getting at - whether it's written F = mg or F = ma makes no odds. The equation F = ma applies universally. It would (or could) still apply even if gravity didn't obey Newton's inverse-square law. The law of gravitation is a completely different concept. It explains how the force of gravity arises from the masses and distances involved. You cannot get from the law of gravitation to F = ma, or vice versa, just by a process of "simplification". They are, as far as I can see, two completely different things, that can be combined to work out the acceleration of a falling body, say. That's quite different from "simplification". Matt 11:14, 11 June 2007 (UTC).

I rephrased it. Two different laws say F = mg and F = ma, from which we can conclude a = g. --Patrick 11:42, 11 June 2007 (UTC)

We're talking at cross-purposes here. I was not quibbling about whether it should be "a" or "g", I was questioning the word "simplify". However, having just read this paragraph again it makes perfect sense - it's just saying that when "r" in the law of gravitation is constant, the formula F = m1*m2*G/r^2 becomes F = m1*g for some suitable constant g. I understood this perfectly well all along, so I really don't know what was confusing me. Brain clearly not engaged! Thanks anyway, and btw I have just tweaked the formatting there. Matt 23:41, 11 June 2007 (UTC)

WHY do objects exert force on one another? Is this field completely understood, or is it a mystery?

Please forgive me if this was adressed in the article, but I couldn't find a specific enough answer within the body of the article.

Why, exactly, does gravity exist? Everyone knows that an object of sufficient enough mass (a planet for instance) will exert a pull on other objects, but why is this? What is it about mass that creates a force? The force of gravity seems to come from nowhere.

Is this "just the way things are" or is there a specific scientific explanation for why mass causes gravity? EvaXephon 03:30, 11 June 2007 (UTC)

It's a profound question. Not even Newton could answer it. All he could give was what. The mechanism of gravitation (the how of gravitation) is current research. The Higgs field is a potential answer for the origin of mass. But that only answers how. So we might invert this and say that Newton was smart enough to know he couldn't answer why. Perhaps in another 400 years, after another Newton develops. --Ancheta Wis 10:44, 11 June 2007 (UTC)

Very encompassing and informative! Thanks for your time. EvaXephon 10:05, 12 June 2007 (UTC)

You're asking the chicken/egg question. However, let's go with James Clerk Maxwell who wrote in the 9th edition of the Ency. Brit. that no one has ever seen a force and as far as I know he's still right. What you do like Galileo and Newton is note the actions of real physical entities and develope causitive concepts and rules of behavior from those observations.WFPMWFPM (talk) 02:13, 10 June 2008 (UTC)

Newton was wrong edit

I noticed at the bottom of the article someone posted a thing about his theory of gravity, which to mean seemed a very stupid theory trying to say magnetism has the same properties as gravity, but anyway thats not the point - should it even be there? It was just posted today according to the history.

Sicewa 20:02, 16 July 2007 (UTC)Sicewa

johnny 1/8/07

please help

sorry to but in but i have many questions which may seem very simple to you guys what keeps a neutron spinning does the neutron leave a void in the space it has just left + could it pull another atom towards it do neutrons show any syncrinisation to each other when together first time on wiki no idea if this is what it is for or how to spell cheers johnny fabioyiuopouuuuuuuuuuuu 09/908/088 —Preceding unsigned comment added by 69.15.65.50 (talk) 21:02, 7 February 2008 (UTC) You have asked a great question and aren't going to get many answers. However let's say there are a lot of small particles (gravitons) that are being attracted by gravity into a very small volume of space. but they cant get together because their line of motion isn't aimed at the central point of attraction. So then they kind of mix with each other and acquire a more or less uniform property of angular motion around the central point. Then maybe the central particles of this "particle cloud" manage to "cohere" or achieve fixed positions relative to each other and then grow in size to some volume restriction limit. That moght do for a stert.WFPMWFPM (talk) 17:33, 11 June 2008 (UTC)

Spin & Gravity

I've encountered online several people who believe that gravity is caused by spinning. They think that if the Earth stopped rotating, gravity will stop and everything will start floating into space. I have pointed out a least one web site that disputes this idea, but they seem set on ways of thinking. —Preceding unsigned comment added by 63.164.202.130 (talk) 15:32, 11 September 2007 (UTC)

Calculating end of solar system

Since the total mass of the sun is known (1.9891 ×10³⁰ kg or 332,946 Earths), 99.86% of the Solar System's total, wouldn't it then be possible to calculate were the gravitational influence of the sun ends, in other words: at what distance would an object no longer be pulled into an orbit around the sun? Currently, the edge of our solar system is only estimated to end at the Oort cloud, at a distance of about 50,000 AU from the Sun (1000 times the distance from the Sun to Pluto or nearly a light year). Why isn't a precise calculation made yet, if possible?

I'm far from an expert on the subject, but I saw a pretty cool picture the other day on Wikipedia, but couldn't remember where. I think it might have had something to do with the Voyager or Pioneer Probes. It showed the borders of various things such as the Oort Cloud and the Termination Shock and the Heliosphere and such.

Opinions on what constitutes the boundary of the Solar system is certainly one problem. Perhaps, like the boundary between the Earth's Atmosphere and Space, there really isn't one. My own opinion is that all objects in the universe exert some influence on all other objects depending on their Gravitational Mass and distance. If that were the case, then there would be no true border, only a point where its influence became infinitesimally negligible. Hopefully someone better informed will be able to give you a more satisfactory answer. --Demonesque 04:49, 2 September 2007 (UTC)

I'm familiar with the Termination Shock and that image. But as I stated, I want to calculate the endpoint of the Sun's gravitational pull, not were the solor wind ends, it's two different things. A mass can cause gravity to bend the space fabric, see this picture from the earth for example: http://science.nasa.gov/headlines/y2005/images/gpb/vortex1_crop.jpg

Now at the end of the "gravity well", were the line is horizonzal, an object is not catched by the earth. But when it enters the well, it will start to orbit the earth as it's moon. The same applies for the Sun. So my question is: were ends the "gravity well" of the sun, it is calculatable? Please take a look at this movie from NOVA (The Elegant Universe 3/8, you need Quicktime): http://www.pbs.org/wgbh/nova/elegant/media2/3012_q_03.html --Patrick1982 18:33, 2 September 2007 (UTC)

Okay for anyone still interested, I found an answer. It is related to the Inverse-square law; see here: [4]

at 340km heigth, the International Space Station experiences only 90.13% of Earth's gravitational pull (6378,137^2 / 340^2 *1 *100 = 90.13%). So at 20 million kilometers away from earth, the pull is only 0,00001%. However the line goes very slowly to 0% (actually it never reaches 0% and goes on to infinity!). At Mars, 78 million km from Earth, the pull will still be 0,00000067% so the two planets effect each other's orbits at verry low levels! Now going back to the Sun, the calculation is as follows when observing the distance of Pluto: 695000^2 / 5906376272^2 *27,94 *100 = 0,0000014%. So this number appears verry weak, but still it is enough to get Pluto to orbit around the Sun! The Oord-cloud starts at 20,000 AU, so the calculated pull is 0,000000000005%. Furthermore, even at the nearest star, Proxima centauri, the Sun still has a gravitational pull of 0,00000000000003%! Only now I can see the problems of my underlying question: n-body problem. --Patrick1982 20:41, 26 September 2007 (UTC)

Gravitational Distribution

Just thought I'd bring attention to some apparent pseudoscience. A new page has been created entitled Gravitational distribution. I think it should be deleted. The supposed effect is not explained in any reasonable way. The author him/herself admits that it hasn't been verified, and has no equations to describe the effect. I deleted some stuff the same author added to this article. Someone other than an IP want to take care of the deletion of the other article? --131.215.123.98 18:38, 4 November 2007 (UTC)

Use one of the templates from WP:CSD. I think it won't survive :-) DVdm 18:56, 4 November 2007 (UTC)

It's not obvious to me that this qualifies for speedy deletion. It's clearly not vandalism. Also, while WP:CSD does mention patent nonsense, it specifically says that doesn't include implausible theories. In any case, I edit anonymously because I don't want to be drawn into these behind-the-scenes struggles. I just want to bring it to the attention of people who can stomach these fights. (I know that's a wimpy cop-out, but it's a decision I've made. Sorry.) --131.215.123.98 19:16, 4 November 2007 (UTC)

P.S. It looks like User:Glacialvortex is back at it, though claiming to have sources. Like I say, I don't want to get drawn in... --131.215.123.98 19:19, 4 November 2007 (UTC)

I have added the tag. I will revert the new attempt on this article. DVdm 19:25, 4 November 2007 (UTC)

Thanks. --131.215.123.98 19:35, 4 November 2007 (UTC)

The author placed a {{hangon}} tag and wrote on the talk page of the article that he was the creator of the theory. After a quick look at a few relevant passages I pointed to on WP:NOR, the author understood about Wiki policy and was comfortable with the idea that the article should be deleted. By the time I could say thanks and good luck, the article and its talk page were already deleted. Cheers, DVdm 20:21, 4 November 2007 (UTC)

Very nice work! Well done. --131.215.123.98 20:52, 4 November 2007 (UTC)

Gravitation is the Reason (?)

I find the sentence in the introduction "Gravitation is also the reason for the very existence of the Earth, the Sun, and most microscopic objects in the universe; without it, matter would not have coalesced into these large masses and life, as we know it, would not exist." somewhat (not a lot) philosophical and dogmatic. Anyways, my view would be that matter is infinitely more a reason for the very existence of the Earth, the Sun, etc... and that gravitation plays an important but secondary role. Maybe I am reading too much into the sentence. I think it is the “very existence” and the “life … would not exist” parts that get me. I will admit to a bias that I have; I feel a twinge whenever scientific thought, effort and knowledge is presented as we absolutely (or for that matter, even remotely) know what happened and how the world works as opposed to our best understanding to date is ... Along the same lines, I do not subscribe to the infallibility of science, scientific theory, and um, scientists (which would include myself). Irrespective my flaws and bias, I think that the article would be improved if the coalescence of matter and the formation of the Earth, planets, Sun and other macroscopic objects would be added to the existing previous sentence which already lists the things for which (we currently understand) gravitation is (in part) responsible. AikBkj 17:06, 9 November 2007 (UTC) On the contrary, gravity would have destroyed the earth by making it part of the sun except for the fortuitous circumstance that the mass of the earth managed somehow to retain half of its lost potential energy with respect to the sun's gravitational field and convert that to an orbital velocity around the sun. And dont ask me how.WFPMWFPM (talk) 02:40, 10 June 2008 (UTC)WFPMWFPM (talk) 02:43, 10 June 2008 (UTC)

Between 8.4 and 10.6 m/s^2?

The article claims that "[the] value [of the strength of the gravitation field] at the Earth's surface, denoted g, is between 8.4 and 10.6 m/s²". I don't think that on the Earth's surface there is any place where it is that strong or that weak. In the Earth's gravity article, there are values in some cities, ranging from 9.779 m/s^2 in Mexico City to 9.819 in Helsinki and Oslo. On some high mountain near the Equator it'll be even less, and at the North Pole it'll be even more, but definitely not as much/less as 10.6 or 8.4. --Army1987 11:06, 11 November 2007 (UTC)

Yea, something odd there. In the article on Earth's gravity in the section on Altitude, I noticed this "In reality, the gravitational field peaks within the Earth at the core-mantle boundary where it has a value of 10.7 m/s², because of the marked increase in density at that boundary." Maybe that's where one of those numbers came from? The core starts at a depth of about 2890 km according to the article on Earth, not exactly part of the Earth's surface. AikBkj 15:13, 11 November 2007 (UTC)

Falling Objects and Rates of Acceleration:

I didn't see in the article that this point was brought up, but should it be mentioned that heavier objects do in fact fall more quickly than lighter objects?

I can understand the reasoning behind teaching to people who are new to the subject that objects fall at the same rate and will hit the ground at the same time when dropped from the same height. But, being an encyclopedia article, should it not be explained that this is actually a misconception? Just for technical accuracy, I mean. It's not really important for the average person to know this, but for those who choose to study gravity in further detail, the teaching that all objects fall to Earth at the same rate regardless of their masses introduces an early misunderstanding that, though such a belief is acceptable for most practical applications, it is actually contrary to the way gravity actually works. -=( Alexis (talk) 17:42, 24 November 2007 (UTC) )=-

Please do not post that statement to the article. An astronaut conducted this experiment on the moon. Galileo's experiment holds; Aristotle was wrong and Galileo noted this in 1638. Air resistance will alter the rate of fall but the dependence on air was one of the factors that Galileo accounted for. If you have questions, you are welcome to google "Apollo astronaut feather experiment" .--Ancheta Wis (talk) 18:06, 24 November 2007 (UTC)

Here is a video of the Apollo 15 experiment performed by Astronaut David Scott on the moon. The video demonstrates that the dropped feather and hammer hit the moon at the same time. --Ancheta Wis (talk) 18:42, 24 November 2007 (UTC)

When you say that larger objects fall more quickly are you referring to the fact that the Earth is pulled ever so slightly more to the larger object? I do not believe this is worth mentioning as that difference is immeasurable. It would be confusing at best, misleading at worst. Ben Hocking ^{(talk|contribs)} 17:59, 24 November 2007 (UTC)

The concept of relative displacement (both objects move) is discussed in the last few sentences in the section "Earth's gravity”. Also, Newton's law of universal gravitation is wikilinked in the section directly following the section on “Scientific revolution” (which mentions air resistance) for those who wish to learn more detail. The existing text would seem to address the concerns of Alexis from what I understand.

By the way, for technical accuracy, if one (like Galileo) drops two objects of different masses, they will hit the ground closer to the same time than Alexis might think (ignoring air resistance, etc). Consider that the absolute acceleration and absolute displacement of the Earth will be identical for both (since the drops are occurring simultaneously). The Earth’s motion would be very slightly different only if the drops are done separately and timed. I would agree with Ben’s assessment that this type of detail in the article would be misleading considering the other effects which become important at this level. AikBkj (talk) 16:32, 28 November 2007 (UTC)

     What would happen if you dropped 2 objects, both being the exact same size and shape, but one weight 1 pound on the moon, and the other weighed 10 pounds with no air resistance, then dropped both at the exact same time at the exact same height on exactly leveled ground? I am pretty certain that the 10 pound object will hit the ground first, but I also know that the difference in time will be really short.
     I have been thinking about this since I came across something I did not like on a game that I was playing and have been thinking since... My question to myself was, "If someone could jump 100 feet into the air, should that person be able to land the fall without taking any damage? (This is not putting into consideration on how that person lands, or how their internal organs and such move around)... I was trying to find the formula to see how much force would be required from the initial jump as well as the ending impact. I mean, how much force would somebody need to use in order to jump that high to begin with?
     If anybody wants, email me at Szayn_Zaniir@hotmail.com Szayn (talk) 22:54, 8 December 2007 (UTC) —Preceding unsigned comment added by Szayn (talk • contribs) 22:50, 8 December 2007 (UTC)

See the video of the Apollo 15 experiment performed by Astronaut David Scott on the moon. This experiment on the moon showed that the feather and the hammer land at the same time. Galileo predicted this in 1638. Ancheta Wis (talk) 23:35, 8 December 2007 (UTC)

If you did fall from 30.48 metres (100 feet) from the surface of the moon, after 6.13 seconds of falling you would hit the ground at 9.9 m/s (22 miles per hour). This is the same as falling from 5 metres (16.5 feet) on Earth in terms of the speed at which that you would hit the ground. It is highly likely that you would survive this jump, although you could twist or even break something. People with more mass are more likely to be injured. I'm not an expert on human durability, but if you don't weigh too much, don't have any joint problems, and know the best way to land you should be able to land without taking damage. By the way, the high jump world record holder Javier Sotomayor would only be able to jump about 15 metres (50 feet) on the moon. The force required to jump a certain distance is dependant upon the weight of the person jumping. You should be able to jump a little more than six times the height you can jump on Earth as long as you aren't burdened by a heavy oxygen tank or space suit. Out of curiosity, what game are you referring to? Jecowa (talk) 14:22, 19 December 2007 (UTC)

Contradiction

This article says:

"In scientific usage gravitation and gravity are distinct. "Gravitation" is the attractive influence that all objects exert on each other, while "gravity" specifically refers to a force which all massive objects (objects with mass) are theorized to exert on each other to cause gravitation. Although these terms are interchangeable in everyday use, in theories other than Newton's, gravitation is caused by factors other than gravity. For example in general relativity, gravitation is due to spacetime curvatures which causes inertially moving objects to tend to accelerate towards each other."

However, the Fundamental interaction article implies throughout that in general relativity gravitation is a force, and in at least two places it explicitly says so:

"Gravitation is by far the weakest interaction, but at long distances is the most important force."

"Thus large celestial bodies such as planets, stars and galaxies dominantly feel gravitational forces"

Something needs fixing here. Matt 14:43, 3 December 2007 (UTC).

The problem is with points of view. What Newton and Galileo viewed as an influence due to force is due to the geometrical curvature of a 'trajectory' (called a geodesic) in Einstein's view. So the sentences might be reframed

"Gravitation is by far the weakest interaction, but at long distances gravitation is the most important factor (in the motion of objects). Thus large celestial bodies such as planets, stars and galaxies dominantly feel gravitation (rather than the strong, weak or electromagnetic forces)."

You are touching on an important point, which is about inertia and how it is defined with respect to a reference frame. For Galileo, 'rest' was obvious, but how do you assert what that means for galaxies, galactic clusters or even larger contexts? --Ancheta Wis (talk) 23:48, 8 December 2007 (UTC)

This point relates to a fundamental difference between how gravity is viewed in general relativity (where gravity is not viewed as a force), and how it is viewed in quantum mechanics (where it is, although a force so weak that it's almost always ignored).

However, the statement seems to be proposing a distinction in terminology that is not commonly used by actual physicists. This statement "in theories other than Newton's, gravitation is caused by factors other than gravity" really does not reflect the way that the term is used by physicists, or by anybody else. It's just not the way the term is used, and I will see if I can rewrite the section to reflect this. Geoffrey.landis (talk) 03:46, 14 December 2007 (UTC)

OK, so we seem to have established that in GR gravity/gravitation definitely isn't a force. So, in addition to the clarifications you have made to this article about the meaning of the terms "gravity" and "gravitation", should the Fundamental interactions article also be tweaked to make this clearer? That article states at the start that GR is the "current theory" of gravitation, and the implication is that the statements made there about gravitation pertain to the GR viewpoint. So, am I right in thinking that it shouldn't be referred to there as a force -- or there should at least be some caveats? Matt 01:30, 16 December 2007 (UTC).

I wish there were a simple answer to this query. At one level, it's a question of definitions more than a question of real physics: a question of what you chose to define as a force. In General Relativity, it's convenient in many cases to just pick a freely-falling reference frame, and in that frame the "force" of gravity doesn't exist by definition, and since the GR theory has built into it the techniques to transform into any reference frame, this is straightforward. You can formulate GR in such a way as to treat gravity as a force-- this is perfectly acceptable, but has the conceptual disadvantage that it ends up with frame-dependent descriptions, which true relativists disdain as inelegant. In quantum mechanics, though, it's more convenient to deal with gravity, if you ever need to, as a force fundamentally no different than any other. Certainly in classical mechanics it's straightforward to think of gravity as a force. (Real physics tends to deal in potentials rather than forces at a fundamental level anyway-- in fact, Mermin argued in Physics Today that we shouldn't even teach F=ma anyway, we should just go right to potentials).

Overall, I think that any "clarification" would probably end up muddying things and end up being more confusing than explanatory. Geoffrey.landis (talk) 02:26, 16 December 2007 (UTC)

Unit examples?

Would be nice to include comparable graviation forces on our closest planets, and an example of what the actual difference recorded in gravity with height and negative height. —Preceding unsigned comment added by Seb-Gibbs (talk • contribs) 16:23, 21 December 2007 (UTC)

That was formerly on this page but was put on a child page to save space. Comparative gravities of_the Earth Sun Moon and planets can be found here --Ancheta Wis (talk) 18:58, 21 December 2007 (UTC)

What about Einstein?

There is a nice sentence in the main article (between other nice sentences):

Modern physics describes gravitation using the general theory of relativity, but the much simpler Newton's law of universal gravitation provides an excellent approximation in most cases.

While it is true that Newton's law is much simpler and sufficient in most cases because it does not require to understand how the gravitational force is generated but a bad part of it is that being simpler it's not true (for the lack of attractive force acting through vacuum). So why wikipedians keep around this sentence instead of explaining how the modern physics explains the gravitational force? Would the wikipedians didn't know how and would my professor be right maintaining that the physics students are too stupid to understand spacetime curvature (when I proposed to him to teach gravitation at the first year of physics instead of waiting till post gradute studies)? Jim (talk) 23:56, 21 December 2007 (UTC)

And the effect of gravitation on the atomic clocks of the satellites in the global positioning system is non-neglible as well, so we can't ignore Einstein in our daily Newtonian lives either. --Ancheta Wis (talk) 00:57, 22 December 2007 (UTC)

We not only can ignore Einstein but we do. The wikipedia editors revert any attempt to explain the Einsteinian gravitation to high school students. The result is that virtually no physicist, who usually learns the gravitation at high school, knows the simple Einsteinian derivation of gravitational force and how it follows from curvature of space and time dilation. Or even heard about it. After more than 100 years after of Einteinian gravitation. Jim (talk) 04:10, 22 December 2007 (UTC)

I'd say that physics is not about "being true", but about "being useful" and about providing tools to describe rather than to explain. Newton's law of gravitation is neither true, nor untrue. It is useful, simple, and it works - in most cases. That is a fact and i.m.o. not really open for debate.

I think that the nice sentence is sufficient - at least for the average high school student. DVdm (talk) 11:07, 22 December 2007 (UTC)

The point of view is called pragmatism. Unfortunately, the founders of the science would not have discovered what they did from pragmatism alone. They were driven by passion: Galileo, Newton, Einstein. They spent years of their lives on this and we reap the benefit, but it does disjustice to physics and physicists not to acknowledge their motivation, which transcends being useful. Physics is true and useful. --Ancheta Wis (talk) 15:07, 22 December 2007 (UTC)

I propose to baptise this point of view scientific passionism, but I don't really see its relevance in the context of Jim's question. DVdm (talk) 15:59, 22 December 2007 (UTC)

Physicists call "physics" only what is true. Otherwise it is called "math" or "magic". Good physics has to follow the truth verifying it through observations and experiments. Good math has to follow logic working with assumptions. The truth doesn't apply to it, only to its assumptions. The magic needs to follow neither the truth nor the logic just the prejudice. That's why 300 years of physics gave more than 3,000 years of math and 30,000 yeas of magic. And that's why disriminating against Einstein's physics by universities and wikipedia is silly even if it's good to professors and editors. Jim (talk) 21:21, 22 December 2007 (UTC)

Conflict between GR and QM

The section originally had this line: "Several decades after the discovery of general relativity it was realized that general relativity cannot be the complete theory of gravity because it is incompatible with quantum mechanics". This statement implicitly promotes a point of view: the correct statement is that GR and quantum mechanics are incompatible, and hence either GR is an incomplete theory, or quantum mechanics is. (or both, of course). It's quite plausible that it may be possible to reformulate QM in a way to incorporate highly-curves spacetime, and that doing so would solve the problem with no changes in GR. I rewrote this section slightly to remove the implied statement that, of the two theories, the one that's in errror is GR, not QM. I'm also not at all sure that the formulation of gravity as a force involving virtual exchange of spin-2 gravitons postdates the (rather slow) realization that QM and GR are incompatible at the fundamental level; in fact, without formulating GR in terms of quantum field theory, you can't really show that GR and QM are incompatible, so I removed a handful of words suggesting this timeline.Geoffrey.landis (talk) 16:06, 4 January 2008 (UTC)

Re new gravity model

Looks like this might be worth reading and mentioning in article:

"In a paper in the August 3 online edition of the Institute of Physics' peer-reviewed Journal of Cosmology and Astroparticle Physics, they put forth the idea that scientists were forced to propose the existence of dark energy and dark matter because they were, and still are, working with incorrect gravitational theory.
The group suggests an alternative theory of gravity in which dark energy and dark matter are effects – illusions, in a sense – created by the curvature of spacetime (the bending of space and time caused by extremely massive objects, like galaxies). Their theory does not require the existence of dark energy and dark matter.
“Our proposal implies that the 'correct' theory of gravity may be one based solely on directly observed astronomical data,” said lead author Salvatore Capozziello, a theoretical physicist at the University of Naples, to PhysOrg.com."

Dark Energy and Dark Matter – The Results of Flawed Physics? By Laura Mgrdichian, Copyright 2006 PhysOrg.com Discussion of J. Cosmol. Astropart. Phys. 08 (2006) 001.
http://www.physorg.com/news77190620.html

-- Writtenonsand (talk) 21:40, 31 January 2008 (UTC)

Pioneer anomaly

I think that this article [5] is about the Pioneer anomaly. Given the source (The Economist), I thought it could be discussed here since it's obviously gaining notability. --Childhood's End (talk) 21:27, 7 March 2008 (UTC)

Gravitation template

Could someone please explain why the gravitation template should be removed? So far two editors seem to have expressed a desire to remove it, although I do not see any particular reason for it. Silly rabbit (talk) 14:30, 8 March 2008 (UTC)

The last editor to delete it explained: "this is a general public article", presumably suggesting that it was a bit complicated to be the lead picture. Would it be more acceptable to bring it back opposite the text to which it refers: Gravitation#Newton's theory of gravitation? --Old Moonraker (talk) 14:54, 8 March 2008 (UTC)

That's a good idea. I also had another thought. Now that the template is gone (or at least moved), someone should find a suitable image to go alongside the first paragraph text. Initially I thought about using the solar system image which is already in the article, but it's a bit oversized. There are loads of nice images which could go here. I looked over at black hole for something very dramatic, although such images may not be appropriate. Silly rabbit (talk) 14:57, 8 March 2008 (UTC)

Regarding gravitational space-time bending

How does gravity effect space time when there is nothing ( or near nothing ( vacuum )) in that space-time?

When looking at gravitational effects specifically when applied to light travelling from distant stars can we be deceived that gravity is constant?

Does a gravitational field only exist when there is mass in that field, or does its gravitational well exist when there is no matter there? To take this a step further would it be possible that a gravitational field with respects to space time bending if it has no mass near it?

Is there an easy experiment to prove this wrong? ---- (Tommac2|Tommac2)

Please keep in mind that this is not the appropriate place to ask questions such as this. This is for discussion of the article itself. To answer you very briefly - gravity is not bending things in space-time but rather bending space-time itself. I recommend reading up on the subject in some introductory texts before going much further. PhySusie (talk) 15:25, 26 March 2008 (UTC)

Gravity vs. Viscosity

I would propose that gravity shares many of the same characteristics as a superfluid. [6] —Preceding unsigned comment added by Rdailey1 (talk • contribs) 16:44, 1 April 2008 (UTC)

I believe that your idea has merit. I have been developing a hypothesis based on an idea similar to this, but because of time constraints I haven't been left the time to develop the mathematics that would be required to back such a strong claim. Stating this has many implications, such that G is not constant and similar things. Unfortunately research of this type doesn't belong on Wikipedia (see WP:OR) but would be more fit for a forum on similar topics. Infonation101 (talk) 04:53, 11 April 2008 (UTC)

Additional research

What about the experiments on gravity done by Milhouse Van Houten? —Preceding unsigned comment added by 68.164.89.236 (talk) 05:57, 10 April 2008 (UTC)

early history

Quote: "According to Kanada, founder of the Vaisheshika school".

Comment: The link to Kanada is not the right one.

Suggestion: Remove the link.

Quote: "it would be Isaac Newton that gave the first correct description of gravity".

Comment: Galileo's description is correct for phenomena close to the surface of the earth where the acceleration of gravity is constant, just as Newton's description is correct for phenomena at low velocities and weak gravitational fields where the general relativistic corrections are small, and Einstein's description is correct at low energies when quantum phenomena are not important.

Suggestion: Remove the remark.

Bo Jacoby (talk) 08:52, 27 April 2008 (UTC).

Round earth

It should be said in the beginning that gravitation is the reason why the earth is round. Bo Jacoby (talk) 08:14, 27 April 2008 (UTC)

It's 3 dimensional space that makes the earth round. In one dimensional space the earth would be a straight line.WFPMWFPM (talk) 12:08, 10 June 2008 (UTC)

A counterfactual assumption! Still, asteroids having weak gravitation are not round. Bo Jacoby (talk) 22:30, 10 June 2008 (UTC).

They would be if they were fluid enough.WFPMWFPM (talk) 17:44, 11 June 2008 (UTC)

Another conterfactual assumption. But confirming that gravity is the force that makes the planets round. Bo Jacoby (talk) 19:10, 12 June 2008 (UTC).

Should this article be in the "fictitious forces" category ?

For information: There is a thread on Talk:Fictitious force asking whether this article should be in the category "fictitious forces". --PeR (talk) 13:17, 15 May 2008 (UTC)

Gravity is Weak

Gravity is weaker than the strong nuclear force, weak nuclear force and electromagnetic force. Why is this not mentioned in the article? There are some very interesting theories on where the energy of gravity goes to, such as other membranes. Altonbr (talk) 13:19, 9 June 2008 (UTC)

Is Gravity a Property of Space, or a Property of Matter?

I'm not much of a math wizard, so I'll ask this question in more mechanical terms. Let's say, hypothetically, if someone could hollow out a room at the very center of the Earth, would he be pulled to the center of its mass, (ie: float in the middle), or would he be pulled toward the mass itself, (be able to walk across all the walls)? 216.67.92.66 (talk) 17:36, 11 June 2008 (UTC) CLewis Yep! Just like in the orbiting space laboratory.WFPMWFPM (talk) 17:48, 11 June 2008 (UTC)

OK, assuming that you answered yes to the first part of my question, gravity is a property of space, I would float in the center of this hypothetical "room" at the center of the Earth. But, unlike the spacestation, because of the Earth's vastly larger mass than my own, it seems to me that I would still be experiencing weight, (in way that would feel more like pressure than weight as we normally experience it). I would be stuck fast at the center, and if someone were to lower a ladder to me, my weight would be a great deal more than it is on the surface. Would this be correct? —Preceding unsigned comment added by 216.67.92.66 (talk) 19:35, 11 June 2008 (UTC) When you say center of the earth I assume you mean the gravitational center, which is where all the gravitational force of the surrounding matter balances out. At that point there would would be no net directional gravitational force and thus no weight.WFPMWFPM (talk) 22:41, 11 June 2008 (UTC)

Gravity is a property of matter moving through space. It arises entirely from the law of conservation of momentum. It exists simply because that's the way matter has moved and will continue to move in accordance with momentum conservation laws. As I see it, there's nothing mysterious about that. As for that "room in the center of the earth", the mass surrounds you from all directions has very little to do with adding to your weight. Much of it will cancel itself and would be far less than what is on the surface.Kmarinas86 ^(6sin8karma) 17:33, 12 June 2008 (UTC)

Kmarinas86, Thank you for the citation. I quote from it "a mass moving at a constant acceleration does not radiate" which is very similar to the situation for charge at constant velocity. It suggests an experiment which must be in the literature: for any astronomical bodies which are rotationally accelerating (and therefore non-constant acceleration), what are the measurements for gravitational radiation? What comes to mind immediately are black holes under increasing rotational acceleration. --Ancheta Wis (talk) 04:35, 5 July 2008 (UTC)

Thank you for these responses. I agree, there does seem to be a direct corrolation between gravity and motion, (namely, accelleration), possibly linked to the speed of light, I don't know.

As the article states, General Relativity says that gravity is caused by curvature in spacetime, which is a hard concept for some of us to wrap our heads around. Teachers often use the analogy of a bowling ball on a trampoline to describe the "gravity well", (as a golf ball set on that trampoline will roll toward it). The section on Newton describes how weight decreases in proportion to an objects movement from the "center about which [the Earth] revolves". By this, it seems to me that my weight would increase the closer I get to the bottom of the gravity well, regardless of the amount of mass above me, and "up" would always be "away from center". That implies to me that gravity is a property of the universe interacting with matter.

The idea that there is a "balancing point", by which at the center I would be pulled equally in all directions, and therefore not pulled at all, tells me that if I were to move slightly off center, an imbalance would be created by which I would be pulled toward the walls of this fictional room. In which case, "up" would no longer be "away from the center", and my weight should actually decrease the deeper I travel into the Earth. Therefore, gravity would be a property of matter interacting with the universe. But I am no expert on the subject. I'm just trying to get a little more of a mechanical explanation, rather than just a mathamatical one. Thanks for the input. 216.67.92.66 (talk) 20:08, 13 June 2008 (UTC) CLewis

Gravity is a property of space-time, not space. Mass (actually energy) creates hills and valleys of space in the 4-dimensional space-time universe that Einstein conceived. The center of Earth is the bottom of one such 'space' valley. As you move from the center of earth you move out of that valley; you start going uphill, or more accurately you start going 'up-space' -- accelerating away from the 'space valley'. In the Newtonian frame, you start feeling a force pulling you towards the center as you move away from the center. To continue in the Newtonian (illusory) frame, as you move away from the center of the earth, there becomes more mass behind you than ahead of you so you start to feel a 'gravitational force' pulling you back towards the center. The further away form the center that you get, the stronger becomes this apparent force because the amount of mass behind you keeps increasing and the mass ahead keeps decreasing. (Looking for references to use for this... anyone else got references for this?) -- Len Raymond (talk) 14:49, 21 June 2008 (UTC)

Thanks, but this view seems to contradict itself. If gravity is caused by "hills and valleys in spacetime", then wouldn't all matter within the Earth's gravitational field only add to that field, in a direction that would cause matter to be pulled to the center with an increasing degree of curvature until reaching the bottom of the well. Then Newton's math should still work, (in reverse of course), all the way to the bottom, which would make the center of the Earth a singularity of such, (no, not a black hole), but in the way that all directions from the center would be up? 216.67.92.66 (talk) 21:31, 21 June 2008 (UTC) CLewis

As I move towards the center, the mass behind me keeps increasing and the mass ahead keeps decreasing. This causes the curvature to get flatter (decrease, not increase). At the center, the curvature becomes completely flat (weightless) -- zero gravity in the Newtonian model. Realize that matter adds in a localized, directional fashion to the gravity field. When you stick a clump of matter to the side of a ball the curvature increases towards the point at which you added the clump, not towards the point at the (old) center of the ball. Important note: Adding this mass actually shifts the center of mass -- towards the added clump -- so the old center-of-mass no longer has zero G's. The old center now has a slight gravity pull towards the new center. Your room analogy has a another issue. To simplify, imagine one inside a hallow ball. In that case, a single piece of loose matter (such as a yourself inside the ball) would, I expect, be 'attracted' to the matter in the wall -- net effect: there is a small gravitational effect towards the nearest wall (towards the nearest matter). But the Earth is not hallow. Any point in the Earth is fully packeted with matter on all sides, all exerting a 'pull'. The net effect: The side of you that is surrounded by the most mass is the side one is 'pulled' towards unless, of course, you are at the center of mass where all sides pull equally. -- Len Raymond (talk) 13:48, 23 June 2008 (UTC)

I'm not sure this is the proper place for a discussion on the subject. I just thought my question seemed rather simple. "Pulled toward center, or pulled toward the mass?" There should be some easy experiments that would show this, (ie: an atomic clock/deep cave experiment, or a drop of mercury in a space at the center of a large lead ball, while free falling). 216.67.92.66 (talk) 21:31, 21 June 2008 (UTC) CLewis

It's a stretch, but this discussion may be useful for the article:

Good exercise on wording for spacetime curvature concepts
Magnet for bringing useful references for this article

-- Len Raymond (talk) 13:48, 23 June 2008 (UTC)

Thank you very much. It never occured to me that way, but that answer makes perfect sense. The bottom of the valley is not a point in space, (as a black hole would be), but a nice "round" basin. I hope this helps other readers understand. As for helping improve the article, all I can say is that the language of math is a very precise language, which can make it very difficult to translate into everyday speech. Thanks again for answering my question. 216.67.92.66 (talk) 16:20, 24 June 2008 (UTC) CLewis

???

There are some people who believe that gravity dose not exist and that there is some logical explanation for the planets to be orbiting the sun and for us to come back down when we jump there is even an explanation for why we even stay on the ground. The planets are able to stay in orbit around the sun because space is like a trampoline pulled tight and you can imagine the planets to be like ants. Now if you were to drop a bowling ball (sun) onto the "trampoline" it would make the "trampoline" have a hole like imprint. Now if the "ants" were to come anywhere near the "bowling ball" they would slide towards it. This is how I believe the planets stay in orbit. For more info check out the book: "The Quantum Zoo: A Tourists Guide To The Never Ending Universe" By: Marcus Chown. When we jump we come back down because the Earth's core is made up of what most people think is hot, molten lava and this lava pushes against the underside of the Earth's surface now when we jump we are in free fall for a small amount of time and since the Earth is blocking our path to continue we land on it. We stay on the Earth's surface because we are pushing against the lava on the inside. This is what causes us to stay on the surface of the Earth. You must remember that this is just a theory and it can be incorrect or correct and the same goes for the theory of gravity existing. Theoretical Physicist (talk) 15:19, 15 July 2008 (UTC)

What you describe sounds like an analogy that is often used to qualitatively describe the relationship between spacetime curvature and orbits in General Relativity. Indeed, in General Relativity, there is no force of gravity -- but gravitation as described in this article does exist, because it's just the term for why massive objects "tend to come together" and has no prejudice about the mechanism. So if you're trying to describe GR, we've got you covered -- and if you're describing something else, then you'll need a reliable source to add it to the article.

By the way, your material was removed earlier because it probably seemed to be a using Wikipedia as a soapbox rather than making suggestions for the article. -- SCZenz (talk) 15:36, 15 July 2008 (UTC)

It was also deleted because you replaced the box at the top of this talk page with your theory rather than putting the comment at the bottom of the page. Besides that, this talk page is for discussing the article, not presenting alternate theories. There are more appropriate places for that. PhySusie (talk) 15:43, 15 July 2008 (UTC)

I agree with -- SCZenz (talk). This is correct with GR. But have you ever wondered if there actually is no such thing as gravity? It sounds kind of weird to have a force that makes us stay on the ground, I wonder if there is a way to prove the theory wrong. Think about it it's the only fundamental force that isn't unified with the other three fundamental forces.

Folks, the purpose of this talk page is to discuss proposed changes to the article, not to propose alternative theories of/to gravity. There are plenty of other forums where you can do that. Can we please close this discussion now. Thanks, Gwernol 17:01, 15 July 2008 (UTC)

Gravity: Energy?

If you pass a magnetic object through a coil you produce an electric current, correct? It is basis of traditional generators. But what if the driving force for said generator was gravity.

Now, hypothetically speaking, if you constructed a coil of truly colossal dimensions and placed it around the earth (or a simmilar body), and then placed in orbit an object with magnetic qualities in such a way that it grew no closer or further from the earth, and said object orbited within the coil, wouldent you have on your hand a generator run purely by gravitation?

If gravity is NOT energy, then this senario defys the conservation of energy, but I cant see why it wouldn't work. If gravity IS a form of energy, then that is one enormous and non poluting souce of power...

Call me a Quack or call me a Genious, I just want to know if this would work.--Hsan007 (talk) 07:46, 16 July 2008 (UTC)

If you drop a magnet through a coil straight down, yes you can get an induced current. You are transferring some of the gravitational potential energy of the magnet into electrical energy. However, there is a problem with the situation you propose. The only reason that an object stays in orbit is that no energy is being lost. There are no resistive forces acting. In the situation you present, the magnet would continually feel resistive magnetic forces as it passes through the coils, causing a relatively rapid decay of orbit. The energy gained by it passing through the coils would not equal the energy it cost to put it in orbit to begin with. So this would not work as an energy source. But it is great that you are thinking about these things - it doesn't hurt to ask. PhySusie (talk) 22:22, 16 July 2008 (UTC)

Besides that - this page is for discussing the article - not presenting ideas. If you have questions like this in the future, feel free to post them at the Science Reference Desk and the people there would be happy to answer your questions.PhySusie (talk) 22:26, 16 July 2008 (UTC)

This is an archive of past discussions about Gravity. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

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Gravity vs Centripetal Force

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Hmm...

Beginning merge & break-up

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Einstein's nationality

Gravity and superconductors

Failed GA

Tesla/Puthoff crank-POV pushing edits

Tesla was right!

The history section is very strange

A bubble with a man in the center of Earth

Gravity and the solar system

Einstein vandal?

header: related?

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aryabhata and gravitation

Proposed changes to section "History of gravitational theory"

Electroweak?

Further reading

Units

First paragraph

Equations for a falling body

Einstein's Jewish Heritage

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Question about gravitation for the article

Existence of Gravity

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POV fork (?)

Inertial Paradox?

Improving "gravitaton" page

Just for the record

Gravity versus gravitation

Early Indian gravitational theory

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Intelligent design of gravity.

Simplification of Newton's law of gravitation

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Spin & Gravity

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Gravitational Distribution

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Falling Objects and Rates of Acceleration:

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Pioneer anomaly

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Regarding gravitational space-time bending

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Round earth

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Gravity is Weak

Is Gravity a Property of Space, or a Property of Matter?

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Gravity: Energy?