Talk:General relativity/Archive 3

The development of GR page has been moved

It is now called the "History of general relativity". That is its topic anyway as a practical matter. Maybe a seperate page on the development phase will be done later. For now, I wish to call a spade a spade. --EMS | Talk 02:55, 12 Jun 2005 (UTC)

Reflections of Relativity link.

On "Reflections on Relativity". MathPages. Retrieved May 29, 2005A., an anonymous user placed in the article:

It is out of date (says black holes are not proven to exist) and errs in saying quantum states are preserved on null geodesics (violates inverse square law of optics). Mixes up photons and other bosons.

First of all, black holes indeed are not proven to exist. The black hole is a theorem of GR, and it is also true that astronomers have found concentrations of matter so massive and dense such that if GR is correct then they must be black holes. However, all observations involving these concentrations of matter are indirect, and many astronomer do not consider it to be a given that these objects are in fact black holes. Many think that these may be quark stars instead, and point to certain observations as evidence of this. Do note that under GR, quark stars only exist for a fraction of a second as a star collapses into a black hole. Stable quark stars, if they exist (and that has not been proven either) would be a serious blow to GR.

Non anonymous, not wrong

It was I who placed the material you find objectionable, and I had signed in. Black holes are proven to exist: There is one at the center of our Galaxy. See recent papers by Schoedel, Genzel, Ekhart and others. There is a movie which with some calculations establishes a massive black hole ar Sag A: [1]

The way the argument runs is that while earlier, people tried to mimic the strong gravity of a black hole by assuming a very dense star cluster or a ball of massive neutrinos, the new observations go in so close that neither of these configurations could be stable. Everybody trying to explain the motions of stars near Sag A* with anything but a black hole gave up about 2 years ago.

The Max Planck page at [2] explains more - two groups UCLA and Max Planck have established the black hole is there. Also look on the web under Fulvio Melia who has given several talks on the analysis and implications.

There are also proven black holes in some X-ray binaries, which can be shown from the flicker period at the inner edge of the disk. Fish a bit on the Web.

--your next complaint-- As for the other comments: I fail to see how quantum states would not be preserved along null geodesics (since they have no passage of proper time). (With the neutrinos, their quantum state apparently not being preserved is evidence that they are massive.) I would also like to see citations of where photons and other bosons are mixed up, as well as for the other criticized portions of that text.

Quantum States - Well maybe I was too sticky there. It seems to me, however, that because the light cone is 3-dimensional, a bundle of rays on it must spread, so its density matrix decreases. That is the inverse square law, which holds classically and in QM. There is also some work showing polarization change in a ray's passing a region of strong gravity, I believe - but hard to look up so if you want, delete that part.

-- the boson challenge--

Bosons: Here is the offending sentence: "In fact, the presence of one boson in a particular quantum state actually enhances the probability of another photon entering that state." from the page: [3]

As to other problems, I am tired of reading that turgid attempt of someone's to put her/his own stamp on relativity. The writer is unidentified, and the discourse ranges from dilatory to heavily laden with equations, often derived in a cumbersome way, with detours.

Pdn 16:07, 16 Jun 2005 (UTC)

Once that data is provided, a decision can be made as to whether to keep as-is, add a warning to, or remove outright this web reference. If it indeed has significant errors, I would lean towards removing it, but I don't feel that the case for that has been proven. So for now I feel that the link should be kept without warnings.

--EMS | Talk 15:13, 16 Jun 2005 (UTC)

---

There can be no doubt that Sag A* is a gravitationally collapsed object, and that if GR is correct it is a black hole. The same also applies to the other super-massive objects in the centers of galaxies. I just don't think that there is a consensus that these really are black holes, at least amongst astronomers. However, that said, I will also admit that any scenario explaining how these objects could be something else is speculative. (I don't believe in black holes myself, btw. Even so, I also admit that GR is the best theory we have at this time. I just want the record to be straight in that I am not alone in not liking or accepting the black hole as physical reality.)

That said, I will concede that if the text is saying that nothing that ceratinly is a black hole (if GR is correct) is known, that is not correct.

For the quantum state business, I will point out that an expanding light sphere is composed of numerous photons. My focus is on each one.

As for the boson/photon business, I need more context to be sure of the mix-up, but the offending sentence does indict itself.

Beyond that, I think that the greatest indictment is in your last paragraph about the work as a whole. This seems to be an ancient reference, predating Chris Hillman's reworking of things.

Finally, it is good to see that the "culprit" is you. However, my feeling is that either we keep this reference or we don't. There are plenty of good resources out there. We don't need to reference an inadequate one. --EMS | Talk 17:31, 16 Jun 2005 (UTC)

removal of threads

Dear "CyclopsX",

The "Spacetime Myth" thread is a part of this record for better or worse. If you find it embarassing, then so be it. My advice is to leave it alone, and stop calling attention to it. --EMS | Talk 03:28, 17 Jun 2005 (UTC)

Rewrite ready

I have finally gotten around to doing a rewrite of this article. The draft is at User:Ems57fcva/sandbox/General_relativity_2. Comments/suggestions/complaints are appreciated. Outright edits can also be done (as with most any other Wikipedia entry). All that I ask is that an explanation is given in the edit summary and/or the associated talk page (which does not exist yet, but that should not stop anyone from creating it).

As you will see, this rewrite takes a fairly different tack than the current article. In my view it does a better job of describing what general relativity is all about. The features include:

• an abbreviated introduction/lead,
• a sectioned-out overview of the primary features of GR,
• a sectioned and list-based overview of the important predictions of GR,
• a sectioned and detailed overview of how GR differs from classical mechanics and SR,
• a new Status section, and
• an abbreviated references section, with most of the prior material having been moved to a new page entitled "general relativity resources", which is also for now in my user space.

Please don't "promote" this on your own. I will do so once I am sure that there is no objection to my doing so. Or if you do, please read and implement the "TO DO" list in the comments at the top of the page. (I disconnected some category-related stuff so that this draft would not appear in the category pages.) --EMS | Talk 04:24, 11 July 2005 (UTC)

I'm afraid I won't be in a position to comment on this until much later in the week. However, if you're still looking for checking at that time, I'll do what I can to contribute. --Christopher Thomas 20:24, 11 July 2005 (UTC)

---

For some reason I cannot currently save edits to the talk page associated with the rewrite. If others are having the same trouble, then let's try putting comments here. I have put in a bug report on this in the meantime. --EMS | Talk 01:27, 13 July 2005 (UTC)

This issue seems to have been resolved. --EMS | Talk 03:01, 13 July 2005 (UTC)

Last Call

Unless there is an objection, I will most likely move the rewrite over on Monday evening [Eastern (USA) time].

There have been some changes to it, but nothing dramatic. --EMS | Talk 02:18, 16 July 2005 (UTC)

Done

" 'The time has come ...' " - From The Walrus and the Carpenter by Lewis Carroll.

The rewrite has been moved. Don't say that you weren't warned.

I will admit that this is not a final product and that I am still tweaking it a bit. Then again, in Wikipedia nothing is a final product. --EMS | Talk 22:59, 18 July 2005 (UTC)

Thoughts

1. Should the GIF of spacetime being warped be moved down to the Spacetime as a curved Lorentzian manifold section?
2. For the Classical mechanics and special relativity section: Should an article be created on the principle of minimal coupling, and the Conservation of energy-momentum and Electromagnetism sections placed under it, with the content for those sections in this article being reduced to "See principle of minimal coupling"?

For idea 2:

• The advantage is that
  • this shortens the article even more and
  • removes some of the more abstract math.
• The disadvantages are that
  • it breaks up the comparison with classical mechanics and special relativity and
  • hides some useful information.

So my tempatation is to do idea 1 but not idea 2. --EMS | Talk 04:21, 19 July 2005 (UTC)

• Some time ago, the GIF was not at the top of the article; I moved it to the top to grab the reader's attention. I can understand why it might be good to move it down to the section you mentioned, but I think for an encyclopedia article, grabbing someone's attention is probably more important.

I can live with that. --EMS | Talk 15:51, 20 July 2005 (UTC)

• I noticed you gave an example of geodesic deviation (GD) (two people head due North etc...); is this technically GD? I mean, the paths meet because of the Earth's curvature. I thought that GD referred specifically to gravity (although I agree that the point is that lines cross due to curvature) - this is just a question of terminology. It's not strictly an example (two balls falling - and converging - in the Earth's gravitational field would be an example of GD). I think perhaps, 'this analogy illustrates the idea of geodesic deviation' may be better technically. Also, 'GD is used as an alternative to gravity' is potentially misleading. I think this needs a little explanation or the wording needs to be changed.

I strongly assure you that geodesic deviation is an attribute of any curved manifold. That is why using the surface of the Earth is a good way of illustrating it. The difference is that the surface of a sphere is a 2-dimensional Riemannian manifold while spacetime is a 4-dimensional Lorentzian manifold. However, for both manifolds geodesic deviation is as I defined it in the article: The tendency of intially parallel paths to become non-parallel as they are geodesically extended along the manifold.

That paragraph could use a little work though. The mention of "geodesic deviation" is sundered from its definition (which should just preceed it), and your balls gedanken is a good way of showing how the concept is extended into GR itself. --EMS | Talk 15:51, 20 July 2005 (UTC)

• As regards your Idea 2, it depends on how much should go into a possible principle of minimal coupling article. If it is only intended that the two sections you mentioned are to go in this possible new article, then maybe it's not worth creating a new article, unless more details and explanations are given (than is currently in the two sections). On the other hand, the new article is bound to be expanded. Maybe more examples could be given - does the principle of minimal coupling hold exclusively ? Are there (quantum or non-quantum) examples that violate the principle of minimal coupling ? --Mpatel 09:23, 20 July 2005 (UTC)

I think that you are echoing my own thoughts on this matter. Let's leave it be for now, until we have more of a sense of what the fuller article would achieve. --EMS | Talk 15:51, 20 July 2005 (UTC)

"ad hoc" remark

Mpatel -

I think that your remark about the cosomological constant being "ad hoc" would be better placed in the History of general relativity article. I would prefer to find ways to contract the History section of this article, while details such as this remark are used to expand and fully flesh out the History of GR article. --EMS | Talk 16:04, 20 July 2005 (UTC)

Ok, I'll do just that. ---Mpatel 16:09, 20 July 2005 (UTC)

Thank you. --EMS | Talk 16:34, 20 July 2005 (UTC)

Proposal

I agree that the physical cosmology template shouldn't really have been on this page. However, let me propose that someone make a Template:Gravity or Template:General Relativity with links to gravity, general relativity, tests of general relativity, equivalence principle, Schwarzschild metric, black hole, Friedmann-Lemaître-Robertson-Walker, gravitational singularity, gravitational radiation, event horizon, etc, and also a reciprocal link to physical cosmology, which is closely related (although also closely related to astrophysics and particle physics). Comments? –Joke137 15:12, 22 July 2005 (UTC)

Not a bad idea. However, I would have this be a GR template and leave gravity out of it. My complaint is similar to that of GR being listed as a part of physical cosmology: There is a lot more to gravity than GR, just as there is a lot more to GR than cosmology. Whatever is placed into that template's box should fit neatly into the corresponding conceptual "box". (I disagree with GR being restored to the physical cosmology template for that reason btw.)

Also note that as a rule, every article listed in the box should be tagged with that template. (This is another reason why the GR article should not be in the cosmology template given that you concede that the template should not be on the GR page.) Perhaps the template can contain a "Related topics" section listing relevant articles that do not fit into the box and therefore lack the template. That may be acceptable as the means by which cross-navigation occurs.

I also counsel you to leave event horizon and gravitational singularity out of the GR list. Those are sub-topics of black hole, and so are not appropriate to a list of high-level GR articles. OTOH, Kerr metric should be included. --EMS | Talk 15:42, 22 July 2005 (UTC)

Here is an attempt Template:General relativity. I modelled it after (i.e. stole it from) the Template:Cosmology. I think that gravitational singularity and event horizon are both more general than black holes, and are fundamental, important topics in GR. For example, even horizons occur in de Sitter space and singularities occur in FLRW space. They are fundamental to the causal structure (e.g. the Penrose diagram) of spacetime (which should have an article, but doesn't) and the Hawking singularity theorems are probably the most important development in theoretical relativity of the latter half of the twentieth century. In any case, I thought I would make a template and hash this out before starting to add the template to pages. –Joke137 18:58, 22 July 2005 (UTC)

I have modified the template to group the "core" articles together. I think that it will do. As for event horizon and gravitational singularity, I have decided that the issue is that I hate black holes with a purple passion, and therefore just should not be touching that issue. So if you are sure that those belong there, then so be it.

I leave it up to you to populate the pages with the new template. --EMS | Talk 20:29, 22 July 2005 (UTC)

I like your changes. I am curious why you hate black holes. I actually think the notion of "singularity" and "event horizon" are more fundamental to GR than black hole, in some sense, and I was thinking of putting the black hole down with related topics... –Joke137 20:32, 22 July 2005 (UTC)

I advise against doing "Black hole" as a related topic. It is too bound up with the other topics and is a central topic relating to GR both popularly and academicly. As for why I dislike them: I will respond on your talk page. Black holes are a theorem of GR, and in the article space that is all that matters. --EMS | Talk 21:11, 22 July 2005 (UTC)

I haven't been following this until today, and don't really want to pay much attention even now (plate too full), but FWIW, Joke137 is clearly completely correct in saying that both horizons (event, Cauchy) and curvature singularities are emphatically more general than the notion of black hole. EMS, it is a very good thing that you self-censor your "hatred" of black holes in the gtr pages, and I very much hope you can continue to do that, despite the apparent strength of your feelings. Maybe you can set a model, showing that even individuals with maverick opinions can make useful improvments as long as they can keep strictly separate the task of motivating their own maverick ideas from the task of explaining as clearly and fairly as possible a body of well-established theory (e.g. the gtr pages).---CH (talk) 02:22, 14 August 2005 (UTC)

Inertial frame of reference article

Can people kindly look at inertial frame of reference, and even if you don't want to change it at least watch it for a while? I just did a major revert from this version and I think that it would be wise to ensure that it does not reappear. Suffice it to say that any GR-related stuff on other pages needs to be kept "in line".

I have dealt before with the editor who did the rewrite of March 6 (when most of the egregious material appeared). He means well, but does not know what he does not know. I do not know how much support the previous version will have, but I would like people to be ready to defend the reversion just-in-case.

Thanks everyone. --EMS | Talk 02:46, 2 August 2005 (UTC)

General theories of relativity (new article by ErkDemon)

This article has been created and flagged as dubious. I thought those here would be well placed to comment.The primary author is ErkDemon.

Hi, all, just to clarify: ErkDemon created the article General theories of relativity, and I put up a "dispute" flag, left a message on his talk page, and left a longer message on Talk:General theories of relativity. I encourage anyone interested to join in the discussion, but please, do it in the right talk page! TIA---CH (talk) 02:01, 14 August 2005 (UTC)