Talk:General relativity/Archive 4

message: Whoa--- I certainly don't agree that exact solutions = physical comoslogy! But over all, this is a nice article--- certainly more stylish than the English one.  EMS, at first it seems too short/limited compared with yours, which is much more ambitious, but the comment about EP and that NASA plane that flies in a parabolic arc to "cancel" Earth gravity might be worth adding somewhere---CH  (talk) 01:57, 14 August 2005 (UTC)
thread_title:  Relativité générale 

message: The following was added to end of the black hole section, describing Hawking radiation:
: (A form of radiation believed to emanate from black holes, arising from the creation of pairs of subatomic particles in the space adjacent to the black hole, with one particle falling into the black hole and the other radiating away. The energy lost to such radiated particles is believed to cause the eventual disappearance of the black hole).
There is nothing wrong with the text itself.  Instead my complaint is that it is covering ground that is already and more appropriately covered in the Hawking radiation article itself.  This is an overview article.  If it is expanded, it should be by mentioning additional phenomena and not by elaborating on what is already here.  --EMS | Talk 14:37, 24 August 2005 (UTC)
thread_title:  Hawking radiation explanation 

message: At the start, it's stated that 'Spacetime is curved by... (or stress-energy)...'. The stress-energy link goes to the tensor, but this renders the sentence misleading as it suggests that spacetime is curved by the tensor - but, in a way, maybe this is ok, as the spacetime is an abstraction, as is the tensor, so 'spacetime is curved by stress-energy' actually does make (abstract) sense. This is a very subtle point, but one I believe worth correcting. Perhaps I'm digging further than is necessary here, but I think the statement should be changed to, 'Spacetime is curved by...(described by the stress-energy tensor)...'. But maybe this is too detailed at the start. Hmmmm. Am I making any sense at all here ? I think I might be tired... ---Mpatel  (talk) 17:21, August 25, 2005 (UTC)
: The full statement is 
:: Spacetime is curved by the presence of mass, energy, and momentum (or stress-energy) within it.
: So stress-energy is a certain combination of the mass, energy, and momentum in the spacetime.  That said, you have run up against one of the weak points in this article:  The semantics of the relationship between "mass, energy, and momentum" and curvature.  I have chosen to use the term "stress-energy" to package up "mass, energy, and momentum" since other sources refer to stress-energy too, and have carried that syntax forward into the rest of the article.  So I am at that point introducing "stess-energy" as a compact term for "mass, energy, and momentum", with an oh-by-the-way-it-is-described-with-a-tesor added in.
:The problem is that I include momentum in the list of things that affect spacetime.  Most people think of mass-energy but momentum is also a part of the picture, and so I refuse to leave it out.
: So you have a point there, but I don't think that your initial idea is going to work.  At the least please be aware that changes to that sentence may affect how the rest of the article is read.  OTOH, I would like to find a better way of achieving the same result. --EMS | Talk 19:34, 25 August 2005 (UTC)
thread_title:  Spacetime curved by stress-energy (not the tensor) 

message: there used to be a section for external links that had at least two references that this neophyte found useful:
The Meaning of Einstein's Equation
No-Nonsense Introduction to General Relativity
can such a section be restored at the bottom of the article.  also, i would include this quote, a plain language meaning of the EFE, explicitly in the section of EFE:
 Given a small ball of freely falling test particles initially at rest with respect to each other, the rate at which it begins to shrink is proportional to its volume times: the energy density at the center of the ball, plus the pressure in the x direction at that point, plus the pressure in the y direction, plus the pressure in the z direction. 
if the wikipedia GR article is meant to be a tutorial for boneheads like me, would this not be useful?
r b-j 21:21, 25 August 2005 (UTC)
replies: text: The material that you are asking about got exported to general relativity resources, and is featured under the category "web tutorials" there.  --EMS | Talk 03:16, 26 August 2005 (UTC)
thread_title:  External Links - GR tutorials 

message: Regarding making this page a featured article, I still think an awful lot of work needs to be done. EMS' revision constituted an outstanding improvement over the previous versions. If we are looking for featured article status, whilst trying to stick to the conventions of the GTR project, then the bar is really being raised quite high. One point for improvement that should render the article more elegant is to reduce (eliminate?) the 'bullet-point' approach, especially at the start, as I think it looks ugly. ---Mpatel  (talk) 17:32, September 1, 2005 (UTC)
: I tried to do a paragraph style write-up, and ended up with an unreadable morass.  I was not after beauty.  I was after an effective mechanism for separating out the important points of the theory.  --EMS | Talk 03:52, 7 September 2005 (UTC)
thread_title:  Featured article status 

message: User:JimJast put in some "tidying" that I consider a bit off the point. Sorry, Jim, but your explanation with c varying kind of leads readers down the garden path to dealing with the coordinate velocity of light. Its velocity in any inertial frame is defined to be 299 792 458 m/s. Using coordinate-velocity in a rigid frame, one can play with simplified ways to understand GR (varying mass-energy) but really the mass energy of a piece of rock, e.g. should be considered as just m c^2 where m is the rest mass.  Using changing rest mass-energy can be worked out and used in some cases, such as in the solar system, by using a rigid reference system, but look at the contrast to the description down the page of a person standing on Earth. Pdn 00:41, 2 September 2005 (UTC)
thread_title:  Reversed edits by JimJast  

message: I added to this section the predictions resulting from replacing the present assumption of non conservation of energy in GR with assumption of strict conservation of energy (and so necessarily also replacing the Riemannian geometry with a different geometry of spacetime with proposed by Einstein in 1950 non symmetric metric). Those predictions resulting from strict consrvation of energy seem interesting enough not to be hidden from the readers however I expect that lots of people will hate them. I'd appreciate those people discussing the matter with me before reversing my edits. Thank you. Jim 14:01, 3 September 2005 (UTC)
replies: text: Wikipedia is an encyclopedia, not a bulliten board.  (See Wikipedia:What Wikipedia is not for more clarification.)  The predictions that you were trying to present are not predictions of general relativity.  Because of that, they are wholely inappropriate, and were immediately reverted for just that reason.  The involvement of Einstein is irrelevant to this.  --EMS | Talk 03:48, 7 September 2005 (UTC)
thread_title:  Expanding section of the article on "cosmological predictions" 

message: I've just seen some anon adding a cleanuo tag to this section, and I must confess, I find the section somewhat strange. All those alternative explanations of redshift should go to non-mainstream cosmology. And perhaps I'm only having a abd day, but can't this section be deleted entirely? Or replaced by Mathematics of general relativity? --Pjacobi 13:04, September 8, 2005 (UTC)
: I have reverted the section to it's form of two weeks ago.  I don't know how that extra stuff (apparently of JimJast's) got overlooked, but that is taken care of now. --EMS | Talk 18:36, 8 September 2005 (UTC)
thread_title:  The mathematics of general relativity 

message: We need to exercise dilligence in watching this page.  Recently, a user decided that a speculation which he claims was embraced by Einstein in 1950 should be enshrined in this page, instead of being placed in a separate article on the speculation itself.  To do so, that user made changes to the sections on "Predictions of general relativity" and also on the "Mathematics of general relativity".  The changes to the Predictions section were caught at the time, but not the ones to the Mathematics section.
It is important that whenever a change to this page is detected in the watchlist that not only the current change be reviewed but also that the "History" tab be used to determine what all has been happenning to the page since the page was last checked by yourself.  The totality of those edits should have been reverted out at the time.  It is much more of a nuisance to come back later and need to determine how to fix the article while preserving newer and usable edits.
--EMS | Talk 18:48, 8 September 2005 (UTC)
thread_title:  Dilligence needed 

message: From the above discussion:
: ...If you like, the word "published" can be replaced by "completed", but in terms of changing that line that is all that I see as appropriate. --EMS | Talk 15:57, 2 November 2005 (UTC)
replies: text:  Thanks ems, finally a constructive remark! Indeed, I don't think it suffices but it's a lot better like that, please go ahead. And then I will not insist anymore, I think we all wasted too much time about just one sentence! Cheers, Harald88 19:03, 2 November 2005 (UTC)

text: well he did publish it then, but who knows what completed means. --MarSch 12:42, 3 November 2005 (UTC)
replies: text:  I do see that as an issue too.  I also remain bothered by Harald88 showing signs that he does not really get when GR is about, including the intimate relationship between acceleration and gravitation in GR.  Harald88 may also be looking at the 1916 Annalen der Physik article as the actual publication of GR, whereas I see it as a post-mortem on the results of the research that led to GR.  As I see it (and I think that you will agree with this), the 11/25/1915 article was the completion of GR including its publication, with GR at that point being completely known and published due to Einstein's previous articles on subject. --EMS | Talk 14:48, 3 November 2005 (UTC)
thread_title:  Possible change to the first line 

message: I am trying to have this category deleted and most of its entries placed into :category:general relativity.  I figure that others who are involved with GR will want to have a say in this. --EMS | Talk 15:11, 14 November 2005 (UTC)
thread_title:  [[:category:effects of gravity]] 

message: This new section does not belong here (it is too specific for this overview article), but it does not deserve to be deleted outright.  Instead it should be in its own article and can be referenced by this one.  (We need an article with graphics like that showing how we conceptually go from classical mechanics to general relativity, and that is a start at such a thing.)  Are there any suggestions on what to call the article that would hold this material?  Or other suggestions of what to do with it. --EMS | Talk 21:39, 28 December 2005 (UTC)
replies: text: Not happy about the location of the revised new section. At the moment, it breaks right into the discussion of GR. If anything, it belongs in the 'Relationship to other physical theories' section further down in the article. MP   (talk) 08:34, 29 December 2005 (UTC)

text: Ok, I've moved the section further down. The 2 equations may be redundant, as they are properly discussed in the relevant article. How about removing them and replacing them with some words instead ? MP   (talk) 08:46, 29 December 2005 (UTC)

text: Done Complexica 16:26, 29 December 2005 (UTC)
thread_title:  The non-relativistic example 

message: In this subsection, the first sentence talks about alternative classical theories of gravitation; however, there is mention of a Fierz-Pauli spin-two theory, which is decidedly described as a quantum theory. Should this theory be mentioned here ? Maybe it's better to mention it in the QM section. MP   (talk) 09:10, 29 December 2005 (UTC)
thread_title:  Alternative theories