Talk:Introduction to general relativity/Archive 4

message: * We should try to avoid unfamiliar technical terms and concepts.  Instead, we should prefer familiar, everyday ones or at least ones that are easily visualized or commonly found in the popular press, such as black hole and Big Bang.
* Ideally, each section would be linked conceptually to the one following it, so that the reader has the sense of flow and building on their earlier work.
*  We should not ask the reader to absorb too much in any one sentence.  Brevity can be sacrificed in favor of clarity and a slower pacing. 
:*Our watchword should be : as long as necessary; as short as possible.  It's easy to get carried away adding more and more details; let's leave out what we can leave out without distorting our account of general relativity. -- Markus Poessel 07:23, 19 July 2007 (UTC)
thread_title: Style suggestions

message: As ever with vertical-format Navboxes -  is making it hard to format images for all displays - I've got a wide format and it looks pretty bad. I've suggested reformating the template so it spans. Any opinions? Please comment here. regards --Joopercoopers 13:27, 18 July 2007 (UTC)
replies: text: The box looks very crowded. Can you do a horizontal one at the bottom of the page? Is that what you meant by "spans"? Awadewit | talk 14:22, 18 July 2007 (UTC)
replies: text: yeah - something like this maybe - without the hide function --Joopercoopers 14:48, 18 July 2007 (UTC)
replies: text: That is what I was thinking of (I like the hide function, but, whatever. I'm certainly not going to start saying ridiculous things like "This article cannot be an FA without a "hide" function in the navbox.). Awadewit | talk 14:54, 18 July 2007 (UTC)
replies: text: Go no - nothing to do with the FAC, just a nicety. Actually perhaps more something along these lines.... --Joopercoopers 14:57, 18 July 2007 (UTC)
thread_title: Navbox

message: Hi,
The sister of this article, Introduction to special relativity, is in need of work. I've worked on it to clearly motivate special relativity and have tried to build geometric intuition to explain the counterintuitive concepts. Now I need some of the people who have done so much wonderful work in this article to bring Intro to SR upto GA status. It is currently rather focussed and needs to be rounded out to provide a self-contained introduction. The language can also probably do with some brush-ups. Thanks. Loom91 06:48, 30 July 2007 (UTC)
replies: text: *Thanks for the invitation.  At the moment, I'm focusing on the other sister article (general relativity), but once I've done more of what I mean to do there, I'll have a look at "Intro to SR". --Markus Poessel 06:24, 1 August 2007 (UTC)

text: *While progress on the re-working seems to have slowed down, I still want to go through the whole article bit by bit. If things stay as quiet as they are now, I will probably just go ahead with gradual changes, and once I've reached the section you mention, I do think it can be simplified (the Einstein tensor is needed for the equation, though; I also do not think that the typical reader of the article will be confused by the boldface - abstract indices would look much more scary and distracting, would be my guess). --Markus Poessel 06:24, 1 August 2007 (UTC)
replies: text: *Why do you think G is needed for the equation? The equation can be written out in terms of the Ricci tensor, ricci scalar, metric tensor and the cosmological constant. Since the Ricci tensor and the metric tensor have already been explained, that would be clearer. Also, using indices will help the reader avoid the misconception that the Einstein field equation is one equation in the ordinary sense. To readers not familiar with matrix equations, writing a collection of equations as one equation may not be very clear. Loom91 07:16, 1 August 2007 (UTC)
replies: text: *As far as I can see, the Ricci tensor hasn't been explained. Neither has the Ricci scalar. Indices will help some readers realize that this is more than one equation (the others will just have to read the text), but the indices will certainly confuse other readers.  I'd like to keep the equation as simple as possible - I think that if we write down the more complicated form, readers will not even see the part they can understand, e.g. how all the constants appear so neatly in the equation. --Markus Poessel 18:42, 1 August 2007 (UTC)

text: The Riemann tensor is briefly mentioned, yes.  The Ricci tensor isn't explained at all.  Neither Riemann nor the metric have been given in terms of components.  If we write the Einstein equations in terms of Riemann the metric, it will be rather longish, and it will look like nothing that the reader can possibly understand with the information we have given him or her.  Indices, especially Einstein summation, will add to the confusion - if you have no idea what vector components are, what can you be expected to make of these indices?  And why are some indices up, others down?  The fact that they are "merely notation" seems to me to be a good reason to avoid them, if we can. If there are indices, readers will feel that there is something they should understand at this point, but cannot.  If there are merely symbols T and G in boldface, readers are more likely to feel that all they are meant to understand is what is written in the text about these symbols - and they would be right. Mentioning that G can be written in terms of Riemann and the metric sounds sensible, though. --Markus Poessel 18:42, 2 August 2007 (UTC)
replies: text:  How about giving the expression for G in a separate line and explaining that it is ultimately a functional of the metric and therefore the EFE are a set of equations relating various derivatives of the metric to the energy content of space? Loom91 14:39, 3 August 2007 (UTC)
replies: text: If by "giving the expression for G", you mean writing down the formula, again, I think this would be more confusing than helpful.  I agree, though, that mentioning that Riemann and G depend on the derivatives of the metric might be good (if only in parentheses). --Markus Poessel 16:19, 7 August 2007 (UTC)
thread_title:  Help at [[Introduction to special relativity]] 

message: The part about Equivalence Principle reads:
"roughly speaking, this principle states that a person in a free-falling elevator cannot tell that they are in free fall; every experiment in such a free-falling environment has the same results as it would if the observer were at rest or moving uniformly."
This is confounding me. I think what it's saying is that a person in a gravity-free environment can't tell if they are in a freefall or in space; the effects are the same. However, to me, it seems to say that a person in freefall can't tell if they're in freefall or resting on the ground. I think it would be more clear if it read:
"roughly speaking, this principle states that a person in a free-falling elevator cannot tell that they are in free fall; every experiment in such a free-falling environment has the same results as it would if the observer were in space or moving uniformly."
However, I don't feel comfortable making this change. TribeCalledQuest 12:26, 7 August 2007 (UTC)
replies: text: Thanks for the feedback.  You're right in that the reference to space went missing.  It should be "at rest (or moving uniformly) in deep space, far from all sources of gravity", which I've now put in.  Thanks again! --Markus Poessel 16:14, 7 August 2007 (UTC)
replies: text: Much clearer, and thanks to all for a well-written article. TribeCalledQuest 19:56, 7 August 2007 (UTC)
thread_title:  Confusing sentence 

message: That articles has again undergone some major work, and I feel is in a much better state. Before I apply for GA status, I'll be grateful if other editors review the article. In particular, it needs a few sections more fleshed out to give a well-rounded overview like this article, and it may also need some tinkering with the tone to make sure it reads more like an encyclopedia article than a textbook explanation. Thanks. Loom91 10:39, 4 October 2007 (UTC)
thread_title:  [[Introduction to special relativity]] 

message: Here's a thought - since this article is the introduction article, should the link to quantum mechanics also link to its introduction article? Not saying yes, just raising the question.71.37.28.223 (talk) 14:47, 28 February 2008 (UTC)
replies: text: Sounds good. Done. Markus Poessel (talk) 01:01, 29 February 2008 (UTC)
thread_title:  Introduction articles 

message: ===Introduction to general relativity===
Fails featured article criterion 1a because it's not well written. 66.68.23.41 (talk) 18:42, 6 September 2008 (UTC)
replies: text: Correcting malformed FAR listing.  18:51, 6 September 2008 (UTC)
thread_title:  FAR listing 

message: Fails featured article criterion 1a because it's not well written. 66.68.23.41 (talk) 18:42, 6 September 2008 (UTC)
replies: text: Correcting malformed FAR listing.  18:51, 6 September 2008 (UTC)
thread_title: [[Introduction to general relativity]]

message: Could whoever added
"Einstein's theory of gravitation is not only a formal mathematical development, it also rests on assumptions of deep cosmic significance. [Lincoln Barnett The Universe and Dr. Einstein, p. 85, Bantam Books Inc., 1972 ASIN: B0017TOEXC]" 
please give some background information about what is meant by the sentence? I didn't get it, so I took it out for the moment. (The article is currently undergoing FAR, and I'm going through the whole text, making sure the prose flows smoothly, and this was one of the places where it didn't.) Markus Poessel (talk) 15:34, 13 September 2008 (UTC)
thread_title:  Cosmological section  

message: I don't remember ever seeing an article written by experts that was so accessible to the lay person (like myself!).  --Doradus (talk) 01:28, 18 April 2010 (UTC)
thread_title:  Nice job 

message: This article passed at FAC about three years ago. A quick review of the article reveals thirteen paragraphs have no citations, about a dozen other long ones have only single citations, and a few other editorial and MOS violations, including phrases like "It is important to stress...", five paragraph lead, half the images are possible WP:OR with no sources listed on the image pages. There is a whole host of general references, not at all used in the citations. In short the current referencing of this article would not qualify for a good article, let alone a featured one. I do note that the review points out the authors of this article were experts, so that is worth something. —Charles Edward (Talk | Contribs) 02:18, 18 April 2010 (UTC)
thread_title:  A concern 

message: When is the LISA Pathfinder to be launched? ESA gives <S>two
actually three dates: 2012, and June 2011 and March 2010. Should be rectified here, in the LISA Pathfinder article and in all other relevant articles. --Eleassar my talk 09:13, 18 April 2010 (UTC)
thread_title: LISA Pathfinder: launch date?

message: It appears somoene has decided to edit the box with the equation and other links by titling it "General Relativity Is Awesome".  I can't figure out how to edit that headline.  It's quite obviously vandalism.  Anyone want to edit the garbage out?99.40.240.70 (talk)  —Preceding undated comment added 00:00, 19 April 2010 (UTC)
thread_title:  Vandalism 

message: Re. "Experimental tests" section:
The animation  is terrible.
It shows the planet's orbit precessing by one revolution for every orbital period of the planet, which is far too fast (at least under "normal" conditions). 
For example, the perihelion of Mercury only moves a tiny amount per Mercurian year.
It is true that Newtonian gravitation predicts a fixed elliptical orbit of a single planet around a spherical star. However, in the case of Mercury, Newtonian physics predicts a small rate of precession, and General Relativity corrects this by less than 1% - see Tests_of_general_relativity#Perihelion_precession_of_Mercury. So in that case, both orbits should precess at nearly the same rate.
Also, the size of the obits changes as the loop proceeds, presumably due to scaling each frame to completely fill the box.
The file is also extremely slow to load in Chrome on a Mac, and very jerky.
Surely somebody can do better than this?
131.236.43.48 (talk) 05:37, 19 April 2010 (UTC)
thread_title:  Experimental tests: Orbit: bad animation "Newtonianvseinsteinianorbits.gif" 

message: Fantastic article! But can a deceased person be called "doyen"? If this is the case, wouldn't the big E himself challenge Wheeler for the title? :-) 131.236.43.48 (talk) 05:37, 19 April 2010 (UTC)
replies: text: I have removed the non-encyclopedic (read fanclub) phrase. Good catch. DVdm (talk) 10:44, 19 April 2010 (UTC)
thread_title:  Doyen? 

message: Regarding the discussion about "Introduction to..." articles at this article's Featured article candidacy discussion, I've followed the kind advice given by some of you and made my argument into an essay, which is now online as Wikipedia:Many things to many people.
(Strangely, I could have sworn I wrote something like this yesterday evening. No record of it, though... may be forgot to press "save page".) --Markus Poessel
Separating the overly technical details from the general information is useful and necessary.  However, this article should be called General Relativity and should be the first thing people see when inquiring about the subject.  While Wikipedia is many things to many people, most (greater than 80%) accessing any given general topic page are interested in an encyclopedic overview of the topic and then a minority of specialists look for highly specialized, technical or detailed information.  This article should be called General Relativity.  Searches and links should bring readers to this article.  Then the minority, the specialists and those interested in further reading should click an additional link to the a page called, "General Relativity in Detail" or something along those lines. --Mike padilla (talk) 18:14, 20 April 2010 (UTC)
thread_title:  "Introduction to" articles 

message: I used the toolserver.org to check this article and found (here) two dead links. Please update links. Earthandmoon (talk) 11:22, 31 August 2010 (UTC)
thread_title: Fix links

message: In the part of "physical consequences" it says
"the second observer will measure a lower frequency for the light than the first"
but there is no mentioning before of which observer is the first and which is the second Dy yol 19:08, 8 September 2007 (UTC)
replies: text: Hello, unsigned editor. The answer is, in fact, no. The easiest way to see this is to follow the link (Harrison 2002) given in that particular section; that sketches how the shift follows from the equivalence principle. Markus Poessel (talk) 13:27, 23 March 2008 (UTC)

text: Another way to look at it: since an accelerated frame is equivalent to a uniform gravitational field, points higher in that "equivalent g-field" must have higher "equivalent gravitational potential energy" than lower points.  So the assertion that points in an accelerated frame are at the same potential must be false.  Wwheaton (talk) 19:15, 23 March 2008 (UTC)
replies: text: Perfectly correct. What I like about the p.o.v. I cited is that it doesn't require you to know anything about potentials or somesuch, and uses what I think is the simpler version of the equivalence principle (the one that translates directly to geometry - local flatness). Markus Poessel (talk) 22:44, 23 March 2008 (UTC)

text: You're welcome.  A more practical tip: if you add four tildes at the end of a comment, like this: ~~~~, this will be automatically transformed into your signature (with link to your user page) and date. It's a standard way of signing stuff on Wikipedia. Here's what it looks like when I do this, right now: Markus Poessel (talk) 00:57, 27 March 2008 (UTC)
thread_title:  Part need clarification 

message: Great article! (Though does use of the word apodictically really add to what is a beginners' article?)
I would like to see a paragraph explaining the apparent contradiction between (quoting from the article), "Gravitational waves, a direct consequence of Einstein's theory, are distortions of geometry that propagate at the speed of light,..." and "When mass is concentrated into a sufficiently compact region of space, general relativity predicts the formation of a black hole – a region of space with a gravitational attraction so strong that not even light can escape." In other words, if a black hole can trap light, why doesn't it trap gravity as well?
I wish my Physics was strong enough to add this, but it isn't.
Thank you! Laguna CA (talk) 23:13, 5 July 2012 (UTC)
thread_title:  Apparent Contradiction 

message: I'm beginning a sort of WP:Expert review process for articles independent of the featured article system which I've realized has problems. As such, I've rated this article a level 'A' which means it is of the quality that would be expected from a professional reference work on the subject. I say this as a person with graduate degrees in astrophysics, but I encourage others who have similar qualifications to make comments if they believe my judgement to be incorrect.
jps (talk) 02:16, 12 September 2013 (UTC)
thread_title: WP:PHYSICS review: A-level article

message: As a former prof in the physical sciences, and so nearer to the average reader than an astrophysicist, I have to disagree with the foregoing assessment. Per the tags of this day, the article reads like a professorial or graduate essay, written by one or ones with great confidence in their knowledge base, and without a felt need to provide the sources for the stated facts and perspectives that appear. This is not WP policy.
The content of this article, even watered down as it is form the main article, is not common knowledge, certainly for no complete body of students that I have dealt with (though I have been at fine institutions), and not for my 15 year old science-studying nephew, who's is the clearer target of encyclopedic science articles.
No, one citation per paragraph, offering broad ideas of places for Further reading—this is not sourcing of content to the experts from which the material is drawn.  One has to conclude that the individuals writing this perceive themselves as adequately expert to craft this final text, without having to anchor its facts and perspectives in good secondary sources. But again, this is not Wikipedia policy.
References to secondary sources, within a page or two of the fact or perspective being cited. And all facts and perspectives sourced. These are the reasonable WP expectations of encyclopedic writing, even for articles that have had no history of approaching their topics truly in an encyclopedic way.
In any case, happy holiday. The anniversary, that is. And the national one as well.
Le Prof  Leprof 7272 (talk) 03:34, 26 November 2015 (UTC)
replies: text: I was not involved in writing this article and have very little interest in this topic, except for protecting a WP:FA from rogue editing. Leprof 7272, your long message says almost nothing, please focus and provide specific comments on the article content. Your "refimprove" and "no footnotes" tags are not appropriate: the article contains ample amount of footnotes and no facts challenged with "citation needed". As to the comment by IP:73.210.154.39, Template:Page_numbers_improve is just a template, not a policy or guideline. Many cited chapters are several pages long; while I agree that more specific page numbers would help the reader, the citation is not dire. Materialscientist (talk) 03:43, 26 November 2015 (UTC)
thread_title: Edits of this day

message: I thought I was following things fairly well until I got to the "gravitational frequency shift of light" paragraph.  I just may not be very smart, but the fact that gravity would have any effect on light is a surprise to me.  An "object in a gravitational field should feel a gravitational force proportional to its mass" -- that makes sense to me.  But if that means that light has mass, maybe that should be discussed a little.  Also, an explanation of why the gravitational force changes the frequency, rather than just changing the direction of the light beam.  
Fulto006 (talk) 01:22, 28 December 2015 (UTC)
thread_title:  gravitational frequency shift of light 

message: Hello fellow Wikipedians,
I have just modified 4 external links on Introduction to general relativity. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
*Added archive https://web.archive.org/web/20070704102558/http://relativity.livingreviews.org/Articles/lrr-2003-1/index.html to http://relativity.livingreviews.org/Articles/lrr-2003-1/index.html
*Added archive https://web.archive.org/web/20070617115947/http://imagine.gsfc.nasa.gov/docs/features/news/grav_lens.html to http://imagine.gsfc.nasa.gov/docs/features/news/grav_lens.html
*Added archive https://archive.is/20121206023615/http://www.iam.ubc.ca/old_pages/newbury/lenses/research.html to http://www.iam.ubc.ca/old_pages/newbury/lenses/research.html
*Added archive https://web.archive.org/web/20070629140354/http://www.europhysicsnews.com/full/42/article4.pdf to http://www.europhysicsnews.com/full/42/article4.pdf
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thread_title:  External links modified