Talk:Introduction to general relativity/Archive 3

Lead
All concerns regarding the lead should be listed here. Awadewit | talk  11:46, 18 July 2007 (UTC)


 * I think the lead reads wonderfully with a few minor glitches:


 * "immense radiative output of active galactic nuclei and comparable astronomical objects" seems too technical. I don't think you can expect that random people will have heard of AGN's before or have any conception of what a "comparable object" would be.   It may also be difficult for many people to picture what "Immense radiative output" is.  How about "intense radiation pouring from the centers of certain galaxies"? The "pouring" is a little bodice-rippy for a scientific article, but it might awaken the reader's attention. ;) Willow 13:26, 18 July 2007 (UTC)
 * With "comparable objects" I mean microquasars and other stellar X-ray sources; if we can avoid the impression that we are talking about galactic scales only, we should do so. How about "Their strong gravity is thought to be responsible for the enormous amounts of highly energetic radiation emitted by certain types of astronomical objects (such as active galactic nuclei or microquasars)."?  With the parentheses indicating that this is more of a side remark? --Markus Poessel 13:43, 18 July 2007 (UTC)

That sounds good. :) For pithiness, how about shortening it to "...responsible for the intense radiation emitted by certain astronomical objects (...)."? Willow 13:50, 18 July 2007 (UTC)
 * Sounds better to me. Awadewit | talk  14:19, 18 July 2007 (UTC)
 * We have consensus, then? "Their strong gravity is thought to be responsible for the intense radiation emitted by certain types of astronomical objects (such as active galactic nuclei or microquasars)."? Markus Poessel 17:07, 18 July 2007 (UTC)
 * Yeay! OK, onwards and upwards. :) Willow 19:10, 18 July 2007 (UTC)
 * OK, change implemented; I've taken the liberty to strike out all the above to show we're finished with this. (I know that usually you only strike your own comments; I hope that in this small circle it is acceptable to speed things up). --Markus Poessel 06:38, 19 July 2007 (UTC)


 * I agree with Awadewit that we don't need to explain the Big Bang in the lead. People will have heard about it in the popular press, no? Willow 13:26, 18 July 2007 (UTC)
 * One concern is balance - I like the way that, at the moment, we have brief statements with at least some minor details for all the application areas. If we change to "General relativity is also the basis of the standard Big Bang model of cosmology" we're making the cosmology sentence shorter than all others; it's the only one without an explanatory note (most people will also have some idea about what a black hole is; still I think it's better to explain it, as we do now); also, we have the problem of wikilinking both to the physical cosmology or big bang page. --Markus Poessel 13:43, 18 July 2007 (UTC)
 * Sometimes elegant prose must be sacrificed. You can also shorten the others. :) They are a bit difficult as opening forays into the material, I think. Awadewit | talk  14:19, 18 July 2007 (UTC)
 * My concern was less for elegant prose, but more for the requirement that the lead should be a stand-alone mini version of the article (as opposed to just a teaser type of intro meant to suck the reader in). Without the brief explanations (and I would support adding something about gravitational waves, but perhaps in the last paragraph), I think it could not properly serve that need. Markus Poessel 17:26, 18 July 2007 (UTC)
 * I think I still agree with Awadewit. A reader has only so much brain power to give to an article, and we shouldn't tax them with tangential stuff in the lead.  The interested reader will pursue the nature of the Big Bang in the main article.  Maybe we should think of the lead as a "teaser movie trailer" showing the best parts of what's to follow. ;) Willow 19:13, 18 July 2007 (UTC)
 * As I said, it's not meant to be just a teaser. But I guess since people do know the Big Bang by name, it should be OK.  "General relativity is also the basis of the standard Big Bang model of cosmology."? --Markus Poessel 06:52, 19 July 2007 (UTC)
 * That sounds great to me! I guess we have consensus; yeay!  Willow 18:07, 19 July 2007 (UTC)
 * Striking out, then. --Markus Poessel 06:28, 20 July 2007 (UTC)


 * I would mention gravitational waves in the second paragraph, so that the reader is prepared to learn of the efforts to detect them in the third paragraph. Perhaps something like "General relativity also predicts other phenomena such as gravitational waves, which are disturbances in space-time geometry that move at the speed of light well-nigh independently of matter.  Although such waves have not been observed directly, there is good circumstantial evidence for them."? Willow 13:47, 18 July 2007 (UTC)
 * That goes on for too long for a lead. I don't expect to understand every term in a science lead. How about just "General relativity also predicts other phenomena such as gravitational waves"? We can learn later that they haven't been observed. You have only four paragraphs - is that essential to know? Awadewit | talk  14:19, 18 July 2007 (UTC)
 * That's possible, but I agree with Markus that we should explain somehow that GR goes beyond just "fixing" Newton's law of gravitation, so that the motions of matter and light are predicted accurately. A key step of GR beyond Newton lies in its making space and time "players" in their own right, capable of carrying waves with no matter around.  I'm not sure how to get that point across, though. Willow 19:20, 18 July 2007 (UTC)
 * I would have liked to include a brief description for gravitational waves, but I'm ready to settle for their mention in our new draft of the new Newton-Einstein-sentence (below? above? loosing track). --Markus Poessel 16:52, 19 July 2007 (UTC)
 * We might have consensus here, too. :)  Let's settle as Markus says and move on. Willow 18:07, 19 July 2007 (UTC)
 * Striking. --Markus Poessel 06:28, 20 July 2007 (UTC)


 * The lead image caption can be changed however you like. I like giving more information, but perhaps it was too much.  Willow 13:47, 18 July 2007 (UTC)
 * Let's see if we can find the briefest version that is OK with Awadewit. How about "Artists impression of the Cassini space probe's precision tests of general relativity: warped space (blue lines) and its effects on radio signals (green line) sent from Earth to the probe and back." --Markus Poessel 14:02, 18 July 2007 (UTC)
 * If you want to explain more, change the picture and move this one somewhere else. This sentence is still difficult to parse (two "of's" in a row). It is also not terribly clear that the radio signals are being sent from Earth, by the time you get to that part of the sentence. How about something like this: "The Cassini space probe's precision tests of general relativity, showing how warped space (blue lines) affects radio signals (green lines) sent from Earth (Artist's impression)." (I don't know if there is more than one artist - I assumed one.) Awadewit | talk  14:19, 18 July 2007 (UTC)
 * Fun overlap: I am looking at Sir Isaac Newton's philosophy explain'd for the use of the ladies (1739). I love the eighteenth century. Their "scientific popularizations" are fascinating. :) Awadewit | talk  15:01, 18 July 2007 (UTC)
 * That does sound interesting. I still have Faraday on my reading list, and someday I'll try to track down a copy of the "Natural science for the common man" (not the exact title) series that reputedly had such a great influence on young Einstein. --Markus Poessel 15:50, 18 July 2007 (UTC)
 * There were even feminine, parlor microscopes for recreational use! Ok, I'll stop now. Awadewit | talk  15:55, 18 July 2007 (UTC)
 * *I'd really like this picture in the lead. It's pleasing on the eye, with the photo-realistic elements it has.  You reformulation sounds very good, except that I would like to keep "from Earth to the probe and back" for factual accuracy. --Markus Poessel 15:50, 18 July 2007 (UTC)
 * So something like this: "The Cassini probe's precision tests of general relativity, showing how warped space (blue lines) affects radio signals (green lines) bouncing back and forth from the Earth (artist's impression)."
 * In my ear at least, "back and forth from something", however slight the effort to infer what the other object is, sounds sub-optimal. Also, I think it's not really a  back and forth, but more like Earth-probe-Earth, record result; Earth-probe-Earth, record result.  How about "The Cassini probe's precision tests of general relativity: warped space (blue lines) affects radio signals (green lines) sent from the Earth to the probe and back (artist's impression)."? Markus Poessel 16:50, 18 July 2007 (UTC)
 * I agree that we should keep the picture in the lead, since it's vivid and captures the idea of curved space and experimental tests of Einstein's theory. For ease of reading, I might change the nouns to verb(s) in the caption: "The Cassini space probe tested general relativity rigorously, showing that radio signals between the Earth and the probe (green wave) were delayed by warped space (blue circles)."  Does that sounds OK?  The word "showing" might be a little strong, since other causes besides warped space have not been ruled out; but the alternative ("supporting its prediction that") is maybe too wordy and weak for the lead.  Sanity check: "Warped space" or "warped space-time"?  I wish we could avoid the misconception that the signal would be actually seen to "dip" downwards on its way to the Earth, but maybe that's too much to ask for in the lead.  Willow 19:39, 18 July 2007 (UTC)
 * I guess we can decide what the blue lines mean - if we say "space-time" (or "space and time", to not scare people off) that is indeed the whole effect. "Space" is only part, so we would have to be careful like in my earlier version not to suggest it's everything. BTW, it's not just blue circles, it's a (polar coordinate) grid.  "Rigorous tests" doesn't sound right - rigorosity implies perfection such as you only get in mathematics; a test cannot be anything more than precise (which always leaves room for improvement).  "between the Earth and the probe" sounds a bit as if those signals might be hovering there, stuck in the middle.  The "artist's impression" should definitely be in there somewhere.  That said: "High-precision test of general relativity by the Cassini space probe: radio signals sent between the Earth and the probe (green wave) are delayed by the warpage of space and time (blue lines)."? --Markus Poessel 07:02, 19 July 2007 (UTC)

I like it. Let's go with it (and move on). Awadewit | talk  07:06, 19 July 2007 (UTC)
 * Moving on; have struck out discussion (it's close enough to Willow's version that I'm assuming no objection; if I'm wrong, no offense intended, and we can re-open discussion anytime). -- Markus Poessel 14:00, 19 July 2007 (UTC)

Where Newton's theory of gravity states that masses attract each other via a gravitational force, general relativity posits that, instead, they warp the geometry of space and time around them; one of the resulting effects is gravitational attraction. The reason I'm pasting this and not Awadewit's kind rewording is that I think Awadewit's version lacked one thing that I am very keen on having included, namely the implication that gravitational attraction is only one effect (among others) of the warpage of space and time; the rewording also sounded as if "attraction" was somehow more general than "force". I see your point about the order (Newton-Einstein vs. Einstein-Newton). I think the order here is better as it was (Newton-Einstein), but I have tried to change my version a bit in order to make clearer that Newton's theory is not the main concern here - "Where..." hopefully serves better than "According to..." to make clear from the start that Newton's theory is only here as a foil for something else. Also, remember that this is not the first sentence; general relativity has been mentioned before, properly at the very beginning. --Markus Poessel 18:21, 18 July 2007 (UTC)
 * We still have the second (I think) sentence to reach consensus on. My last proposal was


 * Let's see whether we can find a compromise that combines the virtues of our individual sentences, a Pandora sentence. ;) It should explain that GR predicts other things besides gravitational attraction, and should put GR first and describe what it is before what it is not per Awadewit.  How about something slightly longer? Willow 20:00, 18 July 2007 (UTC)

According to general relativity, the observed gravitational attraction between masses results from those masses warping space and time around themselves. Previously, gravity had been described by Newton's law of universal gravitation as a force between masses, but careful experiments have shown that Einstein's theory is more accurate than Newton's. General relativity also predicts entirely new phenomena such as gravitational waves.


 * PS. "GR posits" seems a little too elevated for a cozy article, which is why I used the longer version "According to GR," Willow 20:08, 18 July 2007 (UTC)
 * I think your rephrasing does take us forward a bit step. Two questions: Can we explicitly say that the new phenomena follow directly from the force->warping transition?  And can we perhaps, encouraging two birds to leave with one stone, take care of the explanatory gravitational wave sentence at the same time? Small quibble "warp ...around themselves" is too close to "wrap ...around themselves", I think.  Next try:

According to general relativity, the observed gravitational attraction between masses results from those masses warping space and time in their vicinity. Previously, gravity had been described by Newton's law of universal gravitation as a force between masses, but careful experiments have shown that Einstein's theory is more accurate; it's novel concept of gravitation also predicts entirely new phenomena such as gravitational waves – minute "ripples in space", the gravitational analogue of light waves.


 * Can, perhaps, still be polished, but I've tried to keep it short. --Markus Poessel 07:19, 19 July 2007 (UTC)

According to general relativity, gravitational attraction results from masses warping nearby space and time. Previously, Newton's law of universal gravitation had described gravity as a force between masses, but experiments have shown that Einstein's theory of gravitation is more accurate and predicts new phenomena such as gravitational waves.


 * Shorter yet. I am the ignorant sentence slasher. (Please let me know if you don't want me to suggest rewordings. I can see why you wouldn't.) Awadewit | talk  07:46, 19 July 2007 (UTC)


 * Almost there. Please, do continue to suggest rewordings. They usually lead to improvements.  In this rewording, I would like to keep the "observed" gravitational attraction (it goes with the "vicinity"; either we go with the "attraction", then we need to talk about "warping space and time everywhere", which might be a bit confusing, or we keep the "observed", in which case the "vicinity" is all we care about) and stress the "interesting" new (not everything new is good; in this case, new is good.  Next proposal:

According to general relativity, the observed gravitational attraction between masses results from those masses warping nearby space and time. Previously, Newton's law of universal gravitation had described gravity as a force between masses, but experiments have shown that Einstein's theory of gravitation is more accurate; what is more, it predicts interesting new phenomena such as gravitational waves.


 * I noticed you got rid of my gravitational wave description, too. I sympathize with your aim of keeping the lead brief, but I'm worried about its capacity to act as a "stand-alone" introduction. --Markus Poessel 13:54, 19 July 2007 (UTC)


 * I wouldn't worry about the summary part. You just need to briefly mention the important topics from the article in the lead, in proportion to their coverage in the article. I think mentioning gravitational waves is enough. The other function of the lead is to explain general relativity in four paragraphs. Many users only read the lead - that is what I do when I click from other articles for more information; say I was in the middle of a "history of physics" article and clicked on this page - would I read the entire thing? Probably not - I would only read the lead and then go back to "history of physics". You might think about it that way. Anyway, even though I think that "masses" repeats unnecessarily in this version, let's go with it. Perhaps inspiration will strike someone later. We need to move beyond the lead into the nitty-gritty. Awadewit | talk  14:14, 19 July 2007 (UTC)


 * OK, sounds reasonable. I'll just wait for Willow to give her OK (I don't want to go over her head), then implement the change. Thank you for your admirable patience, by the way - after all the time you already spent on the first review, I greatly appreciate that you're taking the time for what is effectively a second one (if not more).  I think your input (and arbitration) is essential here; my hope is that it will become less time-consuming as we move from the lead into the main text. Going by what's been happening so far, I think it's definitely worth it, but I'm sorry that, for the past days, you probably had more hassle and less Paine in your life than I assume you had been planning on.--Markus Poessel 15:09, 19 July 2007 (UTC)


 * We should wait, I agree. I'm glad that you think I'm being helpful in some tiny way. I really feel completely at sea here; I finally gave up worrying that everything I posted would sound totally idiotic. You can be proud that this article has convinced me to learn about tensors, vectors and the like. My roommate has been trying to do that for a while now. (I hope to return to Paine soon - I have great affection for The Age of Reason, so I want the article to be good. The time away is probably a benefit.) Awadewit | talk  15:40, 19 July 2007 (UTC)
 * Just to clarify, I didn't use "your input is essential" as a lesser known synonym for "you're being helpful in a tiny way". Without you or a test reader with comparable background, this discussion wouldn't work a quarter as well as it does.  So please, don't learn about tensors and vectors just yet (if you do, with an eye toward gr, I recommend reading Rindler's "Relativity. Special, general, and cosmological").  We need your unspoilt, non-technical point-of-view on this. Your good eye for formulations and experience in teaching how to write helps as well, of course.  --Markus Poessel 16:16, 19 July 2007 (UTC)

(undent) I think this is probably the first time I have seen a teacher tell someone "no no don't learn that just yet. You quest for knowledge would be detrimental to my work" :)--Cronholm144 16:26, 19 July 2007 (UTC)


 * Thanks; I really do feel like a broken record - "it's still too complicated". I will take a vow of chastity in regards to vectors and tensors, then. :) (Thanks for the recommendation - I will check it out from the library after the FAC.  By the way, I have now moved from "Newton for Ladies" to "Newton for children" - The Newtonian System of Philosophy (a.k.a. The Philosophy of Tops and Balls) by Tom Telescope.   Awadewit |  talk  17:22, 19 July 2007 (UTC)


 * The final version reads great to me, too! One worry, though: will readers understand that the final "it" refers to Einstein's theory?  I think that they will understand and I suspect that any cure (e.g., "general relativity") would make the writing more clunky (see below); but I thought I should at least raise the issue.  Please choose whatever version you like and put it in the article with my blessing. Let me just say, too, that Markus' patience on these fine details reflects a fine nature within. :) Willow 18:07, 19 July 2007 (UTC)

According to general relativity, the observed gravitational attraction between masses results from those masses warping nearby space and time. Previously, Newton's law of universal gravitation had described gravity as a force between masses, but experiments have shown that Einstein's theory of gravitation is more accurate. What is more, general relativity predicts interesting new phenomena such as gravitational waves.


 * Motion carried, then. --Markus Poessel 06:34, 20 July 2007 (UTC)


 * Opening the next section for discussion. I prefer small steps, i.e. really going subsection by subsection.  If it turns out that we need to go back later to some earlier subsection, we can do so; I just want to keep the focus narrow, and limit the number of discussions going on in parallel. --Markus Poessel 06:58, 20 July 2007 (UTC)