tag:blogger.com,1999:blog-22973357.post8889728351138145462..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: Messenger, Mercury, and General RelativitySabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger22125tag:blogger.com,1999:blog-22973357.post-66817690599131915422008-02-18T05:02:00.000-05:002008-02-18T05:02:00.000-05:00Hi changcho,yes, professional bloggers are faster ...Hi changcho,<BR/><BR/>yes, professional bloggers are faster ;-)... The reader Emily is mentioning who asked the question was indeed me, and I've got the same mail from KinetX' Tom Taylor, but haven't condensed that yet in a blog post... my version will follow over the week...<BR/><BR/>Best, Stefanstefanhttps://www.blogger.com/profile/09495628046446378453noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-20126322569485483782008-02-18T01:16:00.000-05:002008-02-18T01:16:00.000-05:00Hi, just to revisit this one more time: E. Lakdaw...Hi, just to revisit this one more time: E. Lakdawalla of the Planetary Society goes into this and actually got quantitative information from the people doing the navigation for MESSENGER (KinetX) - they use the JPL software.<BR/><BR/>Check out her excellent post <A HREF="http://www.planetary.org/blog/article/00001329/" REL="nofollow"> here </A>Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-560945403984108842008-02-05T19:06:00.000-05:002008-02-05T19:06:00.000-05:00Stefan - more about GR and its effects on orbits.I...Stefan - more about GR and its effects on orbits.<BR/><BR/>In 2006, J. Williams of JPL gave the <A HREF="http://dda.harvard.edu/brouwer_award/BrouwerAward_2006_Williams.pdf" REL="nofollow">Brower award lecture</A> at the AAS's Division of Dynamical Astronomy (DDA) meeting; the topic was lunar laser ranging. <BR/><BR/><BR/><BR/>Regarding the topic of your post, the main point (see his p. slide 21)Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-32373364603775656392008-02-05T18:35:00.000-05:002008-02-05T18:35:00.000-05:00Stefan,"Information released in 2006 by the GALILE...Stefan,<BR/><BR/>"Information released in 2006 by the GALILEO project states that relativistic corrections will be the responsibility of the users (that is, the receivers)."<BR/><BR/>Interesting, however I beleive the reason for this is that they will be the only ones to be able to supply the proper correction information to the users. This I beleive is tied in with their intending to charge forPhil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-54910240842165604662008-02-05T16:47:00.000-05:002008-02-05T16:47:00.000-05:00Dear Bee,thanks for the pointer! Section 12 of Nei...Dear Bee,<BR/><BR/>thanks for the pointer! <BR/><BR/><A HREF="http://relativity.livingreviews.org/open?pubNo=lrr-2003-1&page=articlese12.html" REL="nofollow">Section 12 of Neil Ashby's paper</A>, on Global Navigation Systems, has a curious statement about the future European Galileo Navigation System: <BR/><BR/><I>Information released in 2006 by the GALILEO project states that relativistic stefanhttps://www.blogger.com/profile/09495628046446378453noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-2707277228806598412008-02-05T15:03:00.000-05:002008-02-05T15:03:00.000-05:00Michael:http://relativity.livingreviews.org/Articl...Michael:<BR/><BR/>http://relativity.livingreviews.org/Articles/lrr-2003-1/Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-73201091903584216502008-02-05T14:58:00.000-05:002008-02-05T14:58:00.000-05:00Interesting post.I heard that GPS calculations als...Interesting post.<BR/>I heard that GPS calculations also take in account GR. Does anyone know if that is true?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-69527465098913514962008-02-01T23:42:00.000-05:002008-02-01T23:42:00.000-05:00Hi Stefan,“Auch das Beatles”As perhaps related inf...Hi Stefan,<BR/><BR/>“Auch das Beatles”<BR/><BR/>As perhaps related information <A HREF="http://thelede.blogs.nytimes.com/2008/02/01/nasa-says-hello-universe-meet-the-beatles/?hp" REL="nofollow">NASA announced</A> today that they will be celebrating their 50th anniversary of its first deep space mission (explorer 1) with an attempt to call the ETs, well actually more like serenade them. On this Phil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-43325921586909660012008-02-01T12:50:00.000-05:002008-02-01T12:50:00.000-05:00Hi Vagelford, changcho,the eccentricity of the cir...Hi Vagelford, changcho,<BR/><BR/><I>the eccentricity of the circle is e=0.</I><BR/><BR/>oops, of course, that is true - I have corrected the error, and changed the original text from the wrong version "for a circle, e = 1, and the smaller e, the more elongated the ellipse"...<BR/><BR/>Thank you very much for your careful reading :-), and sorry if I have confused some readers with the mistake. <BRstefanhttps://www.blogger.com/profile/09495628046446378453noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-89845332977839369922008-02-01T12:38:00.000-05:002008-02-01T12:38:00.000-05:00"for a circle, e = 1, and the smaller e, the more ..."for a circle, e = 1, and the smaller e, the more elongated the ellipse"<BR/><BR/>Vagelford, right, this should read<BR/><BR/>"for a circle, e = 0, and the bigger e, the more elongated the ellipse"<BR/><BR/>Minor error, rest of the post is very good.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-73651141561234249652008-02-01T07:16:00.000-05:002008-02-01T07:16:00.000-05:00Very nice post. These simple results illustrate bo...Very nice post. These simple results illustrate both interesting physics and its "every-day" applications.<BR/>One small point though, the eccentricity of the circle is e=0.Vagelfordhttps://www.blogger.com/profile/16733686685163784134noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-45851387429463826672008-02-01T06:56:00.000-05:002008-02-01T06:56:00.000-05:00Hi Stefan,“actually, the first one was the sheet o...Hi Stefan,<BR/><BR/>“actually, the first one was the sheet of paper with the address label that comes with the Scientific American ;-)”<BR/><BR/>I get the same thing with Discover magazine. Show’s one the practical difference between the two<BR/><BR/>“Then, one could have argued that neglecting General Relativity results in a high risk to have an impact instead of a flyby, something that is Phil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-58407055315856594672008-01-31T22:18:00.000-05:002008-01-31T22:18:00.000-05:00Hi Stefan, another great interesting post. I wonde...Hi Stefan, another great interesting post. I wonder what the consequence of Newton's actual predictions?..ie where would one end up in relation to actual going to Mercury?<BR/><BR/>Where one ends up via Newton, and where one ends up via Einstein, if one uses a "google-earth", google-mercury type camera? Comparing the differing photographic evidence would be fascinating, the difference of maybe Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-62539244758384680312008-01-31T17:00:00.000-05:002008-01-31T17:00:00.000-05:00Hi changcho,So, the take-home-message is an error ...Hi changcho,<BR/><BR/><I>So, the take-home-message is an error of a few kilometers by not taking into account GR effects due to the Sun.</I><BR/><BR/>Yes ...unless I have made some stupid mistake ;-). <BR/><BR/>But it's of course perfectly in line with the Schwarzschild radius argument you had mentioned before - depending on the length of the free-fall trajectory, the difference between a stefanhttps://www.blogger.com/profile/09495628046446378453noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-49962979530397052282008-01-31T16:39:00.000-05:002008-01-31T16:39:00.000-05:00Hi Phil,tell me where you buy your envelopes actua...Hi Phil,<BR/><BR/><BR/><I>tell me where you buy your envelopes </I><BR/><BR/>actually, the frist one was the sheet of paper with the address label that comes with the Scientific American ;-)<BR/><BR/><I>... serves as an example of how GR really counts as being practical and relevant.</I><BR/><BR/>Well, I am not convinced if Messenger is a good example. After all, Newton does the driving, with stefanhttps://www.blogger.com/profile/09495628046446378453noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-35390015711214644622008-01-31T16:38:00.000-05:002008-01-31T16:38:00.000-05:00Hi Stefan - nice back of the envelope computations...Hi Stefan - nice back of the envelope computations, thanks! So, the take-home-message is an error of a few kilometers by not taking into account GR effects due to the Sun.<BR/><BR/>The long equation you show is the same (in a slightly different format) that I have from JPL technical memo 33-451, but the equation itself is referenced to "Moyer, T. D. JPL internal document Jan. 4, 1968".<BR/><BR/>Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-51973545314485195272008-01-31T13:21:00.000-05:002008-01-31T13:21:00.000-05:00Also, re Ken Nordtvedt: he wrote a much and wrongl...Also, re Ken Nordtvedt: he wrote a much and wrongly IMHO forgotten paper (K. Nordtvedt, “The equivalence principle and the question of weight,” Am. J. Phys. 43 (3), 256-257 (1975) about how gravitational fields reduce the apparent weight of objects suspended by long cables. It is like a red or blue shift for weight. IOW, let's say I have an elephant held by a long cable suspended in a Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-57024939177919795942008-01-31T12:39:00.000-05:002008-01-31T12:39:00.000-05:00OK, about Mercury first let me repeat the followin...OK, about Mercury first let me repeat the following cute Halloween pictures link:<BR/><BR/>My girlfriend and I went to a Halloween party as Venus and Mercury, complete with toga and put-up hair, winged golden helmet and sandals, etc. I have to say, she can get away with playing Venus! Go to <A HREF="http://www.tidewater.us.mensa.org/Graphics/Halloween2006/index.html" REL="nofollow">Link.</A><BR/>Neil Bateshttps://www.blogger.com/profile/04564859009749481136noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-80932603984733548272008-01-31T12:28:00.000-05:002008-01-31T12:28:00.000-05:00On a less elegant plane... how is the space probe ...On a less elegant plane... how is the space probe kept cool when it is so close to the sun? Add deep UV and solar wind to have a nighmare material survival environment.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-42823619422018962982008-01-31T11:50:00.000-05:002008-01-31T11:50:00.000-05:00You demonstrated the power of a sound physics educ...You demonstrated the power of a sound physics education. Suitably armed, one can pose a simple question, find the appropriate context to answer it, then turn the crank. No appeal to authorities required. <BR/><BR/>Really great post! Thanks.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-30108579383720007252008-01-31T08:31:00.000-05:002008-01-31T08:31:00.000-05:00Hi Stefan,Just a follow up to the earlier comments...Hi Stefan,<BR/><BR/>Just a follow up to the earlier comments I made about the importance of making GR relevant to the public at large and how that might be done. These articles you have written and the related discussion is as I have said serves as an example of how GR really counts as being practical and relevant. When thinking about this I remembered another such example that was resultant of Phil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-51765242328242612722008-01-30T23:42:00.000-05:002008-01-30T23:42:00.000-05:00Hi Stefan,“I realised that a simple back-of-the-en...Hi Stefan,<BR/><BR/>“I realised that a simple back-of-the-envelope calculations already yields a good estimate for the influence of General Relativity on the space probe.”<BR/><BR/>Stefan, you have to tell me where you buy your envelopes for I simply must have some of those:-)<BR/><BR/>Seriously though it’s great that you took this a step further by demonstrating what’s involved and actually Phil Warnellhttps://www.blogger.com/profile/15671311338712852659noreply@blogger.com