Talk:Shapiro time delay

message: I removed this text: Some have argued that the Shapiro Effect can account for the Hubble redshift without having to posit an expanding universe. It appears this has been thoroughly discredited. P. Riis 17:13, 21 Oct 2004 (UTC)
thread_title:  Removed text 

message: If someone knows the numerical data it would be nice to place them here on the page. How much longer it takes the signal to make the round trip and how much speed of light changes in the gravitational field. My theoretical result (from the principle of conservation of energy) tells that dc/dx=g/(2c), where x is in directon opposite to the source of gravitational field. I wonder what's the observational result in the Shapiro effect. Jim 18:58, 2 September 2005 (UTC)
thread_title: Missing data on Shapiro effect

message: Quick note: one problem is that "isolated mass" should be "nonrotating isolated mass" and should include discussion of the coordinate chart.  The Schwarzschild exterior chart is a good choice here, but of course other charts are more useful for other purposes, and reader should not be confused by conflating a chart with the solution it describes, particularly since Schwarzschild charts are often useful for other static spherically symmetric solutions, such as Reissner-Nordstrom or Janis-Newman-Winacour.---CH 04:41, 19 December 2005 (UTC)
thread_title: Some problems with current version

message: Page moved from Shapiro effect to Shapiro delay per a request on WP:RM. Search on Google Scholar shows the latter term is preferred in academic circles (more strongly than on Google, though there too). Rd232 talk 12:31, 27 December 2005 (UTC)
replies: text: Thanks, Rd232!  In fact, Shapiro time delay is the most precise short term which is in standard use, so I
had planned to make that change but hadn't gotten to it.  But Shapiro delay is probably good enough. ---CH 15:25, 24 January 2006 (UTC)
thread_title:  Page name 

message: Whoever wrote that was apparently confusing the Shapiro time delay effect with gravitational redshift in an expanding null congruence from a spherically symmetric gravitating object, apparently even confusing freely propagating light with signals from the interior of a collapsing fluid ball.  If that person is upset that I removed the section, I ask that he/she at least study D'Inverno's textbook (which should clarify these points) before trying again.  TIA!
This article is still badly in need to a thorough rewrite to improve accuracy, emphasis, and readability, (but still not very on my long personal to do list, unfortunately). ---CH 15:25, 24 January 2006 (UTC)
thread_title:  Time delay and collapsing objects 

message: It could be helpful if someone would draw a sketch with the emitter the receiver and the interfering plantet with vectors and such.Agge1000 06:34, 15 November 2007 (UTC)
thread_title: Graphical Representation

message: Gravitational time dilation is a function of gravitational potential, not of gravitational field strength.  Since the delay can be viewed as an effect of time dilation, it too is a function of potential and not field.  The article as currently written is confusing on this point, and should be clarified. Howard Landman (talk) 14:56, 25 December 2012 (UTC)
thread_title:  Potential versus field 

message: This page had a quotation from an article by Shapiro that did not appear in the article cited. That quotation was replaced with the closest matching sentences from the article.  — Preceding unsigned comment added by PaunchyCyclops (talk • contribs) 17:59, 30 December 2014 (UTC)
thread_title:  Fabricated quotation 

message: I've added a citation-needed tag for the equation for the delay, \Delta t -- I don't think the expression given can be correct (since it indicates that when R and x are orthogonal -- that is, when the source and the mass are at right angles from the point of view of the observer -- the delay is zero, which won't be the case).  I'm loth to change this myself, however, because it may just be that the explanation for the symbols has become garbled (what's there seems ... dubious), and it would be best for the original author of this text to fix it. NormanGray (talk) 22:30, 23 February 2015 (UTC)
thread_title:  Garbled equation? 

message: "moderate strength (say, of stars and planets, but not one of a black hole or close binary system of neutron stars)"... the predictions of Relativity are not subject to this limitation. Either this assertion needs to be justified or removed. The stretching of space between two points due to mass is proportional to the difference in potential energy of the two points. That's it.  — Preceding unsigned comment added by McGinnis (talk • contribs) 01:38, 12 June 2016 (UTC)
replies: text:  I think whoever wrote the article did a good job, considering there is confusion even in the advanced literature on these topics. You say, "light does NOT travel more slowly." While it is true that the proper velocity of light, as measured locally along its path, is constant, the coordinate velocity of light is less than c in a gravitational well. For example, dr/dt<c for a photon emitted radially from a star. This coordinate velocity would be the velocity as judged from infinity. Hence the confusion. Indeed, the Shapiro quote at the top of the article says, "Because, according to the general theory, the speed of a light wave depends on the strength of the gravitational potential along its path . . . " so Shapiro himself said the speed of a light wave depends on potential, and hence varies. Shapiro no doubt meant coordinate speed. Please see section below entitled Is the Shapiro delay due to time dilation or path length increase? Very often in GR, there are multiple "correct interpretations", but we must specify with precise accuracy the meaning of every term we use. 71.32.47.71 (talk) 20:00, 26 December 2018 (UTC)
thread_title:  Please justify this assertion 

message: If the Shapiro Delay is to be interpreted in relativistic terms then the delay can only be interpreted as a lengthening of path. In Relativity, path length is ct where t is the time it takes light to traverse the path. If you want to interpret it as light slowing down, you aren't using Relativity. The reason spacetime is curved in a gravitational field is that it is dilated. As Shapiro shows, the path length is increased.
Is this page going to receive review or do I need to rewrite it?
Michael McGinnis (talk) 02:10, 30 July 2017 (UTC)
replies: text:  You say, "If the Shapiro Delay is to be interpreted in relativistic terms then the delay can only be interpreted as a lengthening of path." This is inaccurate. Time dilation and path length increase contribute roughly equally. Please see section below entitled "Is the Shapiro delay due to time dilation or path length increase?" 71.32.47.71 (talk) 13:40, 27 December 2018 (UTC)
thread_title:  Why not use a Relativistic explanation? 

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thread_title:  External links modified (January 2018) 

message: The beginning of the article states, "The time delay is caused by spacetime dilation, which increases the path length." The term spacetime dilation, although accurate, may be unclear (I've never seen it before). Also, the increase in path length is only a partial cause of the delay. The statement would more accurately read: "The Shapiro time delay is caused both by gravitational time dilation and by a relativistic increase in path length." The contributions are roughly equal. This can be seen from the coordinate speed of light in the Schwarzschild metric, which is dx/dt = √(-g00/grr). To obtain travel time t, one solves this for dt and integrates over the path x, where the path is approximated as straight. The fact that g00, which represents the time dilation factor, and grr, which represents the path length factor, are both present means they both contribute. This is clearly laid out in the textbook Gravitation and Inertia by Ignazio Ciufolini and John Archibald Wheeler (Princeton Series in Physics, 1995), pp122-125  71.32.47.71 (talk) 20:35, 26 December 2018 (UTC)
thread_title:  Is the Shapiro delay due to time dilation or path length increase? 

message: The time delay can be split into two different parts:
1) The Shapiro time delay, caused by a variation in the speed of a photon if it is submerged in a gravitational potential.
2) The geometric delay, caused by the increased length of the total light path from the source to the target, which is due to gravitational deflection.
This article focuses primarily on Shapiro time delay and tries to downplay the relevance of geometric delay. It states that: "the contribution from the change in path, being of second order in M, is negligible". The straight path approximation is actually incorrect in the first order.  — Preceding unsigned comment added by 2001:1C00:F20:8100:45EF:C2D7:33F9:FF75 (talk) 13:07, 19 November 2019 (UTC)
thread_title:  The straight path approximation is incorrect in the first order 

message: Elena V. Pitjeva:Tests of General Relativity from observations of planets and spacecraft is no longer available but at Springer https://link.springer.com/article/10.1134/1.1922533 Ra-raisch (talk) 20:22, 6 October 2020 (UTC)
thread_title:  Ref.4 

message: Interesting article, but in the Shapiro time delay equation, in the last term of the right hand side, the capital O function should be defined or named. I don't think we mean the Little-O or the Big-O functions. Since here the argument to the O function depends on the small constant (G^2/c^6), the + capital O function perhaps means 'plus a small remainder term that depends on': ((G^2/c^6)*M^2)  ? 
Thanks (Eromana (talk) 21:55, 14 October 2020 (UTC)
replies: text: This of course is the Landau symbol of order of error Big_O_notation. Ra-raisch (talk) 09:47, 2 September 2021 (UTC)
thread_title:  Capital ''O'' function definition