Talk:Proper time

message: I have corrected some spelling, and I have changed some headings. The wikipedia Manual of style 
recommends:  Avoid links within headings.
--Cleon Teunissen | Talk 14:57, 16 May 2005 (UTC)
thread_title:  Corrected some spelling 

message: "Joke" -  I decided to change "line integral" back to "path integral" primarily becuase your change left the article inconsistent both internally and with Wikipedia itself.  Internally, there are several references to the path integral in this article, but you only changed one.  Also, in Wikipedia, the title of the article is "path integral", not "line integral" (although it does acknowledge line integral as being synonomous with path integral).
If you feel strongly enough on this matter you may change the wording again.  All that I ask is that this time you change all occurances of the term "path integral" instead of just one.
--EMS | Talk 17:53, 29 May 2005 (UTC)
replies: text: Oh, I didn't notice that it was in multiple places in the article. It's not a big deal, it's just that physicists call functional integrals path integrals. --Joke137 21:06, 1 Jun 2005 (UTC)
replies: text:  I am aware of Feynman diagrams but not of the intergration being called a "path integral" also.  So I now see what my usage is jarring to you.  As I wrote above, my big complaint is the loss of consistency instead of the change of terminology.  I do not revert edits without a good reason to do so, and would not have reverted yours if the change had been done throughout the article. --EMS | Talk 22:11, 1 Jun 2005 (UTC)
thread_title:  "Path integral" vs. "line integral" 

message: The last equation seems to be missing a 'dt' at the end; could someone who knows how to edit the equations fix it?  Thanks! Fasrad 13:57, 16 October 2006 (UTC)
replies: text: Done.  Thanks for noticing it. --EMS | Talk 14:30, 16 October 2006 (UTC)
thread_title:  Minor typo in equation? 

message: I've rewritten the verbal definition in the introduction to stress how proper time differs from coordinate time. I've also brought the mathematical definition for SR ahead of the GR definition. Most readers of this article are likely to be learning SR and won't be familiar with GR, index notation, summation conventions and metric tensors. 
I think a little further copy-editing may be required to make the whole article flow consistently. I plan to modify the article on coordinate time later.--Dr Greg 13:20, 12 December 2006 (UTC)
thread_title:  Restructuring 

message: I see there are two past discussions of this topic, but I'd like to open a new one since the prior ones seem to be complete conversations. I think it is highly inappropriate to consider proper time for lightlike intervals. The first sentence of the article,  
"In relativity, proper time along a timelike (or lightlike) world line is defined as the time as measured by a clock following that line."  
is 100% incorrect. In relativity, it is impossible that such a clock can exist on a lightlike trajectory. The spacetime interval which can be linked to proper time for timelike intervals, but not necessarily so, is identically zero for lightlike trajectories. In addition, the footnote on Landau and Lifshitz's text "Yet others aren't clear on whether lightlike intervals are included" is also incorrect as L&L make abundantly clear in the beginning of the section that they are considering a reference frame which travels on the trajectory. Light cannot, I repeat cannot have such a trajectory. Further still, on page 245 of the same text, L&L correctly point out that,  
"The equation of a geodesic in the form [involving the spacetime interval] is not applicable to the propagation of a light signal, since along the world like of the propagation of a light ray the interval ds, as we know, is zero, so that all the terms in [the geodesic equation] become infinite."  
L&L go on further that to define null trajectories in a purely geometrical context which while resulting in the same form as the original geodesic equation does not invoke the notion of time in any way shape of form. Other references can be supplied to support this, this is not controversial in the physics community except among those who do not fully understand the theory. Simply put, lightlike intervals are not included. The other reference, Lawden on page 116 make the same statements as L&L,  
"The definition of a geodesic which has been given at the beginning of this section cannot be applied to the class of curves for which the interval ds between adjacent points vanishes."  
Thus the other footnote, "Some authors include lightlike intervals in the definition" is also completely incorrect and results from a incomplete reading of Lawden's page 150 who relates the trajectory to the observer's coordinates. To make this as absolutely clear as possible: The lightlike/null trajectory is not in any way associated with a concept of proper time and must be parameterized in a completely separate context. I am going to remove the parenthetical inserts involving lightlike trajectories in this article's discussion of proper time and correct the footnotes as I've explained above. Those who disagree, please reply on this talk page. 150.135.210.29 (talk) 07:29, 5 December 2015 (UTC)
replies: text: I've made the edits and added several additional references and footnotes, as well as a short statement on when and when not the mathematical procedure of the article is mathematically and physically valid. 150.135.210.29 (talk) 09:15, 5 December 2015 (UTC)

text: Edit, I did a rereading of Lawden. (Specifically section 7 p.17, https://archive.org/details/AnIntroductionToTensorCalculusRelativity) The original footnote is not incorrect as I first accessed, this author generalizes proper time to be synonymous with space time interval even goings as far as to label even proper distances as 'imaginary proper times'. This generalized definition of perfectly consistent, but would imply that the proper distance and proper time articles should be merged. I believe the reader is better served if the two notions are kept separate and proper time left to its restricted form involving a measurable quantity constructed from a reference frame as seen in the derivation of this article. 150.135.210.29 (talk) 10:19, 5 December 2015 (UTC)
replies: text: I agree with your entire analysis and edits. Good job. However, your most recent edits () include some slight non-neutrality as wp:OR: eventhough it is just in a footnote, the phrase "... but this comes at the cost of also including the spacelike proper distances" is not in the source. I have rephrased that into "... and also include the spacelike proper distances as imaginary proper times". - DVdm (talk) 11:19, 5 December 2015 (UTC)
replies: text: Might add that L&L also use imaginary intervals. They define the interval as  rather than  and on occasion mention imaginary intervals. YohanN7 (talk) 12:06, 5 December 2015 (UTC)
replies: text: Thanks for the fix DVdm. To YohanN7, this is the sign convention issue raising its ugly head. L&L uses (+---), so imaginary intervals are spacelike and real intervals are timelike. In the (---+) convention such as used by Lawden and others, the vice versa is the case. 150.135.210.29 (talk) 00:34, 6 December 2015 (UTC)
replies: text: Yes, of course. By the way, it was originally my personal blooper to include the L&L ref as being "undecided" when it came to light-like intervals. I took it from memory that turned out to be faulty, and then I never returned to the issue. The other references weren't available to me. Thanks for fixing this. YohanN7 (talk) 10:38, 7 December 2015 (UTC)
thread_title:  Concerning proper time for lightlike intervals 

message: There doesn't appear to be any mention of difficulties or impossibility of measuring proper time in a frame of reference undergoing extreme acceleration.  Ref: http://iopscience.iop.org/article/10.1088/0264-9381/32/17/175003/meta;jsessionid=D5CC1EA3EE4769553387910B5BD41133.c1. Anyone up for the task?
RegulatorRectifier (talk) 18:29, 13 December 2015 (UTC)
replies: text: "Difficulties" not worth mentioning since proper time measure in 10^16 m/s² frame was done in the 70's, to a couple ppm. 2601:542:103:A1F0:8DAE:9D41:350A:DD10 (talk) 21:47, 1 August 2023 (UTC)
thread_title:  Effect Of Extreme Acceleration