Talk:Shapiro delay
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[edit] Removed text
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)
True. Kmarinas86 23:22, 8 November 2005 (UTC)
False: This argument has not been discredited, claims alluding to it's refute have been asserted by mainstream Astronomers with an agenda to prevent the immenent loss of their funding. The only force stronger than the force of gravity, is the force of greed. Denying clear evidence is a sure sign of religious bias, and a spit in the face of empirical science. unsigned 23:18, 7 November 2006 (UTC)
I submit that the above be ignored. The Shapiro delay cannot explain Hubble flow: it is very much too small. This is not a matter of something being discredited, but of it never being considered seriously in the first place. I suspect that 'unsigned' would call me "mainstream Astronomer", but making a statement on this one way or the other is most unlikely to affect anyone's funding, assuming that they support it. Michaelbusch 22:48, 6 November 2006 (UTC)
I submit that no evidence be ignored, open discussion and research is the way to get at the truth, not by censoring opinions that don't agree with one's own. The Shapiro effect is not too small when applied to photons traveling over vast distances, such as through interstellar space. the cumulative effect would account for observed redshift on the Hubble scale. incidentally the Mössbauer effect and Compton effect have also been proposed as alternative causes for redshift [citation needed] . As for funding, no Astrophysicist who has published and built his reputation around such research, having acquired government funding involving "astronomical" sums of money is going to drop his basket of eggs to chase a rainbow, that may or may not hold the key to the true nature of the cosmos. unsigned 23:22, 7 November 2006 (UTC)
I did not censor, merely suggesting that your previous comment isn't relevant to the article. I simply gave the reason for Shapiro delay not being relevant on the cosmological scale: there is very much less mass. Mossbauer fails because it works only for solid materials and for gamma rays. Compton fails because it doesn't work at low energies. This is all I will say on the subject, because this is an encyclopedia, not a pseudo-science discussion board. Michaelbusch 00:05, 7 November 2006 (UTC)
How much mass there is, or isn't is a matter of distance, the Hubble scale assumes a given distance to redshift ratio, however there is no guarantee this ratio is correct. With gravitational drag the greater the distance light travels, the greater the redshift. This would explain why light from galaxies beyond 7 x 10^9 lightyears is unable to reach us. There may be an absolute maximum distance light can travel before it's wavelengths are time stretched beyond what earth based telescopes can detect.
To state that a comment on the Shapiro delay accounting for stellar redshift is irrelevant to an article on Shapiro delay is a bit like saying the pope is irrelvant to the vatican. this is not pseudo science. Furthermore, neither you, nor I nor any living human is an authority on the true nature of the cosmos, and any claim on such absolute knowledge is a pretence. All theories are by definition "theoretical" and chances are we're all way off. you may have the last word on this discussion board, but your's is not the last word on the subject. unsigned 23:37, 7 November 2006 (UTC)
At the penalty of contradicting myself, one final statement on this thread: Shapiro delay as described in this article does not change the frequency of light at all, just changing the travel time. There are corrections to frequency which are related to gravitational Doppler shift, but those are very small indeed. Michaelbusch 00:22, 7 November 2006 (UTC)
The frequency of light need not change to produce redshift in a time dragged frame, the reciprocal of frequency is wavelength, and it's the wavelength which would be stretched. It's necessary to look at the big picture, rather than nitpick over it's small components. There is also no guarantee that the GR model of gravity is correct, for example in a plasma universe governed solely by electrodynamic laws, the physics on a cosmic scale is not the same.
note: no accusation is made towards any particular Astronomer regarding their motives, undoubtedly there are very many mainstream Astronomers who are absolutely sincere and engaged in honest research, my comment was only directed at those (who know who they are) who do in fact have an agenda. unsigned 23:49, 7 November 2006 (UTC)
[edit] Missing data on Shapiro effect
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)
I would suggest writing Prof. Shapiro directly. here is his email address at the Center for Astrophysics - Harvard Smithsonian Astrophysical Observatory: ishapiro@cfa
[edit] Some problems with current version
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)
Also, the last subsection is particularly bad in terms of failing to explain that this stuff (e.g. energy, momentum of photon, or better yet, of laser pulse) is observer dependent. ---CH 04:44, 19 December 2005 (UTC)
[edit] Page name
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)
- 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)
[edit] Time delay and collapsing objects
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)
[edit] The Formula was wrong
It was obviously wrong as it gave a negative delta t for not too large angles between the source and the mass. I've changed the definition of the unit vectors into what I remember to be correct, but this needs to be checked. Count Iblis 15:11, 20 August 2006 (UTC)
