Talk:Gravity Probe B

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[edit] FAX checksum problem

I only heard of this as an unsubstantiated rumor, so I removed it. Please give source, if you want to put it back in. Here is the official text Highlight April 19 why the launch was scrubbed. Awolf002 22:33, 20 Sep 2004 (UTC)

[edit] Science results?

Great mission review; are there any science results to report? Even an arxiv report? linas 00:25, 30 October 2005 (UTC)

Someone really should add write-up if there are any results, it is already end of 2005 and there is big silence. Maybe did they did not find the effect that was predicted? 195.70.48.242 14:28, 13 December 2005 (UTC)

We're all waiting for the results. I'm sure as soon as they are public, someone is going to add it all, here. Awolf002 14:35, 13 December 2005 (UTC)

Aww, come on, its been a year and a half, there's gotta be a preprint discussing at least preliminary results. linas 15:11, 13 December 2005 (UTC)

Well, they finished taking the calibration data set just three months ago. Also, they seem to have a good mechanism to keep "the lid" on all preliminary results. Patience, friends! Awolf002 18:21, 13 December 2005 (UTC)

Speaking as a former student intern on the project, who just visited there over Winter Break, I can say that the timeline for finishing data analysis is around the end of summer (2006). After that, it will be peer-reviewed, and hopefully released around the end of 2006. Grodin Tierce 19:27, 20 January 2006 (UTC)
Patience - The phase 2 they are working on at the moment (June 2006) is to get the monthly estimate of each gyro individually pointing with respect to the guide star. Phase 3 will correlate the gyro readings into a single estimate for the satellite. The *final* stage (predicted April 2007) is to reference the gyro motion to the stella background instead of the guide star coordinates they have been working in so far, by adding in the measured motion of the guide star. This motion measurement has been done by a completely different team, and was started years before the launch to improve the reliability of the measurement. This separation of the detailed gyro motion analysis and the guide star motion could be seen as quite an effective way of not only "blinding" the gyro analysis team to the "right answer", but demonstrating that they are so blinded. NeilUK 07:14, 11 June 2006 (UTC)
Let's just wait until the official announcment in April until we try to judge their results, which no one in the public has been informed of.--Planetary 16:56, 19 July 2006 (UTC)
keep on with the patience. April announcement will be interim results, more analysis through the rest of 2007 will improve the expected error marginNeilUK 09:14, 12 February 2007 (UTC)
More patience -- the final results are now expected in May 2008. I've updated the date on the page. BentSm (talk) 23:59, 16 December 2007 (UTC)
Even more patience the results are now not expected until September 2008, and possibly March 2010! Garthbarber (talk) 10:39, 25 March 2008 (UTC)

[edit] PROOF!!!

I seriously doubt that: "When the mission is successfully completed, GP-B will be the most precise attempt at verification of any effect predicted by general relativity." This would have to exceed the accuracy of timing which has been the most precicely defined SI unit there is for years. GR predicts the speed of light in a certain media and i think this number will stay unprecedented for quite a while.

So in light of these circumstances, could anyone verify the given sentence?Slicky 17:23, 28 March 2006 (UTC)

First: You should distinguish special relativity and general relativity. Second: The value of light speed in vacuum is not predicted by any theory, it's a convention given by SI definition of meter. Previously it was a measured value. Third: The special relativity theory says that the speed of light in vacuum is constant, but this is a postulate not a prediction. --Egg ✉ 22:22, 28 March 2006 (UTC)

[edit] GPS Satellites Beating GPB to the punch?

I read an article within the last few years suggesting that data from GPS satellites had already been used to verify directly the same that GBP is testing.

I can't find the article now. Anyone care to comment?

If technological change accelerates enouugh, we should expect to see this kind of thing a lot. We might stop planning any experiment that takes more than 3 years to perform, assuming things will be so different in 3 years, it's not worth the risk.

I also read that article. I remembered from it that GPS had to account for frame dragging in order for it to work, thus it indirectly proved that frame dragging exists. There was some controversy that the test was not necessary because of this. I think this subject deserves a "Controversy" section in the main article.


The article I think you're talking about is a Nature paper - I. Ciufolini and E. C. Pavlis, A confirmation of the general relativistic prediction of the Lense-Thirring effect, Nature 431, 958 (2004). However, its results seem to be far from accepted; see for example http://arxiv.org/abs/gr-qc/0410110. Going into the detail without overwhelming the entry with technical stuff would be tricky; a reference on the page for frame-dragging might be appropriate, though. Chrislintott 09:47, 8 February 2007 (UTC)

[edit] dates

Is there some reason to state the mission runs from 2004 to 2005 and not say 2007? It's understandable that people are confused about the lack of results.Potatoswatter 04:57, 19 November 2006 (UTC)


The mission itself ran from 2004 to 2005. It's the data analysis which is still underway

Chrislintott

[edit] Never tested before

This mission is testing some relativistic phenomena that no one has tested before. They might exist or not. If not, General Relativity will be wrong, as someone is already predicting, if so many many people will come to consult this article next April.

[edit] Text referencing arXiv publication

I feel, the new text (quoting a 0.5% accuracy of an MGS analysis) referencing an non-peer reviewed (yet) article on the arXiv server is premature. We cannot use this type of attribution in my reading of WP:RS. The claims related to this should be removed. Awolf002 02:56, 19 January 2007 (UTC)

The text says that a claim has been made, which is true. It's usual in astronomy to cite arXiv preprints pending the (often slow) peer review process. I suggest the text is left unless the paper is withdrawn. Chrislintott 10:26, 19 January 2007 (UTC)

[edit] Aim of the Gravity Probe B experiment

The aim of the Gravity Probe B mission, which the article had stated in the first paragraph until recently as

"to measure the stress-energy tensor (the distribution, and especially the motion, of matter) in and near Earth, and thus to test related models in application of Einstein's general theory of relativity"

was recast, per [1] (Revision as of 09:59, 28 March 2007, "copyedit" by User:Potatoswatter as

"to measure the stress-energy tensor (the distribution, and especially the motion, of matter) in and near Earth, thus testing Einstein's general theory of relativity and our precise models of space."

(The former statement had been in place since Revision as of 19:34, 9 May 2004.)

There's a profound difference between these two statements: The former claims that certain models are being tested, concerning the distribution of stress-energ, or IOW: the distribution and motion of matter, in and near earth (i.e. notions for which definition and method of measurement is provided by the general theory of relativity). The latter claims not only that certain models of space (or: spacetime) are being tested, concerning presumably for instance "curvature" of the region containing earth (i.e. notions for which definition and method of measurement is provided by the general theory of relativity), but it claims also a test of the general theory of relativity itself.

It is straightforward (to me) to point out the view on the aim of the Gravity Probe B mission as "test of certain models (in application of the general theory of relativity)", especially by considering the negative or contrary expectation-sentences

"The model, that the interior bulk mass of earth rotated approx. at the same angular velocity as earth's surface, is wrong if ... (certain finds had been made by the Gravity Probe B mission)", or

"The model, that the region including earth has a particular frame-dragging curvature, is wrong if ... (certain finds had been made by the Gravity Probe B mission)".

(In application of the general theory of relativity, the latter of course represents the definition and method of measurement for the former. Btw.: the experimental determination, that the latter model, and consequently also the former model, are not wrong after all, is IMHO an awesome accomplishment and insight. Had it not been for the Gravity Probe B experiment -- how would we've ever known anything about mass or motion of earths interior?)

On the other hand, I'm unable (at present, by myself) to point out the view, that a test of the general theory of relativity itself were involved; considering in particular the negative or contrary expectation-sentence

"The general theory of relativity itself is wrong if ...".

I'm unable to complete this sentence by referring to particular models, or to certain finds by the the Gravity Probe B mission, which are available (or which are even just about to become available) in application of the general theory of relativity; which in turn cannot be both be applied and presumed wrong in attempting to express a consistent expectation-sentence.

Consequently I'll restore the aim of the Gravity Probe B mission as stated since 2004, incorporating the test of models concerning space (or spacetime curvature) pointed out recently.Frank W ~@) R 07:34, 18 April 2007 (UTC)

[edit] Moving Mission progress to a timeline article?

Would there be consensus to rename the section "Mission progress" to "Gravity Probe B mission timeline" and move it to a separate article? It seems to me that the current section was useful during the data taking campaign, but has now become an "obstacle," when reading this article. Awolf002 11:54, 18 April 2007 (UTC)

I agree. The timeline was quite exciting during the mission (did you, like me, follow the IOC phase day by day, nail-biting stuff!), but the article has to move with the experiment status, which is now practically finished. NeilUK 07:31, 19 April 2007 (UTC)

Okay, I will change that shortly, if nobody else objects. (Yes, it was a nail-biting time when I helped writing that section :) Awolf002 11:16, 19 April 2007 (UTC)

[edit] Added results to the top of the article

Many comments in the discussion ask for results, so I've put them up where they can be seen, without having to wade to the links in the article to the off-site pubs. If you want to edit these a little, that's fine, but please leave at least a mention that the results so far are as expected, right at the top. NeilUK 07:31, 19 April 2007 (UTC) OOps, sorry, didn't intend to create a sock, 193.195.77.146 is me, having an idle wwilf and forgot to log in before editting NeilUK 07:33, 20 April 2007 (UTC)

[edit] There is no known general relativistic prediction of gravitomagnetic effect

There is no known general relativistic prediction of gravitomagnetic effect other than dipole gravity proposed by Jeong. His paper was published in 1999. But no one noticed its implication. Now it seems that the Stanford team needs his theory more than ever because it is the only theory that derives Lense-Thirring force directly from the linearized theory of general relativity. The conventionally known gravitomagentism obtained from the modified Maxwell's equation is not of general relativity. So they should be careful when deciding what theory they have to use to compare the GPB data with. —Preceding unsigned comment added by 70.128.226.243 (talk) 10:59, 31 March 2008 (UTC)