Can someone tell me if GP-B has results about GR, one way or the other?

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Discussion Overview

The discussion revolves around the results of the Gravity Probe B (GP-B) experiment and its implications for General Relativity (GR), specifically regarding the geodetic effect and frame dragging. Participants explore the status of the results, the impact of unexpected experimental errors, and the anticipated future findings.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about whether GP-B has produced results consistent or inconsistent with GR effects, citing unexpected errors that may have obscured the findings.
  • Another participant notes that the first results published in April 2007 confirmed the geodesic precession prediction to within 1.5%, but the frame-dragging results were overwhelmed by noise.
  • There is mention of a diagram from a December mission update that suggested results inconsistent with GR at the 1 sigma confidence level, though this claim was later retracted.
  • Some participants speculate that the unexpected errors might prevent GP-B from detecting frame dragging, with one expressing growing skepticism about the ability to extract meaningful results from the data.
  • Another participant highlights the challenges of measuring small effects and notes the lengthy analysis process due to previously unmodeled effects that need to be accounted for.
  • Confidence was expressed at an April APS conference regarding the ability to remove noise and achieve accuracy in measuring precessions, although this represents a significant loss in expected precision compared to initial design goals.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the results of GP-B, with multiple competing views regarding the impact of experimental errors and the potential for future findings to confirm or falsify GR predictions.

Contextual Notes

Participants note limitations related to unexpected experimental errors and the challenges of measuring small effects, which may affect the interpretation of GP-B's results.

rbj
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I just can't figger it out from their website. Does GP-B have results that are either consistent with or not consistent with the geodetic effect or frame dragging or gravitomagnetism? Or is it that the unexpected errors swamped the difference in gyro alignment that would have been apparent if these GR effects were happening to the gyros.

It's been months since April 2007 and years since they collected the data. Has GP-B produced results that confirm or falsify the predicted effects of GR? Or not? Or not yet?
 
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You find this discussed here at length.

Basically there were two unexpected experimental errors that swamped the results. The team have been modelling these errors using two different methods, geometrical and algebraical, in order to be able to subtract them from the data. Having two different methods means they can cross check the results.

The first results published in April 2007 confirmed the GR geodesic precession prediction to within 1\frac{1}{2}%, which was consistent with GR given the remaining error bars on the results. The much smaller frame-dragging result was then still swamped by noise.

The full results are now expected in May 2008 (I think they must be paid by the day :biggrin:).

Very interestingly in the Dec Mission Update there was a very intriguing diagram uploaded that showed the recent detailed results of 85 days worth of data and gave a result that was inconsistent with GR at the 1 \sigma confidence level (68%).

Einstein expectation: -6571 \pm 1 mas
4-gyro result (1 sigma) for 85 days
(12 Dec 04 -- 4 Mar 05) -6632 \pm 43 mas

This has now been replaced by a similar http://einstein.stanford.edu/cgi-bin/highlights/showpic.cgi?name=GR-85-day_result.jpg which makes no such claim!

Are they hiding something? :wink:

We wait for the most accurate results next May with some anticipation!

Garth
 
Last edited by a moderator:
See also [post=1303301]this old PF post[/post] by myself.
 
Chris Hillman said:
See also [post=1303301]this old PF post[/post] by myself.

i saw that back then, Chris. i was hoping for news of developments since. it seems to me that because of the unexpected errors, that GP-B might have failed to detect either the presense or absense of frame dragging. maybe they'll be able to rescue the subtle differences out of additive errors that are much bigger, but I'm starting to be less hopeful.
 
Everyone must wait and see. Science is tricky and these experiments are looking for very small effects, so given the previously unmodeled effects which must be subtracted, it is perhaps not so surprising that analysis is taking so long.
 
At the April APS conference they were confident that they will be able to remove the unexpected noise in the data and obtain both precessions to an accuracy of \pm1mas.

Initially they had designed the experiment to an accuracy of \pm0.1mas, so they have lost an OOM.

Nevertheless that will confirm, or otherwise, the GR frame dragging prediction to within \pm2% and the geodetic precession to within \pm0.02%.

Garth
 

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