Heard anything about GPB results?

[marcus]

Today on some astronomy blog I read about the ongoing analysis of GPB data, but I no longer have the link. Does anyone have anything current?

Here, for starters, are some old press releases

http://www.spaceref.com/news/viewsr.html?pid=19819
(as of 28 February 2006)
"...We are now entering Phase II of the data analysis, which will last 4-5 months. During this phase, the team will ..."

http://www.spaceref.com/news/viewsr.html?pid=21294
(as of 7 July 2006)
"...As of July 7, we are continuing to progress through Phase II of the data analysis process, which began at the beginning of March and is scheduled to run through late August 2006. During Phase II, our focus is on understanding and compensating for certain long-term systematic effects in the data that span weeks or months. The primary products of this phase will be monthly spin axis precession estimates for each gyro, as well as refined daily spin axis orientation estimates. In this phase, the focus remains on individual, rather than correlated gyro performance. ..."

What I've heard leads me to expect no surprises, but I could be wrong---may have misunderstood something. Anybody else have views they want to express at this stage?

 

[Garth]

The best site from the 'horse's mouth' is Gravity Probe B.

Nobody will know the results until January 2007.

In Phase III, which is scheduled to run from late August 2006 through December 2006, data from all four gyros will be integrated over the entire experiment. The results of this phase will be both individual and correlated changes in gyro spin axis orientation covering the entire 50-week experimental period for all four gyros. These results will be relative to the position of our guide star, IM Pegasi, which changed continually throughout the experiment. Thus, the final step in the analysis, currently scheduled to occur in January 2007, will be to combine our gyro spin axis orientation results with data mapping the proper motion of IM Pegasi relative to the unchanging position of a distant quasar. The proper motion of IM Pegasi has been mapped with unprecedented precision using a technique called Very Long Baseline Interferometry (VLBI) by Irwin Shapiro and his team at the Harvard-Smithsonian Center for Astrophysics (CfA), in collaboration with Norbert Bartel at York University in Toronto and French astronomer Jean-Francois Lestrade.

The results will be published in April 2007.

Garth

 

[Chronos]

I think GPB will confirm what has already been deduced from binary neutron star systems, but, its still an important test of GR.

 

[wolram]

I think GPB will confirm what has already been deduced from binary neutron star systems, but, its still an important test of GR.

And what will you do if the results do not confirm modern theory? I guiess most will find a way to denounce it, who will abide from this one test?

 

[MeJennifer]

And what will you do if the results do not confirm modern theory? I guiess most will find a way to denounce it, who will abide from this one test?

I suspect that the die-hard GR believers would simply postulate, with a straight face, some invisible force or mass. Then they would univocally prove with a thought experiment that this new force or mass exactly compensates for the measurement.

 

[SpaceTiger]

What are you two going on about? The whole point of launching missions to test GR is to do just that, test GR. If people just ignored the results, it would kind of defeat the purpose, don't you think? Whenever a new result contradicts established theory, it is always greeted with skepticism, since experiments are often wrong and there are countless reasons why the result could be erroneous. However, it is generally not ignored.

If GPB reports a discrepancy with GR, the obvious thing to do is to look for other theories that might have predicted the discrepancy (if any). Then look to see what other predictions the theory or theories make that can be tested in the short-term. If any of those predictions are tested and also confirmed, then we will likely have a new mainstream theory of gravity.

 

[Garth]

We wait and see!

Garth

 

[marcus]

Francis Everitt spoke yesterday at the MG11 conference in Berlin.

He has been the principal investigator of GPB ever since 1981

(before that, from 1966-1981 he was co-principal investigator). I guess next to Leonard Schiff, who dreamed up GPB, but died young, you could say that GPB is Francis Everitt's baby and has been from the get go.

The Marcel Grossmann conference happens every 3 years and is THE main international GR conference. This year MG11 was the eleventh in the series.
Most of the Plenary Session talks (the ones by prominent people that everybody attends, as opposed to parallel session talks in various subspecialties) are available in ONLINE streaming VIDEO.

However the talk by Francis Everitt on GPB is NOT AVAILABLE ONLINE.

My experience with the WMAP3 data was that there were people who knew general kinds of stuff earlier BEFORE the official release of the results. My guess is that Everitt is one of those who has or will have an earlier feel for how the results are turning out----earlier than the official release of the results. So his talk to the gravity specialists at MG11 might (or might not) have contained some hints.

Here is a link about Everitt:
http://einstein.stanford.edu/cgi-bin/people_test/data/show_person.pl?C._W._Francis=Everitt
here is a link about MG11 conference in Berlin
http://www.icra.it/MG/mg11/

If they ever get around to putting video of Everitt's talk online, it is the Saturday 29 July timeslot of 9:30-10AM.
they have the video's listed by day and time. It was a 6 day conference. that is how you would find it because the videos are not listed by speaker.

BTW in case anyone is interested in Quantum Gravity, the Plenary Session talk on QG was given by Abhay Ashtekar on the second day of the conference----25 July in the 11-13 timeslot (11AM-1PM)---starting about halfway through. You have to fast forward if you want to skip the first speaker.

Also BTW personally I think that between them, MOND and non-string QG may possibly come up with significant corrections of Gen Rel and make testable predictions (in fact both have already made testable predictions). So eventually some gravity experiment could find that GR predicts WRONG and some prediction arising out of MOND and/or QG could turn out right. Of course that is just my guess but I sense something like that is in the works, and that would be according to the way science has happened in the past. These highly successful theories nevertheless always have some flaws or limitiations and eventually something more fundamental theory (from which the old one arises as a useful approximation) makes an appearance.

 

[marcus]

The whole point of launching missions to test GR is to do just that, test GR. If people just ignored the results, it would kind of defeat the purpose, don't you think? ...
...
... If any of those predictions are tested and also confirmed, then we will likely have a new mainstream theory of gravity.

absolutely agree. In a sense the best thing we could hope for is some discrepancy that would surprise everybody and stimulate them modify the theory of gravity.
the prospect of still another umpteen digit precise verification of the classical theory is not too inspiring. Or maybe it is, but right now it strikes me as blah.

 

[Garth]

Thank you Marcus for that link.

Francis Everitt's abstract of his talk:

The Gravity Probe B relativity gyroscope mission was launched from Vandenberg Air Force Base on 20 April, 2004. GP-B tests: 1) the 6.6 arc-s/year geodetic effect due to the motion of the gyroscope through the curved space-time around the Earth; 2) the 0.041 arc-s/year ‘frame-dragging’ effect due to the rotating Earth. The mission has required the development of cryogenic gyroscopes with drift-rates 7 orders of magnitude better than the best inertial navigation gyroscopes. These and other essential technologies, for an instrument which once launched must work perfectly, have come into being as the result of an intensive collaboration between Stanford physicists and engineers, NASA and industry. GP-B entered its science phase on August 27, 2004 and completed data collection on September 29, 2005. Publication of the science results is planned for April 2007. In addition to describing the science and technologies, an account will be given of the real-life experience of setting up and operating a physics experiment in space.

I don't think he gave anything away - just yet!

Garth

 

[rusty]

The gpb test of GR.

What are you two going on about? The whole point of launching missions to test GR is to do just that, test GR. If people just ignored the results, it would kind of defeat the purpose, don't you think? Whenever a new result contradicts established theory, it is always greeted with skepticism, since experiments are often wrong and there are countless reasons why the result could be erroneous. However, it is generally not ignored.

If GPB reports a discrepancy with GR, the obvious thing to do is to look for other theories that might have predicted the discrepancy (if any). Then look to see what other predictions the theory or theories make that can be tested in the short-term. If any of those predictions are tested and also confirmed, then we will likely have a new mainstream theory of gravity.

I am very happy that the gpb test is going well, and that the results will be known soon. My 2000 theory of mass-metric gravity (arXiv 0012059) gives the same answers as GR for the 3 classical tests, but predicts the absence of any out-of-plane Lense-Thirring precession for the gpb which is predicted by GR to be .042 arcsec/yr in the direction of Earth's rotation. I feel there will be a smaller out-of-plane precession, -0.1924 arcsec/yr, in the opposite direction and caused by the geodetic precession of the yearly rotation of Earth about the sun. Time will tell.

 

[sylas]

I am very happy that the gpb test is going well, and that the results will be known soon. My 2000 theory of mass-metric gravity (arXiv 0012059) gives the same answers as GR for the 3 classical tests, but predicts the absence of any out-of-plane Lense-Thirring precession for the gpb which is predicted by GR to be .042 arcsec/yr in the direction of Earth's rotation. I feel there will be a smaller out-of-plane precession, -0.1924 arcsec/yr, in the opposite direction and caused by the geodetic precession of the yearly rotation of Earth about the sun. Time will tell.

Rusty, I am trying to check out predictions of Gravity Probe B. Can you please clarify your predictions on the geodetic effect? In a previous post msg #25 of "Alternative theories being tested by Gravity probe B" you seem to propose a shift of -6.56124 arcsec/year in the reverse direction as expected by GR.

Thanks -- Sylas