Alternative theories being tested by Gravity probe B

[LeBourdais]

The spin axes of all four gyros were aligned with IM Pegasi. These are its coordinates, posted previously by Garth:

RA (J1991.25) : 22h 53m 02.279"
DEC (J1991.25) : +160 50' 28.540"

Hi Kris,

Do you mean to say that the spin of the four gyroscopes have been initially aligned in the same direction ?

That sounds strange

Paul

 

[Kris Krogh]

Hi Paul,

It's a good system. Without this redundancy, they would be in a bad situation now. They need be able to compare the outputs of multiple devices to correct errors. Two rotate one way, and two the other, but they all have the same axis of rotation. You can find this kind of information on the GP-B web site.

Kris

 

[cosmopot]

New clothe put on the king

I wrote lots of papers and chatted on many forums but no one challenge my points:
1. GR is nothing but curved spacetime;
2. On curved spacetime, coordinates are not the accurate values of spatial distance or temporal interval or spatial angle.
3. To have those accurate values we need to perform integration with metric form being integrand. However, I did not see anyone do so to achieve distance, or angle, or time interval on curved spacetime. Instead, people simply write r, t, \phi and assume they are distance, time, angle respectively.

I am driven crazy by this fact with which many great figures (Einstein, Hilbert, John Baez, Steve Carlip, Francis Everitt being associated.

You can not say spacetime is curved because you have the terminology with some quantities: metric, cutvature, covariance. For example, quantum mechanics uses distance, radius which do not mean we can have definite orbits of micro-particles!

Is there anyone answering my question??

You know flat space is nothing but:
ds^2=dx^2+dy^2

flat Minkowski spacetime is nothing but:
ds^2=-c^2dt^2+dx^2+dy^2+dz^2
where
ds=dx if dt=dy=dz=0
and
dT=cdt =c time if dx=dy=dz=0 where dT^2=-ds^2

curved spacetime is nothing but:
ds^2=-Ac^2dt^2+Bdx^2+Cdy^2+Ddz^2
where
ds=sqrt(B)dx if dt=dy=dz=0
and
dT=sqrt(A)dt = c time if dx=dy=dz=0 where dT^2=-ds^2
Therefore, t is not time because A varies with position on curved spacetime manifold.

 

[LeBourdais]

It's a good system. Without this redundancy, they would be in a bad situation now. They need be able to compare the outputs of multiple devices to correct errors. Two rotate one way, and two the other, but they all have the same axis of rotation. You can find this kind of information on the GP-B web site.

Thanks a lot Kris ! That's really interesting. I will check on the GP-B web site.

By the way, I have received the answer to my question from GP-B Web Site Curator: for the moment now, they got no "best value" for the frame-dragging effect.

Paul

 

[Kris Krogh]

Hi Paul,

I emailed the same address in 1999, to ask when they expected to launch the probe. It was scheduled for that October, but everyone knew they were running way behind. The response was that they were on schedule, and maybe would move the launch ahead to July. (Nice creative touch.) They ended up launching in 2004.

If you believe they have no idea how this measurement compares to the expected frame dragging, you're as gullible as I've been about their scheduling of the launch, release of data and analysis. (These delays have hurt me badly.) You can't blame the GP-B people entirely, because politics and diplomacy are necessary to carry out a project like this.

Kris

 

[LeBourdais]

Hi Kris,

Of course they probably know more than they say, but something sure, they won't give a "best value" for frame-dragging before they are ready to do so. Until they do, we can only speculate.

Paul

 

[henryco]

Hi Kris,

Of course they probably know more than they say, but something sure, they won't give a "best value" for frame-dragging before they are ready to do so. Until they do, we can only speculate.

Paul

If it is in conflict with GR, they will never dare give the central value for the frame dragging...which is dramatic since, if all experimentalists behave this way as soon as they get an anomaly...progress is hopeless!
However they can at least answer my simple questions to let us make up our proper mind, and take our own responsability of what we have to say about the result:
How did they obtain the East-West plot?, what was subtracted before?
What does the graph look like for other Gyros?

i didnt got any answer, but i was trying to reach Everitt himself. May be i should better try the email of the guy that has answered your question.
What is it?

cheers,

F H-C

 

[LeBourdais]

If it is in conflict with GR, they will never dare give the central value for the frame dragging...which is dramatic since, if all experimentalists behave this way as soon as they get an anomaly...progress is hopeless!

Salut Fred,

Do you mean to say that they would have spent 800 millions dollars to send GP-B in space with the intent of not giving the results if these were contradictory with GR ?

i didnt got any answer, but i was trying to reach Everitt himself. May be i should better try the email of the guy that has answered your question.
What is it?

There is no secret about it, it's the e-mail address provided on GP-B Web site: www@relgyro.stanford.edu
The person that answered to me is the Web Site Curator.

Take it easy Fred

Friendly,

Paul

 

[jgraber]

Preliminary Frame Dragging "Glimpse"

I am posting from the APS meeting in Jacksonville.
You can see the preliminary result that was presented here,
with lots and lots of caveats,
by going to the GPb Homepage,
http://einstein.stanford.edu/index.html
and clicking on poster L1.00028,
Gravity Probe B Science Data Analysis: Filtering Strategy.
The result is called
"Glimpses of Frame Dragging"
and is in the bottom right quadrant of the poster.
One "glimpse" differs from GR by about two sigma,
but everything is still preliminary,
including the size of the sigma,
which is of order 10 mas/y
i.e. milliarcseconds per year.
I believe this particular "glimpse" is based on about 40 days data from one of the gyros.
Also, they have not yet unblinded themselves from the improved drift of the guidestar.
However, they still hope/expect to reduce their sigma to 1 or 2 mas/y by December.
Francis said there may be a small hint of a difference with GR,
but it is still much too early to talk about this seriously.
Jim Graber

 

[henryco]

I am posting from the APS meeting in Jacksonville.
You can see the preliminary result that was presented here,
with lots and lots of caveats,
by going to the GPb Homepage,
http://einstein.stanford.edu/index.html
and clicking on poster L1.00028,
Gravity Probe B Science Data Analysis: Filtering Strategy.
The result is called
"Glimpses of Frame Dragging"
and is in the bottom right quadrant of the poster.
One "glimpse" differs from GR by about two sigma,
but everything is still preliminary,
including the size of the sigma,
which is of order 10 mas/y
i.e. milliarcseconds per year.
I believe this particular "glimpse" is based on about 40 days data from one of the gyros.
Also, they have not yet unblinded themselves from the improved drift of the guidestar.
However, they still hope/expect to reduce their sigma to 1 or 2 mas/y by December.
Francis said there may be a small hint of a difference with GR,
but it is still much too early to talk about this seriously.
Jim Graber

Thank you very much for these informations...the problem is that i was not able to understand these plots mainly because of the bad resolution in the scanned axis...i still don't see what the axis in the ellipses plots represent:
the y-axis seems to be frame dragging , but the x-axis not sure: a north/south effect?
Does the expression "glimpses so far" mean that for the time being it was not possible to extract a continuous frame dragging behind those glimpses?
Are those glimpses the same resonance peeks shown in the east-west plot of the GP-B error poster?
Since you are in Jacksonville may be you have this information.

Thank you again



F H-C

 

[henryco]

Salut Fred,

Do you mean to say that they would have spent 800 millions dollars to send GP-B in space with the intent of not giving the results if these were contradictory with GR ?

Salut Paul,

Of course not... and i apologize. But it's too frustrating for me not
to attend the APS conference and i have difficulties to correctly interpret
the information given on the posters...

Take it easy Fred

Friendly,

Paul

You are right Paul

amiclt,

Fred

 

[makc]

people simply write r, t, \phi and assume they are distance, time, angle respectively

but no one assumes that they are same distance, time, angle as in flat Minkowski spacetime, or do they?

 

[jgraber]

henryco,
the other axis is the geodetic effect.
The center of the largest ellipse is close to the expected GR value.
Jim Graber

 

[henryco]

henryco,
the other axis is the geodetic effect.
The center of the largest ellipse is close to the expected GR value.
Jim Graber

OK but as far as i know frame dragging must be continuous, not only happen from time to time as isolated glimpses (or did i miss something? somebody can confirm or invalidate this?)...otherwise this has nothing to do with GR frame dragging. What on Earth does this glimpse mean? Once we admit that this measurement is very preliminary and that no one should draw conclusion about it, there should be no problem for the experimentalist to answer this simple question: what does glimpse mean here? does it mean that from time to time there appears to be a short time burst of frame dragging (june 2006...) and that nothing is detected in between two such manifestations so far?
or is this glimpse simply due to the observer selection of a short period of time?
The first is the interpretation i must take the more serious since otherwise i would not be able to understand the question "why glimpses so far?". Moreover i understand in this case why their dominant error comes from the resonance peeks shown in the back/left plot in the error poster since such peeks can really mimic a momentaneous burst of frame dragging but obviously not a constant drift rate. If you are still in Jacksonville may be can you ask some member of the GP-B team these questions...my emails are never answered! what on Earth is going on? am i a plague-stricken?

Best regards and thank you for your help if you can get this information/confirmation.

F H-C

 

[jgraber]

The fractional data is due to two things: 1 They are not yet done analyzing it.
2. The spacecraft shut down briefly nine times during the eleven months of science data taking.
they are working on "stitching it together."
Best.
Jim Graber

 

[Kris Krogh]

Francis said there may be a small hint of a difference with GR,
but it is still much too early to talk about this seriously.
Jim Graber

Hi Jim,

Thanks very much for the information! Does the possible small hint Francis mentioned refer to frame dragging specifically? Also, do you have any sense whether this is in the direction of a larger effect, or smaller than expected?

As F H-C mentioned, on the two charts of the modeled Gyro 3 torque, we can't read any of the labels or numbers on the axes, or the other fine print. Can you fill us in? Also, do the ellipses indicate bounds on possible values?

Best wishes,

Kris Krogh

 

[LeBourdais]

As F H-C mentioned, on the two charts of the modeled Gyro 3 torque, we can't read any of the labels or numbers on the axes, or the other fine print.

Hi Kris,

If we look at the upper chart ("Torque Modeling Example : Motion of Gyroscope 3"), the dashed line is referred to as the "estimated relativistic motion" and it is clearly not flat. Therefore, whatever the numbers on the axes, I guess we can conclude that their "best value" for frame-dragging is not zero. Am I missing something ?

Paul

 

[magnetar]

Gravity probe-b backs general relativity!

http://physicsweb.org/articles/news/11/4/11/1

 

[henryco]

Hi Kris,

If we look at the upper chart ("Torque Modeling Example : Motion of Gyroscope 3"), the dashed line is referred to as the "estimated relativistic motion" and it is clearly not flat. Therefore, whatever the numbers on the axes, I guess we can conclude that their "best value" for frame-dragging is not zero. Am I missing something ?

Paul

hi paul

I would say:
1) it depends if the y-axis actually shows a pure east-west deviation, doest it (i can't decode the y-scale)?
2) even an actual east-west effect can have another origin than frame dragging (for example if we are in the vicinity of resonance peeks as shown in the error poster)...
3) The latter remark is reinforced if the (even preliminary) fitted drift rate is at several sigmas from GR prediction! If i now decode well the scales on the "glimpses plot" there are four glimpses at respectivily and approximately 2,3,8,8 standard deviations from the GR prediction !

Cheers,

Fred

 

[Kris Krogh]

Hi Paul,

You have a point there, at least as far as this particular graph is concerned. I contacted the web page curator, and I think she'll put up a more readable version of this poster for us tomorrow.Magnetar,

That article says the geodetic effect of general relativity has been measured. But that's already been measured more accurately in other ways. The important one for me is frame dragging. They say Gravity Probe B hasn't measured that yet.

 

[jgraber]

Hi everyone,
Sorry I can only post on coffee breaks when I am near the APS temporary hotspot. As I understand the "glimpses" each ellipse is a one sigma radius, and GR is very near the center of the earliest, crudest glimpse, and about two radii (i.e. approx two sigma) from the smallest, latest "glimpse", which is still based on a very limited amount of not yet fully processed data. As I understand it, the data in that plot are total motions, including nonrelativistic effects as well as the two GR effects. The speakers mentione three or four of order 40-80 mas/y total that add to the Geodetic Effect and at least one of order 40mas/y that adds to the Frame Dragging Effect. Because of these additions, the GR prediction is offset from the values usually quoted. The values on the "glimpse" chart have minus signs and increase in absolute value downward and to the left. They increase (or decrease) by 20 per grid line and the central values are 80 for the vertical (Frame Dragging) axis and 6580 for the horizontal (Geodetic) axis. The latest "Glimpse" is slightly offset in the direction of larger values, so IF you take it at face value, which is wildly over optimistic in my opinion, it would indicate that both effects are slightly larger than the GR prediction by about 10 mas/y compared to 6600 and 40. However, there will be new, much more reliable numbers in December or so, and the only sensible course in my opinion is to wait until then. remember, there are systematic as well as statistical errors, and the experiment is quoting their current overall sigma as 90-100 mas/y. This is small compared to the Geodetic effect, but totally swamps the Frame Dragging effect. They say the Geodetic effect is totally obvious from the rawish data, but the Frame Dragging Effect must be dug out of the noise. Remember, they found two major unexpected noise sources, and for several months were afraid that they would not be able to report any frame dragging result. It is only because of the large amount of redundancy in the data and the fact that the two GR effects and the two unexpected noise sources have four different mathematical characteristics that they expect to be able to recover something close to the originally expected accuracy.
Jim

 

[LeBourdais]

Thank you very much Jim ! It gives me a better picture of what's going on.

Paul

 

[Kris Krogh]

Jim,

Thanks very much for your insights! That all seems to add up. Would it be possible to confirm with someone there from GP-B that the best of this data would hint at a slightly larger than expected frame-dragging effect? (If it hints at anything.)

Best wishes,

Kris

 

[Garth]

I have just returned from the APS Meeting at Jacksonville and a holiday in Florida.

As has been well discussed the first results have verified the GR geodetic prediction to 1% but there is no handle on the frame-dragging prediction, basically because unexpected signals so far swamp it, except for 'glimpses'.

By the end of the year the correct removal of these effects will give a robust reading to both precessions.

The running now stands:

1. Einstein's General Relativity(GR)
2. Brans-Dicke theory (BD)
3. Barber's Self Creation Cosmology (SCC),
4. Moffat's Nonsymmetric Gravitational Theory (NGT),
5. Hai-Long Zhao's Mass Variance SR Theory (MVSR),
6. Stanley Robertson's Newtonian Gravity Theory (NG),
7. Junhao & Xiang's Flat Space-Time Theory (FST).
8. R. L. Collin's Mass-Metric Relativity (MMR) and
9. F. Henry-Couannier's Dark Gravity Theory (DG).
10. Alexander and Yunes' prediction for the Chern-Simons gravity theory (CS).
11. Kris Krogh's Wave Gravity Theory (WG)
12. Hongya Liu & J. M. Overduin prediction of the http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v538n1/50681/50681.text.html?erFrom=5252751197746712308Guest#sc8 gravity theory (KK).
13. Kerr's Planck Scale Gravity: now accepted for publication Predictions of Experimental Results from a Gravity Theory (PSG)

The following are still in the running:

GPB Geodetic precession (North-South)
1. GR = 6.6144 arcsec/yr.
2. BD = (3\omega + 4)/(3\omega + 6) 6.6144 arcsec/yr. where now \omega >60.
4. NGT = 6.6144 - a small \sigma correction arcsec/yr.
6. NG = 6.6144 arcsec/yr.
9. DG = 6.6144 arcsec/yr.
10. CS = 6.6144 arcsec/yr.
11. WG = 6.6144 arcsec/yr.
12. KK = (1 + b/6 - 3b² + ...) 6.6144 arcsec/yr. where 0 < b < 0.07.

We await the GPB gravitomagnetic frame dragging precession (East-West) result.

1. GR = 0.0409 arcsec/yr.
2. BD = (2\omega + 3)/(2\omega + 4) 0.0409 arcsec/yr.
4. NGT = 0.0409 arcsec/yr.
6. NG = 0.0102 arcsec/yr.
9. DG = 0.0000 arcsec/yr.
10. CS = 0.0409 arcsec/yr. + CS correction
11. WG = 0.0000 arcsec/yr.
12. KK = 0.0409 arcsec/yr.Those that have fallen by the wayside:

3. SCC = 4.4096 arcsec/yr.
5. MVSR = 0.0 arcsec/yr.
7. FST = 4.4096 arcsec/yr.
8. MMR = -6.56124 arcsec/yr.
13. PSG = 0.0000 arcsec/yr.

Garth

 

[LeBourdais]

As has been well discussed the first results have verified the GR geodetic prediction to 1% but there is no handle on the frame-dragging prediction, basically because unexpected signals so far swamp it, except for 'glimpses'.

By the end of the year the correct removal of these effects will give a robust reading to both precessions.

Hi Garth,

Thank you for this status.

Sorry for your theory.

Best wishes
Paul

 

[Garth]

Hi Garth,

Thank you for this status.

Sorry for your theory.

Best wishes
Paul

Thank you for your commiserations!

Garth

 

[magnetar]

I do not understand why so many "Alternative theories" about gravity?
why so many controversial ??

 

[sylas]

I have just returned from the APS Meeting at Jacksonville and a holiday in Florida.

Hi Garth,

Can you explain the difference between the 6614.4 and 40.9 being quoted in numerous sources before the APS meeting(including many still available in the GP-B site) and the 6606 and 39 numbers now being used? (numbers being GR expectations for geodetic and framedragging effects in milliarcsec/yr)

I'm guessing it could be a difference in the altitude of the final orbit, but I don't know.

Cheers -- Sylas

 

[Garth]

That is a good question that wasn't addressed at the meeting, I have only recently become aware of that anomaly myself.

The posters clearly show the latter (6606 and 39 mas/yr) set of values while all their previous literature showed the former (6614.4 and 40.9 mas/yr) set.

The orbit decreased in SMA by about 350 metres during the lifetime of the experiment, but that should have increased the expected precessions by about one part in 10^-4 in my estimation.

The present measured value of the geodetic precession is 6638 +/- 97 mas/yr. (Francis Everitt APS Plenary Session 14th April 07)

Note however on the Gravity Probe B Science Data Analysis: Filtering Strategy poster (Click on the title), it says of the geodetic measurement:

Current Estimates (“Glimpses”)
-6595 ± 10 milliarcsec/year
-6604 ± 7 milliarcsec/year

GP-B website:

The experiment’s final result is expected on completion of the data analysis in December of this year. Asked for his final comment, Francis Everitt said: "Always be suspicious of the news you want to hear."

Garth

 

[sylas]

That is a good question that wasn't addressed at the meeting, I have only recently become aware of that anomaly myself.

OK... I have gone back to first principles, and I think I have sorted this one out.

The information at the GP-B seems pretty sloppy. I have checked out the Fact Sheet, dated February 2005. The information therein is inconsistent.

Here are the orbit characteristics...

Orbit

Characteristics Polar orbit at 642 kilometers (400 miles), passing over one of the poles every 48.75 min.
Semi-major axis 7,027.4 km (4,366.6 miles)
Eccentricity 0.0014
Apogee altitude 659.1 km (409.5 miles)
Perigee altitude 639.5 km (397.4 miles)

The semi-latus rectum (wiki ref) is given as:
a*(1-e^2) = 7.0274*10^6*(1-0.0014^2) = 7.027386226*10^6
which is the same a, up to five figure accuracy.

The formula for geodetic precession is 1.5(GM)^{1.5}c^{-2}R^{-2.5}, where R is the semi-latus rectum (ref: Gravitation and cosmology, S. Weinberg (1972) [pp237-8]).

Plug in
<br /> G = 6.6742*10^{-11},<br /> M = 5.976*10^24,<br /> c = 299792458<br />

and we get 1.0155*10^{-12} rad/sec, or 6.60559 arcsec/yr.

However, the same press release, with these same orbit parameters, gives 6.6144

I'm guessing they had already calculated 6.6144 from a projected orbit; and then recalculated for the actual orbit, but did not properly update all the recorded predictions.

The value 6.6144 implies an orbit about 3.7 km smaller in radius.

Now… what formulae do I need to use for the Lense-Thirring effect?

Cheers -- Sylas