I think this is one of the most delicate experiments ever pulled off by the human race. It requires such precision.

very good mission

Found a link on FARK.

http://science.nasa.gov/headlines/y2...htm?list766847

Says that GP-B is all done gathering data...and now the scientists have to analyze it and figure out what's what.

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"4th Law of Modern Thermodynamics: Where Mihoshi is, Chaos Reigns." ~W. Hakubi
"Gun control is hitting your target; Recycling is reloading your brass." ~ Lex of Dirty Work.

http://einstein.stanford.edu/

That's about a two-month slip from earlier estimates. Reasonable.

Nothing new on the LIGO sites...other than webpage overhauls. The LIGO bodies should be very busy with Science Run 5 (SR5).

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jwj

It's ok not to know. We should try harder to find out.

NASA Gravity Probe B Mission Update 7 July 2006

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Everything I need to know I learned through Googling.

9 Months to go.

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Forming opinions as we speak

Since the effects they are looking for are essentially geocentricin nature, and since the proper derivation thereof was geocentric even though it used relativity, I expect that the numbers will not be fudged too much, if at all, and I expect the effects to be confirmed.

Gravity Probe B's initial science results will be publicly released in a few days' time.

Garth (A. Barber) has compiled a succinct list of all published predictions of what the two key results from GPB will be (they're at the end of this thread).

If you have your own theories, that GPB will be testing, you've only got a few more days to make them public ('prediction' after the fact - a.k.a. 'postdiction' - isn't anywhere near to powerful).

Moved from Astronomy to Space Exploration since we're talking about the results of a space mission (am willing to be persuaded otherwise, though).

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Everything I need to know I learned through Googling.

Let me persuade.......... This is General Relativity and Gravitation, big time. This (assuming GR comes shining through) will be the first direct, local observer on the scene, verification of frame-dragging/gravitomagnetic effects (well, that can be debatable, I guess), along with geodetic precession, a strange effect of spatial curvature.

And note how much stronger the geodetic effect is compared to the gravitomagnetic precession -- 2 orders of magnitude!

Anyway, this will be a seminal notch in the belt of General Relativity.

-Richard

I've tried to come up with a prediction, but after reading about how much work has gone into 'recalibrating after the fact', I fear preconceptions of what the final data should look like can creep into the final numbers.

There is no question additional unanticipated massaging is necessary - the 'perfect' gyroscopes proved to have slightly viscous moments, and the pre-release paper titles indicate they had a harder-than-expected time determining the exact position of calibration stars. (Some of this subtended from using single quasars as absolute standards, a practice suspended in precision astrometrics.)

So the data reduction reported in the Gravity probe B status reports appears to be based upon sound physics. What remains to be seen is whether or not the 'GR signal' can be isolated from other sources of noise, and whether or not these can be legitimately assigned physical causality.

All that said, IAOTO there should be unanticipate effects upon the probe gyros and their spin rates that is best characterized as period functions of the distance of the earth and moon from the sun. Unfortunately, the precision measuring period was less than one year, so this curious result would be less than fully established.

Hopefully, the results will lead to more careful measurements of gravitational potentials within the solar system.

For the few of us that think Titan is covered with silicate sand and gravel, and in general, the Newtonian predictions of masses based upon orbital calculations are severly flawed, the only true test is to start using primary standards in planetary probes; and including instrumentation in outer solar system probes that can absolutely quantify the composition of the moons of the outer planets.

In order for these nonnewtonian predictions to be true, the noise levels - the absolute variance found in the Gravity B probe must be greater-than-expected...and this has already been confirmed to be true. The only question is if they are systemic.

...and I think the reported 'difficulty' in reducing the data has already reduced the expectations of this probe to where 'seminal notch' status is inappropriate. Remember, the PI's insisted that only data reduction routines formalized before the launch would be used to analyse the data. That didn't work.

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jwj

It's ok not to know. We should try harder to find out.

Well, like most such endeavours these days, the team will be releasing all the raw data too* ... so you may perform whatever analyses you wish on it.

I sometimes wonder, Jerry, about comments like these from you ... sweeping, broad, with a hint of some kind of skullduggery ... yet when the relevant teams do^ release all the raw data, it seems you neither mention that fact, nor take the trouble to perform your own analyses on it. Would it be appropriate for you, someday, to start a thread in BAUT's Conspiracy Theories section (so we could require you to defend all your specific, concrete claims)?

*"In addition to providing a first peek at the experimental results at the APS meeting, the GP-B team has released an archive of the raw experimental data. The data will be available through the National Space Sciences Data Center at the NASA Goddard Space Flight Center beginning in June 2007."

^For avoidance of doubt, not every team always releases all the raw data, even after a proprietary period.

Well, if I read it right, geodetic precession has been confirmed to
within 1% of GR's prediction, but the 2 order of mangnitude gravitomagnetic/frame dragging precession is still being worked on, and we'll have to wait until the end of the year when the complete analysis is done to get that.

-Richard

The PR graphic on the geodetic released today looks very good:

http://einstein.stanford.edu/

These are what I am most interested in: Do they provide subtle clues that something might be missing from the equation?

There isn't any doubt in my mind researchers sometimes overstate the confidence levels, or miss-interprete their data because of their prior expectations. Last week's downward revision in the accuracy estimates of the Cosmic Infrared Background power function is a perfect example: http://arxiv.org/PS_cache/arxiv/pdf/...704.1498v1.pdf

This does not mean the first round of estimates were bad science - but the willingness of the same team of researcher to downgrade their original estimates made several years ago is definitely good science!
For this (and most) space-based experiments, we almost have to rely upon the competence of the investigative teams. There is so much merging of engineering and science in this experiment and every parameter is so critical, it is virtually impossible for a third party to approach the raw data in a completely independent way.

Fortunately, there are a lot of reasons to expect fair interpretations from the G-probe B team of researchers-they have been very candid about the performance of their satellite. What I like most, is this quote in the press release from principle investigator:

I could not have stated it better myself.

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jwj

It's ok not to know. We should try harder to find out.

Gravity B probe Executive Summary: (Nice history of the mission & guts and stuff, but no science)

http://einstein.stanford.edu/content...ecSum-scrn.pdf

I find the poster on the gyroscope polhode moment very fascinating:

It is a reasonable explanation, but remember, they studied these gyroscopes for decades and never detected any viscous effects. Why did they suddenly show up in microgravity? To account for this effect, they had to add another term to the standard Euler equation.

Again, everything in this poster appears reasonable, but I still have to ask myself if these gyros should have enough internal viscous movement to cause the dampening, because the Earth-based tests said they do not. Remember, the rotational moments of both Pioneer probes dampened much more quickly than expected, and there is currently no explanation for this dampening. For those of us looking for good alternate theories of gravity, these may be important clues. Now I need to figure out how to compare the 'M shaped" frequencies observed in this orbiting probe with tidal charts for the same period...

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jwj

It's ok not to know. We should try harder to find out.

Jerry,

By saying they added terms to the Euler equation, you're making it sound like they just pulled new physics out of some bodily orifice. What is the Euler equation, it is

I*dw/dt + w x L = T, the torque.

For zero applied torque, that describes the precession, or wobble of a rotating body when w is not parallel to L. When there is no torque, the right hand side is zero. When there is torque, the right hand side is equal to that torque.

What the GP-B team did was simply add a term for the torque. This is a blog by a writer who attended the conference:

http://twistedphysics.typepad.com/co...party_physics/

Everritt said the problem was they modelled the electrostatic "patch effect" on the rotor, but *forgot about the housing* as he put it, according to the above author.

There was nothing there but an *unexpected* classical torque on the gyros that they had not anticipated. And if you'll read all the information on this incredible, unbelievable precise gyro, control, and measurement system, you'll see there were a lot of other torques on the gyros they were aware of and were ready for. Considering this was the first launch and operational test of this system, one can only marvel at how well they did model and anticipate all the effects they would encounter. Because this additional effect that had not anticipated, it could look like the signal they were looking for, which is why they were so meticulous about checking it out.

And all of these effects are so incredibly small relative to what we think is significant that it blows you away. The change in rotational energy due to the patch-drag was 10^-13W.

-Richard

Yes, the addition of the term in the Euler equation is reasonable, and so are the explainations. But they are applying new calibration factors that were not anticipated, and are based upon deviations from the expected results.

The team argues this is possibly the most technically difficult experiment ever conducted, and I agree.

That's two unexpected parameters, both of which have been precisely modeled, and they are still crunching on the data, and do not expect to complete the analysis for another nine months. The question is, how many more post-facto parametric adustments will be necessary? If in the final analysis, they were to say 'Einstein was wrong'; the general community would look at the parametric breeding and say 'the experiment lacked proper controls'.

For those of us predicting the results should contain unexpected parametric swings, the question has to be ask: Are the explanations for the unexpectations arrived upon by the team the only reasonable answers?

Another way to state this, is if it is ALWAYS assumed only known physics are in play, how could we ever recognize true deviations? Once again, let me be the Devil's advocate:

The periodic and random changes in the probe housing relative to the test mass are a direct response to the local atmosphere, gravity fields, lunar orbits and so on. The gyroscopes are supposed to be isolated from these reorientations, only deviating when 'space itself' is altered. But what if the response of the gyros is a direct, unexpected effect upon both the gyro and the housing, not coupled to the gyros from the housing by electrostatic patches? These are the uncontrolled conditions that crop up when a unexpected, uncalibrated, correction is required. The more unexpected parameters that are needed, the higher the probability that the initial assumptions are flawed.

When the Mars Phoenix probe falls faster-than-expected next year, for the tenth straight time, will it be blamed upon three sigma variations in the atmosphere?

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jwj

It's ok not to know. We should try harder to find out.

But Jerry, with very few exceptions, we all do processing of all astronomical (and 'physics in the lab') work, all the time!

Take any modern instrument: it's built according to certain theories, tested according to those theories, and used to make observations (experiments) within the framework of those theories.

How could it be otherwise?

And as for testing results such as those from GPB, within the framework of some new idea, well, sometime later this year the team will release all the raw data ... so you can do whatever analyses you wish on it (just as, IIRC, the COBE and WMAP teams also released all the raw data too).

Surely the best way to demonstrate an alternative is to actually work one out, in quantitative form? Then publish it, and show, from analysis of the raw data, that it is consistent?