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View Full Version : Gravity Probe B - 95 years later General Theory of Relativity still making correct predictions.



Munnkeyman
06-05-2011, 08:25 PM
One of the most controversial experimental satellite programs, due to cost versus benefits realised, has finished and the findings have been published after five years of data analysis.
Geodetic precession(de Sitter effect) was measured at 6,601.8 +/-18.3 milliarcseconds per year and Frame-dragging precession(Lense-Thirring effect) was measured at 37.2 +/-7.2 milliarcseconds per year.


http://einstein.stanford.edu/highlights/GP-B-Expt-with-SV_0407large.jpg
Image: NASA

Here's the conference with the following speakers.
Bill Danchi, Francis Everitt, Rex Geveden, Colleen Hartman and Clifford M. Will.
YouTube - Einstein Passes Tests by NASA's Gravity Probe B



Geodetic precession, in simple terms, is the effect realised by an orbiting body due to the curvature of spactime caused by the central mass.
Frame-dragging precession is a broadly similar effect but is due to the rotation of a central mass.

http://large.stanford.edu/courses/2007/ph210/bechtol2/images/fig1big.gif
http://www.politicalworld.org/Geodetic%20precession,%20in%20simple%20terms,%20is %20the%20effect%20realised%20by%20an%20orbiting%20 body%20due%20to%20the%20curvature%20of%20spactime% 20caused%20by%20the%20central%20mass.%20Frame-dragging%20precession%20is%20a%20broadly%20similar %20effect%20but%20is%20due%20to%20the%20rotation%2 0of%20a%20central%20mass.

C. Flower
07-05-2011, 12:27 AM
So, did time get squashed ?

Count Bobulescu
07-05-2011, 08:49 AM
Munnkeyman,

Given that you are a science guy, (I’m interested, but mostly don’t understand) thought you might be interested in the following links.

NPR has a daily two hour current affairs program called Talk of the Nation. On Fridays it is called Talk of the Nation – Science Friday. For me, it airs 2pm eastern, 7 pm Irish. It’s also available via itunes and RSS.

One of the segments May 6, was an interview with Francis Everitt of Stanford University “Principal Investigator” who apparently oversaw the project you reference. He sounds like a rather pompous OXCAM professor. Not one of the best interviews I’ve heard, but, I’m in and out of my car in the afternoons, so I rarely get the full picture of these discussions.

There’s lots of other good stuff in the 75 pages of Archive.

http://sciencefriday.com/

http://www.sciencefriday.com/feeds/radio/

Here’s the link to my local Wash DC station that airs at 7pm Irish, Fridays. You can check other stations listed on the Science Friday site for alternative times to listen live on other stations.

http://wamu.org/programs/

Captain Con O'Sullivan
07-05-2011, 09:35 AM
I understand dimly that the experiment has thrown up no confounders to Einstein's theories but in your reading of the results are there any indications of support for his calculations? EDIT: Woken up a bit and reread Munnkeyman's thread title but is the experiment wide-scale enough to reinforce Einstein's calculations?

Starfire
07-05-2011, 01:20 PM
Most useful link - thank you!

Munnkeyman
07-05-2011, 02:30 PM
So, did time get squashed ?

Both time and space, as they are part of the same continuum under
general relativity..
Clocks would run faster at a higher altitude due to the lower gravitational
force.
GPS satellite clocks run approximately 40 microseconds faster per day
due to this effect.


Munnkeyman,

Given that you are a science guy, (I’m interested, but mostly don’t understand) thought you might be interested in the following links.

NPR has a daily two hour current affairs program called Talk of the Nation. On Fridays it is called Talk of the Nation – Science Friday. For me, it airs 2pm eastern, 7 pm Irish. It’s also available via itunes and RSS.

One of the segments May 6, was an interview with Francis Everitt of Stanford University “Principal Investigator” who apparently oversaw the project you reference. He sounds like a rather pompous OXCAM professor. Not one of the best interviews I’ve heard, but, I’m in and out of my car in the afternoons, so I rarely get the full picture of these discussions.

There’s lots of other good stuff in the 75 pages of Archive.

http://sciencefriday.com/

http://www.sciencefriday.com/feeds/radio/

Here’s the link to my local Wash DC station that airs at 7pm Irish, Fridays. You can check other stations listed on the Science Friday site for alternative times to listen live on other stations.

http://wamu.org/programs/

Thank you Count those are really interesting links.
I don't think he's too bad, he was okay during the press conference,
I've heard much more pompous in Ireland:).


I understand dimly that the experiment has thrown up no confounders to Einstein's theories but in your reading of the results are there any indications of support for his calculations? EDIT: Woken up a bit and reread Munnkeyman's thread title but is the experiment wide-scale enough to reinforce Einstein's calculations?

Not really wide-scale to prove all tenets of GR by a long way Capt.
The two parts, the de Sitter effect and the Lense-Thirring effect were calculations derived by the early 1920's as solutions to Einstein's theory.

This is really a proof, of what's termed gravitomagnetism, that a rotating mass produces a contribution to the gravitational field of the mass.
It's analogous to magnetism in the sense that a rotating magnet would produce a similar effect in an electromagnetic field.

There are still many more areas to be proven, such as black holes and on larger cosmological
scales i.e. does it hold water outside of the solar system.

Captain Con O'Sullivan
07-05-2011, 02:53 PM
Thanks Munnkeyman I'd be lost in all this without your explanations...

Munnkeyman
07-05-2011, 04:03 PM
Thanks Munnkeyman I'd be lost in all this without your explanations...

You're welcome, I could still fill a library with what I don't know or understand, so be wary:)