GR's Tests validity over other theories

[toe21k]

GR's Tests?

The Graces from Gravity Probe B Official Web Site:-'...essential areas of general relativity have never been checked experimentally.'

[?]:- It that Real?


http://www.superstringtheory.com/forum/socboard/messages6/99.html

 

[LURCH]

Yes. GR makes several predictions that would distinguish its validity over other theories. The curving of light in a gravitational field and orbital precession are two notable predictions that have been verrified by observation. Time dilation is another.

Some other major predictions of GR include "gravity waves" and "frame dragging", niether of which have been observed. We currently have LIGO looking for the gravity waves, and in the future http://lisa.jpl.nasa.gov/ is planned to look for them even more accurately. And of course, GP-B will test frame-dragging.

 

[toe21k]

... from Gravity Probe B 'Official' Web Site:-

Einstein's Two-and-a-Half Tests:-

'Starlight deflection proved frustratingly difficult to measure. Mercury's orbit, though better, was subject to Newtonian disturbances...'

http://einstein.stanford.edu/content/story_of_gpb/gpbsty2.html

Any Comment(s) [?]

 

[MathematicalPhysicist]

Originally posted by LURCH
Yes. GR makes several predictions that would distinguish its validity over other theories. The curving of light in a gravitational field and orbital precession are two notable predictions that have been verrified by observation. Time dilation is another.

Some other major predictions of GR include "gravity waves" and "frame dragging", niether of which have been observed. We currently have LIGO looking for the gravity waves, and in the future http://lisa.jpl.nasa.gov/ is planned to look for them even more accurately. And of course, GP-B will test frame-dragging.

here it says frame dragging has been detected in two black holes in 1997:
http://www.rdrop.com/users/green/school/framdrag.htm

btw does it mean that black hole pulls everything including space time, how can it be done i thought spacetime isn't matter and that just matter can be pulled inside a black hole?

 

[davilla]

Wow, the technology of GP-B is absolutely amazing. I could never have dreamt of the purpose of such a project, nor knowing the purpose have imagined the experiment, nor knowing the experiment have envisioned the aparatus, nor knowing the apparatus have calculated the precision, nor knowing the precision have believed the feasibility, nor believing the feasibilty have understood the myriad of cutting-edge sciences, nor understanding the science have engineered the device, let alone the a process for constructing its componenets. Imagine the cumulative brainpower required in this test of one man's theory.

I can see the headlines now: GP-B collides with man-made debris, drifts spacewards

 

[LURCH]

Originally posted by loop quantum gravity
here it says frame dragging has been detected in two black holes in 1997:
http://www.rdrop.com/users/green/school/framdrag.htm

btw does it mean that black hole pulls everything including space time, how can it be done i thought spacetime isn't matter and that just matter can be pulled inside a black hole?

RXTE found precession in the accretion disk sarounding a black hole, and this precession matched very nicely with that predicted by frame dragging, but GP-B will be more along the lines of a direct measurement.

And (althoug you probably already realize this) it's not unique to black holes, all rotating objects with a gravitational field should pull spacetime around them. GP-B is trying to measure this effect as caused by our own humble little planet.

I can see the headlines now: GP-B collides with man-made debris, drifts spacewards

If that happens, my head will probably explode !

 

[toe21k]

https://www.physicsforums.com/showthread.php?threadid=9574

 

[wolram]

dont hold your breath, frame draging would be a vindication
of one or two theories for gravity but it is tenuose and will be
shown to be a misconseption, i also doubt that ligo will give
any positive results, hope i am wrong .

 

[kx21]

...

Gravity Probe B confirmed

the 'Basic Instinct' of Nobel Prize for Physics...

https://www.physicsforums.com/showthread.php?s=&postid=105266#post105266

[?]

kx21

 

[Creator]

Originally posted by wolram
frame draging would be a vindication
of one or two theories for gravity but it is tenuose and will be
shown to be a misconseption,

Wolram...
What is your reason for saying frame dragging is 'tenuos' and why are you so confident (before experiments ) that is will be shown to be a misconception?
I.E., do so have some basis to refute Lense-Thirring ?

Creator

 

[Creator]

Originally posted by toe21k
... from Gravity Probe B 'Official' Web Site:-


http://einstein.stanford.edu/content/story_of_gpb/gpbsty2.html

Any Comment(s) [?]

For the most part... very good article, 21toes

The basic idea, as Lurch said, is to test competing relativistic theories. In order to do so Gravity Prbe B is actually testing two different predicted GR effects:

One is called the geodetic effect: At the proposed orbit the gyroscope axis is predicted by GR to precess (about 6.6 arcseconds/yr.) strictly due to its passage thru the static gravitational field of the earth; i.e., strictly as a result of passing thru the Earth's 'space-time curvature'. This is the same effect that produces the advance of the perihelion of Mercury, except in that case it is the solar 'geodetic' effect.

The 2nd effect is sometimes called the 'motional' GR effect, that is, due to the motion of mass (in this case, the rotation of the earth) and is named after its discoverers Lense-Thirring. This effect is sometimes referred to as the 'gravitomagnetic field' since it is analogous to the magnetic field (in electromagnetics), which is due to the motion of electric charge.
The precession of the gyroscope due to the motional effect is quite a bit smaller than the geodetic, being about 42 milli arcseconds/year, and requires much greater precision and technology. However, in a polar orbit the two effects are predicted to be at right angles to each other, making discrimination somewhat easier.

Creator

 

[LURCH]

Originally posted by wolram
dont hold your breath, frame draging would be a vindication
of one or two theories for gravity but it is tenuose and will be
shown to be a misconseption, i also doubt that ligo will give
any positive results, hope i am wrong .

You are probably right; the effect will be very small, and those who do not agree with GR's prediction of frame dragging will remain unconvinced. LIGO and LISA will only gather first measurements in experiments that will have to be independently verified by other means and repeatedly reinforced before the findings can be considered reliable.