anti-gravity from spinning gravito-magnetic field?

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alexjrgreen
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Joined: Thu Nov 13, 2008 4:03 pm
Location: UK

Post by alexjrgreen »

pfrit wrote:To consider "Aether" to be the same thing as space-time requires a pretty silly "Aether".
Brian Greene called his book on string theory "The Fabric of the Cosmos".

If space-time was empty it wouldn't have virtual particles popping in and out of existence within it. Not so much silly as deeply strange...
Ars artis est celare artem.

rcain
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Post by rcain »

pfrit wrote:To consider "Aether" to be the same thing as space-time requires a pretty silly "Aether".
..well, then, dont. (whatever a 'silly' aether is). i would suggest 'observation', or more precisely 'measurement' is what requires a frame of reference, not nature.

pfrit
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Joined: Thu Aug 28, 2008 5:04 pm

Post by pfrit »

rcain wrote:
pfrit wrote:To consider "Aether" to be the same thing as space-time requires a pretty silly "Aether".
..well, then, dont. (whatever a 'silly' aether is). i would suggest 'observation', or more precisely 'measurement' is what requires a frame of reference, not nature.
Yes, but you can't mearure the speed of a single photon. It has to be measured against a second point. And I like calling Aether silly...
What is the difference between ignorance and apathy? I don't know and I don't care.

DeltaV
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Joined: Mon Oct 12, 2009 5:05 am

Post by DeltaV »

I like the roto-elastic aether theory of MacCullagh:

http://maxwell.byu.edu/~spencerr/phys442/history.pdf

"1839 - James MacCullagh invents an elastic aether in which there are no longitudinal waves. In this
aether the potential energy of deformation depends only on the rotation of the volume elements and not on
their compression or general distortion. This theory gives the same wave equation as that satisfied by E and
B in Maxwell’s theory.

1839 - William Thomson (Lord Kelvin) removes some of the objections to MacCullagh’s rotation theory
by inventing a mechanical model which satisfies MacCullagh’s energy of rotation hypothesis. It has spheres,
rigid bars, sliding contacts, and flywheels."

Giorgio
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Location: China, Italy

Post by Giorgio »

rcain wrote:
Giorgio wrote:
rcain wrote:... whether wave-like or not, a related observation (and a question that has always intrigued me), the effects of gravitation do now appear to 'propagate' at the speed of light +/- 20%:: http://www.nrao.edu/pr/2003/gravity/
I do not agree, their test just proved that radio waves are bended by a gravitational field. At the most they proved that light moves at the "speed of light", but this experiment gives no clues in regards to the speed of gravity.
thats what i thought at first, but reconsidered, i conclude they must have made reference to the 'rate' of bending (dt) relative to movement/acceleration of jupiter. otherwise, i agree their conclusions would not make sense.
I found this extremely interesting webpage:
http://physics.wustl.edu/cmw/SpeedofGravity.html

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# In all calculations of the effects of finite propagation speed (electrodynamics, gravitational waves), for slowly moving sources, the first non-trivial effects appear at order (v/c)^2, NOT at first order (v/c), which is what Kopeikin claimed
# If you're working to only the first order in v/c, then all that counts is the uniform motion of the planet, Jupiter (its acceleration about the sun contributes a higher-order, unmeasurably small effect). But if that is the case, then the principle of relativity says you can view things from the rest frame of Jupiter. But in this frame, Jupiter's gravitational field is static, and the speed of propagation of gravity is irrelevant.
# A detailed calculation of the effect was done by Clifford Will (here), in a model of gravity in which the speed of gravity can be different from that of light, and showed explicitly that, at first order in (v/c), the effect depends on the speed of light, not the speed of gravity, in line with intuition.
-------------------------------------------------------------------------------------

Lot of stuff to read during the weekend, but seems like they indeed measured speed of light and not gravity.

rcain
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Post by rcain »

Giorgio wrote:...
I found this extremely interesting webpage:
http://physics.wustl.edu/cmw/SpeedofGravity.html
...
Good find. Thanks Gorgio. Certainly looks like the auguments are stacking up against the NRAO reasoning then. Though they still seem to be defending their position.

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