# Talk:Gravitoelectromagnetism/Archive 2

## Clarification?

I know this is a long shot, but I'm going to ask anyway. I read the article and it sounds to me like if you apply a force to a mass that would cause it to accelerate, the GEM analog of self-inductance will cause it to accelerate faster than you would expect classically. That sounds wrong to me. Where does the extra energy come from?

I guess I should explain why I think this. In electromagnetics, self-inductance has the opposite effect (it resists acceleration), but the sign change appears to flip this effect around backwards. Consider a mass current flowing away from a clock face, toward the person looking at the clock. Accelerating this flow would increase J, thus increasing the surrounding B in the clockwise direction (because of the sign-changed 4th equation). By the third equation, this creates an E-field in the direction we just said the particle is accelerating. By the force equation, the particle accelerates even more than it would have originally.

Please help, if you know what I'm doing wrong. Other than being physics-impaired, I mean. X-| Xezlec 23:49, 22 April 2007 (UTC)

It does accelerate faster. Another way of looking at the same thing is that it accelerates faster due to having reduced inertia from the gravitational binding energy. 69.140.12.180 (talk) 15:31, 2 April 2009 (UTC)Nightvid
A more intuitive approach might be to think of the gravitoelectric field around the mass as having negative energy density (which in the GEM model it will have, analogous of the EM field energy density, but with a negative constant). This is essentially what is referred to above as gravitational binding energy. Quondum (talk) 16:35, 11 September 2011 (UTC)

Energy should still be conserved if it accelerates faster then it decelerates faster as well.

## Citations

To ensure uniform appearance and for other reasons, in future please use citation templates. Please bear in mind that this is an encyclopedia article, not a review article in RMP. Don't attempt to list every paper which has ever appeared. Don't list your own papers (very bad form!). Don't list paper A if there is a better paper B, particularly if B cites A. Do list review good papers like Mashhoon 2003. Do think carefully and try to keep the list to a half dozen primary sources. For example, do consider removing A and B if review R cites them. TIA ---CH 01:03, 27 March 2006 (UTC)

## From SI to Planck: Question

The last 2 paragraphs of section 1.1 may be wrong. The fourth Maxwell equation in SI units is:

${\displaystyle \nabla \times \mathbf {B} =\mu _{0}\mathbf {J} +\mu _{0}\epsilon _{0}(\partial \mathbf {E} /\partial t)=c^{-2}((\mathbf {J} /\epsilon _{0})+\partial \mathbf {E} /\partial t)}$

In Planck units:

${\displaystyle \nabla \times \mathbf {B} =4\pi \mathbf {J} +\partial \mathbf {E} /\partial t}$

Planck and CGS units normalize the Coulomb force constant, (4πε0)-1, to 1. The above equation in Planck units makes sense if such units normalize μ0 to 4π, a normalization I cannot confirm. Do CGS units normalize μ0 to 1? How can 4π be eliminated from Maxwell's equations? If you can answer these perplexities, don't reply here; instead, please edit the last 2 paras of section 1.1.202.36.179.65 17:52, 29 March 2006 (UTC)

even though Planck units are a neat topic that i have interest in, i am not sure of the pedgagical advantage in putting all that in this article. we should just point out, in comparison to E&M, that charge is replaced by mass, charge density by mass density and ${\displaystyle {\frac {1}{4\pi \epsilon _{0}}}\leftarrow -G\ }$. true, if you use rationalized Planck units (same as Planck units except ${\displaystyle 4\pi G\ }$ is normalized to one instead of ${\displaystyle G\ }$), then the GEM equations look just like Maxwell's Eqs. except for a minus sign where there is charge or charge density. Rbj 21:56, 29 March 2006 (UTC)

Cleaning up In Planck units table of equations: I would like some opinion on the question of the equations "in Planck units". The text immediately above the table of equations says the equations are the same with −G replacing ​14πε0, then the table does not mirror this, potentially creating the impression that the iota tracks an essential difference between the EM and GEM cases, whereas the replacement makes the equations fully identical without the iota. Since Planck units per se are not significant here, would it not be much clearer if rationalized Planck units in which we set 1 = ε0 = −​1G? The significant point is that the equations then become identical, and do not need the silly iota that is there only because G has been normalized to be positive. The table cound be revised, or a second column for these rationalized units could be added: Quondum (talk) 13:26, 15 September 2011 (UTC)

 Common Structure of the Maxwell and GEM Equations with normalization 1 = c = ε0 = −​1⁄4πG. ${\displaystyle \nabla \cdot \mathbf {E} =\rho }$ ${\displaystyle \nabla \cdot \mathbf {B} =0}$ ${\displaystyle \nabla \times \mathbf {E} =-\partial \mathbf {B} /\partial t}$ ${\displaystyle \nabla \times \mathbf {B} =\mathbf {J} +\partial \mathbf {E} /\partial t\ }$
I like rationalized Planck units. I've always considered c = ħ = 4πG = ε0 = 1 to be the most natural system of units possible when one looks at the equations of interaction without considering the specific quantitative properties of any prototype object or particle that would have to be selected on some arbitrary basis. And what you have above is Maxwell's equations as expressed in these rationalized Planck units. No funky factors of 4π anywhere.
But the article has to be about what is commonly in use. If we replace that table with one using rationalized Planck units, let's be sure to spell that out with something equivalent to "c = ħ = 4πG = ε0 = 1". 71.169.184.192 (talk) 16:40, 16 September 2011 (UTC)
The point about rationalized Planck units was already made above my Rbj. My point is that the object of the section is to show the similarity of the GEM and EM formulae, and that this can be best done by explicitly defining εg = −​14πG (including the sign in the constant rather than in the formula). I also like rationalized units, but I can see that this subsection is entirely irrelevant to the article and is actually diverting attention from my attempt to get rid of the iota. I suggest that the subsection In Planck units be removed entirely, and that the table above it in section Equations be replaced by the following
GEM equations Maxwell's equations
${\displaystyle \nabla \cdot \mathbf {E} _{\text{g}}={\frac {\rho _{\text{g}}}{\epsilon _{\text{g}}}}\ }$ ${\displaystyle \nabla \cdot \mathbf {E} ={\frac {\rho }{\epsilon _{0}}}}$
${\displaystyle \nabla \cdot \mathbf {B} _{\text{g}}=0\ }$ ${\displaystyle \nabla \cdot \mathbf {B} =0\ }$
${\displaystyle \nabla \times \mathbf {E} _{\text{g}}=-{\frac {\partial \mathbf {B} _{\text{g}}}{\partial t}}\ }$ ${\displaystyle \nabla \times \mathbf {E} =-{\frac {\partial \mathbf {B} }{\partial t}}\ }$
${\displaystyle \nabla \times \mathbf {B} _{\text{g}}={\frac {1}{\epsilon _{\text{g}}c^{2}}}\mathbf {J} _{\text{g}}+{\frac {1}{c^{2}}}{\frac {\partial \mathbf {E} _{\text{g}}}{\partial t}}}$ ${\displaystyle \nabla \times \mathbf {B} ={\frac {1}{\epsilon _{0}c^{2}}}\mathbf {J} +{\frac {1}{c^{2}}}{\frac {\partial \mathbf {E} }{\partial t}}}$
where:
Quondum (talk) 09:44, 17 September 2011 (UTC)

## Gravitomagnetic explanations for relativistic jets

A paragraph with references was added to present the dramatic ramifications of jet analyses for gravitomagnetism. Tcisco 03:43, 13 April 2007 (UTC)

## Comparison with electromagnetic force

The gravitational attraction between protons is approximately a factor of 1036 weaker than the electromagnetic repulsion. This factor is independent of distance, because both interactions are inversely proportional to the square of the distance. Therefore on an atomic scale mutual gravity is negligible. Even so, the main interaction between everyday objects and the Earth and between celestial bodies is gravity, because at this scale matter is electrically neutral. This means that there is an equal number of positively charged particles in the universe to negatively charged particles. For example, there aren't any positively charged planets that zoom into negatively charged planets. This means that gravity dominates the universe even though it is the weaker force. However, to show the delicate balance of gravity over the electromagnetic force, given two bodies if even there were a surplus or deficit of only one electron for every 1018 protons and neutrons this would already be enough to cancel gravity (or in the case of a surplus in one and a deficit in the other, double the force of attraction).

Though the force of gravity dominates the visible macro universe, the main interactions such as fusion between the charged particles in cosmic plasma, of which the sun is composed and which make up over 99% of the universe by volume, are due to the nuclear forces. In terms of Planck units, the charge of a proton is 0.085, while the mass is only 8×1020. From that point of view, the gravitational force is not small as such, but because masses are small. The relative weakness of gravity can be demonstrated with a small magnet picking up pieces of iron. The small magnet is able to overwhelm the gravitational effect of the entire Earth. Even though gravity is relatively weak, the small gravitational interaction exerted by bodies of ordinary size can fairly easily be detected through experiments such as the Cavendish torsion bar experiment.

• Jefimenko, Oleg D., "Causality, electromagnetic induction, and gravitation : a different approach to the theory of electromagnetic and gravitational fields". Star City [West Virginia] : Electret Scientific Co., c1992. ISBN 0917406095
• Heaviside, Oliver, "A gravitational and electromagnetic analogy". The Electrician, 1893.

J. D. Redding 17:30, 14 April 2007 (UTC)

## Removed phrase

I removed the text:

Frame-dragging is often mentioned as a gravitomagnetic effect, but the Lense-Thirring effect (precession) may be a more appropriate example.

This sounds like a normative opinion, and is unreferenced. It is also somewhat confusing, in that the Lense-Thirring effect is a type of frame-dragging, according to that article. If I'm remembering my E&M correctly, I think both accelerational and rotational frame-dragging have analogies in magnetism, so I don't know why one would be a better example than the other, but if I'm wrong, a reference would be needed to support this claim. -- Beland 00:11, 21 April 2007 (UTC)

## Removed cleanup, expert needed tags

I removed the "expert needed" tag, because we apparently already have one. It might not be a bad idea to explicitly declare that a certain version has been fact-checked by an expert and judged to be without obvious error.

If you feel there are remaining "cleanup" or "expert needed" items, please list them explicitly, because they are not obvious. There were mentions in the talk archive about a "todo" list, but I could not find it, so I assume all the tasks that were listed on it have been completed. -- Beland 00:15, 21 April 2007 (UTC)

## Diagram request

This article does a pretty good job explaining the concepts involved in words and equations, but many people would be assisted by visual aids. It would be useful to illustrate the "moving X creates a Y field" concept, and perhaps some of the toroidal fields mentioned in the "higher order effects" section. -- Beland 00:18, 21 April 2007 (UTC)

## The Units

The units need to be synchronized so that the magnetic permeabilty and the universal gravitational constant lead to the speed of light for gravitomagnetic radiation. (201.95.155.237 12:32, 8 May 2007 (UTC))

i think they are consistent as such. r b-j 14:42, 8 May 2007 (UTC)

No they are not. These equations involve the universal gravitational constant in Ampère´s law. If we combine the two curl equations to obtain the gravitomagnetic wave equation, the presence of the gravitational constant will destroy the link to the speed of light. You need to use magnetic permeability just as is the case in the electromagnetic equivalents. Permeability lies at the heart of magnetism and it is not catered for in this hypothesis. It needs to be catered for in order to give any credibility to the concept of gravitomagnetism. Dr. Francesco Hidalgo, Buenos Aires, 12th May 2007 (200.43.23.50 20:21, 12 May 2007 (UTC))

Just for my own information, the permeability of free space that you say lies that the heart of magnetism, is, as best as I can tell, a defined scaler that comes about solely because of how the unit of current (and consequentially the unit of charge) was defined. ${\displaystyle \mu _{0}\ }$ is no measured property of free space. Since Maxwell's Equations can be written in such a way to exclude any mention of ${\displaystyle \mu _{0}\ }$ (by using only c and ${\displaystyle \epsilon _{0}\ }$, the first is the speed of propagation and the second is the inverse of the Coulomb force constant), so also can the GEM equations be written so to exclude any ${\displaystyle \mu _{0}\ }$ symbol, by putting the GEM equations in terms of the speed of propagation, c, and the Newton force constant, G. One might argue that the speed of propagation is different for gravitational interaction than it is for electromagnetic interaction, but there is no need to use the specific "permeability" symbol in GEM, just as there is no such need in ME. 207.190.198.135 17:53, 11 July 2007 (UTC)

## Gravitomagnetic monopoles

Does any theory predicts gravitational analogue of magnetic monopoles? Their existence would make GEM equations more symmetric just as existence of magnetic monopoles would make Maxwell's equations more symmetric. If there is such theory, it should be mentioned in the article. --193.198.16.211 08:15, 11 June 2007 (UTC)

Yes the treatise on gravitomagnetism predicts analogue of magnetic monopoles.
Can you give any reference for gravitomagnetic monopoles? What inertial properties would object with gravitomagnetic charge have? Obviously, gravitomagnetic dipole, would be something with angular momentum, and true one would be elementary particle with spin, but what about monopole? It seems that it would have some rather interesting and unusual inertial properties. --83.131.23.165 10:40, 11 July 2007 (UTC)

## Reed College Senior Thesis Description

I wrote a thesis developing the gravitational analog to the Maxwell's equations, Brown, D.R., "A Gravitational Analog to Electromagnetism" as a Reed College senior thesis in 1968. Since Maxwell's equations can be fully developed from the Coloumb equation and Special Relativity, one can use the same formalism to develop the gravitational equations. Note that since this demonstrates that magnetic fields derive from relavisitically transformed electric fields, the question of magnetic monopoles in either description would appear to be ruled out. This work was never published in the literature, but a copy exisits in the Reed College thesis room, and with me. Please contact me if you have further interest.

Dr. D. R. Brown, drphysic@juno.com —Preceding unsigned comment added by 24.20.192.49 (talk) 17:30, 24 February 2008 (UTC)

## Has anyone succeeded in formally deriving the Lense-Thirring force from the GEM theory described here in detail?

Yes, you can use the Lorentz transformation to directly derive gravitomagnetism laws, search the treatise on gravity and gravitomagnetism in GOOGLE.

I found the following phrases in the suggested article

"Our approach is in accordance with the model published by Maxwell in 1891, in his third edition of Treatise on Electricity and Magnetism. It is by honest analogy to mechanics that Maxwell elaborated the Treatise on Electricity and Magnetism. By analogy to Treatise on Electricity and Magnetism done by Maxwell, it is logical to elaborate the Treatise on Gravity and Gravitomagnetism by using Lorentz Transformation as a mathematical tool without forgetting the specificity of gravity, thus masses of the same sign attract each other. By symmetry, logically masses of opposite signs should repulse each other but this is just a conjecture."

But you can't get gravity from the modified Maxwell's equation. I don't think that is the real answer to the problem. I mean can you get the gravitomagnetism directly from general relativity? —Preceding unsigned comment added by 70.128.182.230 (talk) 16:32, 3 April 2008 (UTC)

Google search for dipole gravity. Dipole gravity is the true gravitomagnetism derived directly from general relativity. It reduces into the Lense-Thirring force near the center of the rotating spherical shell. —Preceding unsigned comment added by 70.128.182.230 (talk) 10:58, 5 April 2008 (UTC)

You don't modify the Maxwell equations, you use the Lorentz transformation de derive gravitomagnetism. You'll find that what you get is in accordance with the astronomical observations. Black Whole bipolar jets can be easy explained by considerating the gravitomagnetic field build in the poles by mass currents. It's a straight forward approach that gives coherent results. It simplifies everything —Preceding unsigned comment added by 195.6.25.114 (talk) 15:27, 7 April 2008 (UTC)

Special relativity itself is not a theory of any kind of a force. It is a well known fact that Wheeler's gravitomagnetism is not based on general relativity, which only means that it is a faulty theory of gravity which has nothing to do with the actual gravity. It's lamentable to see that GP-B experimental result is being analyzed using this nonsensical theory of gravitomagnetism. I don't know what makes them think that they are testing general relativity when they are comparing the data with Wheeler's gravitomagentism. Can you clearly see my point?

The true gravitomagnetism can only be found from general relativity. And dipole gravity proved it is the true gravitomagnetism by successfully deriving the Lense-Thirring force at the center of the rotating sphere. —Preceding unsigned comment added by 70.244.207.137 (talk) 09:13, 11 April 2008 (UTC)

As you can see the Treatise on Gravity and Gravitomagnetism describes linear vector gravity, the results are in accordance with the astronomical observatins, the facts are there, they remain the keystone on which the stability of a theory must be tested —Preceding unsigned comment added by 195.6.25.114 (talk) 13:10, 2 May 2008 (UTC)

Why should we bothered by a theory that has not been tested rigorously? The conventional gravitomagnetism(based on Lorentz invariance) is not "general relativity" period. Please read the paper on dipole gravity. It is the only theory that derives the true Lense-Thirring force. Seeing is believing.

According to the conventional gravitomagnetism, one of the poles of the earth should have less gravity than the other pole, which has never been verified.

Also, the black hole should emit a long jet from one pole but not as long from the other one. This has not been true with the observation. Wheeler's and others gravitomagentism is a false theory which has nothing to do with the reality. Stick to general relativity and all will be fine. —Preceding unsigned comment added by 64.149.161.230 (talk) 07:42, 6 May 2008 (UTC)

In the Treatise on Gravity and Gravitomagnetism, in part one, page 45, you can learn how to to calculate the gravitomagnetic field by using mass currents, in the Earths North Pole and South Pole. The value is exactly Bg = 1x 10 E-14 radians /second. This value is mentioned by WIKIPEDIA (see gravitomagnetism). According to Treatise on Gravity and Gravitomagnetism the two poles have the same gravitomagnetic and gravity field. And as you can also learn in the Treatise on Gravity and Gravitomagnetism, in part two, page 16, how the bipolar jets are produced in the Black Whole North and South Poles. This is in conformity with the scientific observation. Please take time to verify your claims before you publish them because the facts are there, they remain the keystone on which the stability of a theory must be tested. —Preceding unsigned comment added by 195.6.25.114 (talk) 09:16, 20 May 2008 (UTC)

If the ring in rotation creates a gravitomagnetism, which side becomes the north pole and which side the south pole? And what determines the polarity? Does it depend on clockwise or counter clock wise rotation? The designation of the north and the south may be arbitrary but effectively, one side must be an attractive and the other side has to be a repulsive gravity pole, but the geometry of the ring doesn't give any clue on which side will be repulsive and which side will be attractive since they are identical. The rotating hemispherical object makes clear of this question. The domed side and the flat side of the rotating hemisphere has the opposite polarity to each other.

If you can not tell which side of the rotating ring will be attractive and/or repulsive, what's the point of calling it a "gravitomagentism"? —Preceding unsigned comment added by 70.246.92.167 (talk) 07:28, 12 June 2008 (UTC)

Repulsion is with respect to another pole, North and South pole are just taken arbitrary, it's just a convention, in the Treatise on Gravity and Gravitomagnetism part one page 45, the direction of the rotation of the Earth has been taken to be positive and the gravitomagnetic North corresponds to geographical North. The basic principle is that opposite poles attract each other and like poles repulse each other. North and south are taken arbitrary. —Preceding unsigned comment added by 195.6.25.114 (talk) 06:46, 17 June 2008 (UTC)

Yes, you can look at the sample problem at the end of my paper here: http://aforrester.bol.ucla.edu/educate/Articles/Derive_GravitoEM.pdf (Unfortunately, it's not pedagogical right now; I'll have to correct that later.) Zeroparallax (talk) 01:25, 23 April 2010 (UTC)

## Units?

I am changing the symbols B and E in the equations in the section "comparison with electromagnetism" to add the subscript "g", since they are not, in fact, B and E, but are rather the gravitational analogues to B and E. Also, this section has the following text: "In the literature, all instances of B in the GEM equations are multiplied by 1/2, a factor absent from Maxwell's equations. This factor vanishes if B in the GEM version of the Lorentz force equation is multiplied by 2, as shown above." If all references in the literature have the factor 1/2 added, I'd like to know why this article doesn't include that factor as well. Geoffrey.landis (talk) 16:15, 14 August 2008 (UTC)

It seems there is a unit inconsistency between the main GEM equations and the example of a rotating object. In the main equations, Bg has units of m/s^2. In the example, Bg has units of 1/s. —Preceding unsigned comment added by 76.23.236.214 (talk) 01:36, 3 September 2008 (UTC)

Yes this is true, there is a unit inconsistency between the main GEM equations and the example of a rotating object,check for coherent units of Bg in the treatise on gravity and gravitomagnetism, it is 1/second (hertz thus frequency). —Preceding unsigned comment added by 195.167.194.180 (talk) 13:33, 14 November 2008 (UTC)

## Solenoidal Gravity

It says in the main article,

${\displaystyle \nabla \cdot \mathbf {B} _{g}=0\ }$

And where do we find this solenoidal gravitational field? David Tombe (talk) 21:15, 18 November 2008 (UTC)

I don't see any difference between this and ordinary electromagnetism. It's got the same constants. David Tombe (talk) 11:02, 19 November 2008 (UTC)

## Factor of two error in Lorentz force law?

I think the cross-product term in the Lorentz force law equivalent should have a factor of 4, not 2. It looks as if when factor of 1/2 was applied, it wasn't applied everywhere consistently. Jonathan A Scott (talk) 19:54, 19 November 2008 (UTC)

I'm not even sure what reasoning was initially applied in order to establish the so-called Lorentz force equivalent listed in the main article. There is an already established relationship between vorticity and angular velocity for situations in which a fluid rotates as one single entity without any graduation. That relationship is given by B = 2ω where B is vorticity and ω is angular velocity. This relationship can provide a direct link between the vXB term in electromagnetism and the Coriolis force. The Coriolis force is the obvious gravitomagnetic equivalent to F = qvXB. If space where considered to rotate as one rigid entity, then there would be at least some rationale behind the expression given in the main article. But it all comes down to what we understand by B in connection with a gravitational field. It must clearly be something to do with the rotation of space. If we interpret B as being the angular velocity of rigid space that rotates on the large scale, then the factor of 2 would be correct. But if we interpret B as being the vorticity of a dynamic space, then we would want to get rid of the factor of 2. I cannot however see any justification for ever involving a factor of 4. David Tombe (talk) 11:16, 20 November 2008 (UTC)

Introducing the ${\displaystyle \mathbf {A} _{g}}$ vector would suggest that we need to get rid of the factor of 2 altogether, rather than changing it to a 4. Consider that ${\displaystyle \mathbf {E} _{g}}$ in general is,

${\displaystyle \mathbf {E} _{g}=-{\frac {1}{c}}({\frac {\partial \mathbf {A} _{g}}{\partial t}}-\mathbf {v} \times \mathbf {B} _{g})}$

Then taking the curl, we get,

${\displaystyle \nabla \times \mathbf {E} _{g}=-{\frac {1}{c}}({\frac {\partial \mathbf {B} _{g}}{\partial t}}+({\mathbf {v} \cdot \nabla })\mathbf {B} _{g})=-{\frac {1}{c}}{{d\mathbf {B} _{g}} \over dt}}$

This relationship between the total time derivative and the partial time derivative, in relation to Faraday's law, is found in 'J.A. Stratton, Electromagnetic Theory, (McGraw-Hill, New York, 1941), in 23, Chapter 5.

This would suggest that we are not dealing with a rotation of space on the large scale. David Tombe (talk) 21:31, 20 November 2008 (UTC)

## The Kepler Issue

In matters to do with gravity, we must not forget Kepler's first law. That of course introduces centrifugal force into the equation, which will of course be an irrotional term. And we must further remember that any new curl terms, as speculated in the main article, will cause a breakdown of Kepler's second law. David Tombe (talk) 05:20, 21 November 2008 (UTC)

## Justification for the displacement current term

In electromagnetism, there are two quite different justifications for displacement current depending on whether we are dealing with a vacuum or a dielectric. What is the explanation for displacement current in gravitomagnetism in the Ampère's Circuital Law and Biot-Savart law equivalent equations? David Tombe (talk) 05:17, 23 November 2008 (UTC)

## "Fictitious Forces" and GEM Resources

I don't have time to correct the article right now, but here's my comment. The use of the term "fictitious force" in this article to refer to the magnetic force and the gravito-magnetic force is incorrect -- I think the author actually meant "non-fundamental" force. The magnetic force can be explained as a delayed effect of the electric force, since the particle that mediates the force, the photon, travels at a finite velocity. So the magnetic force is actually merely a component of the electric force and in that sense can be seen as non-fundamental. Examining the electric force in different reference frames will change the portion of the electric force that is magnetic and the portion that is "non-magnetic", but both of these portions are actual forces caused by the photon's interaction with charged particles -- they are not "fictitious" forces. A fictitious force is an apparent force that is actually due to acceleration and inertia and has no mechanism (other than a mechanism you might propose for inertia itself).

I wrote a paper that derives the gravito-electromagnetic (or gravito-magnetic) equations directly from the Einstein field equations of gravity. It's here: http://aforrester.bol.ucla.edu/educate/Articles/Derive_GravitoEM.pdf Unfortunately, it's not pedagogical; someday I'll have to improve it so it's more understandable. It also has a sample problem involving the Lense-Thirring effect. Zeroparallax (talk) 01:21, 23 April 2010 (UTC)

hmmm Indeed the electric field and magnetic field are less fundamental than the 4-vector potential no? So if you want find a "source" of fields, it is rather this potential than the electric field. To say the electric field is more fundamental means the rest is more fundamental than motion, that is not true since their definition depend of an observation frame transformation. And in GR gravitational acceleration is locally equivalent to inertial acceleration, thus there are no real forces and inertial forces, gravitation is an inertial force.Klinfran (talk) 08:09, 13 May 2010 (UTC)
I have removed the reference to fictitious force; it seems to be making a vacuous point that has no place in the context. It diverts attention from the very real gravitational effects (including locally measurable ones, such as tidal effects and, theoretically at least, gravitational radiation), which cannot be formulated globally merely in terms of an accelerated frame of reference. Quondumtalkcontr 11:39, 1 December 2011 (UTC)

## dimensions

Hello, as the acceleration generated by the gravitomagnetic field is ${\displaystyle \mathbf {v} \wedge \mathbf {B_{g}} }$ it is very doubtful that dimensions of the gravitomagnetic field are m/s2 Klinfran (talk) 07:55, 13 May 2010 (UTC)

Dimensions are fixed now. --antiXt (talk) 11:32, 29 May 2010 (UTC)

According to the brief review article by Mashhoon, the units for the fields E and B should be acceleration. In physics, one commonly uses the relativistic speed beta, v over the speed of light c. The issue looks like the Lorentz force was not written correctly, is should be ${\displaystyle F_{m}=m(E_{g}+{\frac {\mathbf {v} }{c}}\wedge \mathbf {B_{g}} )}$. That has the right units and is consistent with the paper and conventions seen in relativity. Sweetser (talk) 03:52, 6 July 2010 (UTC)

## Equations are not consistent with two cited sources (1 author)

B. Mashhoon (2003). "Gravitoelectromagnetism: a Brief Review", eq. 1.9, writes the GEM Gauss's and Ampere's laws with POSITIVE charge density rho and a positive current density J. Masshoon's other cited paper, "Gravitomagnetism and the Clock Effect" follows the same practice. The paper by Lano and Agop et al. did use negative charges. Gravitomagnetism is considered a "toy" theory because it must have masses that have positive and negative charge, just like EM (he does this on page 5 of the brief review article). Because the field strength tensor is anti-symmetric, the interaction must be described by a spin 1 field where like charges repel. From the article, I did not get a sense that professionals take the subject with a large grain of salt because gravitomagnetism is inconsistent particularly with regard to spin. I understand why people prefer the minus signs on the charges: that way the Gaussian law reduces to Newton's law and like charges attract in the potential form. Maxwell's equations are a spin 1 field and so is gravitomagnetism, which is the source of the problem with the approach. Sweetser (talk) 03:35, 6 July 2010 (UTC)

## String of references in Equations section

Is there a good reason for having 5 references for the table with the GEM equations? It appears that lots of people have derived them independently, as one would expect, so that it's not really necessary to cite them all. Years ago they were even mentioned by name. [1] Or are the references all of questionable value (like the Fedosin book, which appears to be self-published), so that it's impossible to select a good one? Hans Adler 07:45, 11 April 2011 (UTC)

## The role of pressure?

In general relativity, the trace of the stress-energy tensor ${\displaystyle T^{\mu \nu }}$ is, as far as I can tell (I'm no fundi), the source of the Newtonian/gravitoelectic field, and would thus play the role of density in the GEM equations. Is it not worth clarifying this in the article? This is relevant, even in the weak-field limit - take for example the GEM field generated by an intense laser beam. The longitudinal pressure in the beam generates a radial ${\displaystyle E_{q}}$ field similar to that of the energy/mass of the beam, making the resulting radial field (at a guess) a factor of 2 larger than if the mass/energy of the beam alone were used as the density ${\displaystyle \rho _{g}}$ in the equations. Quondum (talk) 12:14, 7 September 2011 (UTC)

After a little reading, I've concluded that the high relative pressure (meaning pressure is comparable to energy density when units are made the same by dividing by c2) of EM fields (even the static magnetic field around a bar magnet) are typically explicitly excluded in the references. Thus my suggestion probably has no place in the article. I will replace it with the observation that the section Equations gives only strong gravity as an exclusion, but should add high pressure and high (near light) speeds of the source. I am not going to make this change, not being familiar enough with the topic. Quondum (talk) 08:08, 9 September 2011 (UTC)

## Field direction

It seems that in the picture "Gravitomagnetic field due to angular momentum.svg" line of field H are not correct directed. Their direction are opposite. 95.29.30.167 (talk) 05:31, 13 September 2011 (UTC)

Thank you very much for noticing, I fixed the direction now. I havn't even looked at this article for like a month, so I didn't notice you had pointed that out. Maschen (talk) 11:44, 22 October 2011 (UTC)

## Extension to EM analogy of energy density, pressure etc.

Direct and intuitive analogies arise from the analogy of GEM to EM, namely the energy density, the Poynting vector and similar energy/force/momentum concepts. Mentioning these (even in the absence of reference material) would serve to highlight further similarities or the lack of research on the subject. For example, the Eg field has an intuitively sensible energy density in the classical view, which happens to be negative and is easily derived: if a very distant masses are brought together, their fields superpose, and energy (that would have become kinetic energy of falling together) is removed from the system. In the GEM formulation, this energy comes from the Eg increasing and a square-relationship between (negative) energy density and the field strength. A similar energy density would apply for the Bg field, though would not be as simple to derive, and who knows what constants of 2 or 4 would bedevil it. And similar to the EM case, there will be positive and negative pressures associated with static (and dynamic) GEM fields - in the EM case there is a negative pressure in the direction of a field, and an equal but positive pressure in both perpendicular directions. In the GEM case, the signs for the pressure are presumably changed for the parallel and perpendicular directions. Is anyone aware of papers that address this, and if there is a dearth, is anyone in favour of pointing out in the article that this topic has not been addressed? Quondum (talk) 07:54, 30 September 2011 (UTC)

## Inappropriate section added by 92.100.176.81

The recent section General Concept being added by 92.100.176.81 is liable to be deleted in its entirety. The article is about the form of gravitoelectromagnetism, aka linearised weak field gravity, and its similarity with electromagnetism. The additions are all entirely off-topic. This IP appears to be using this article as a scratch page for putting together a variety of pet ideas, which is entirely inappropriate on Wikipedia. Quondum (talk) 12:11, 11 October 2011 (UTC)