I've been sitting on the sidelines (too busy to post with my Mother in town for her birthday), and watching this develop into a flamefest. At the risk of making ALL parties mad at me, let me jump into the fray here.

This thread has been an exercise in miscommunication from the start. I'm not a mindreader, but I have a pretty clear idea what people were thinking based on their posts (after all, language should be able to express our thoughts with reasonable accuracy, or what's the point?). If you feel I am putting words in your mouth, just say so, and I'll immediately apologize.

Here's how it looks to me:

shalayka posted that planets in the solar system radiate gravitational waves away from the sun, in order to support the point that the gravitational potential is not necessarily isotropic. shalayka never stated what specifically caused this radiation.

AlphaNumeric responded that shalayka was wrong, and to support his point stated that spherically symmetric systems do not radiate gravitationally, that anisotropy is required for gravitational radiation, that planets have equatorial bulges due to rotation, that these bulges cause them to emit gravitational radiation, that the direction of the radiation is controlled by the nature of the anisotropy, and that it is not directed away from the sun.

Both of these posts require major surgery, I'm afraid.

It became clear later that shalayka was discussing gravitational radiation due to the planet's orbital motion around the sun. By stating that the PLANET radiated gravitational waves, he did not explicitly associate the waves with the earth-sun system, which led AN to think he was talking about radiation due to the planet itself. Considering the planet ALONE as the gravitational wave source, such waves could only come from its rotation, which led to AN's making several points about isotropy. This was the first key miscommunication.

However, each post separately has other problems. It looks like AN was initially responding to shalayka's assertion that planets radiate gravitational waves away from the sun, that this was the main point he set out to correct. However, as is his usual style, he baldly stated that shalayka was wrong, then gave commentary, which did not clarify precisely where he thought shalayka was wrong. This left AN's post partly responding to something shalayka actually said ("away from the sun") and partly to something AN thought shalayka meant ("planets radiate").

Now both of these things are actually wrong, so AN was certainly correct in trying to set shalayka straight on them. Let's look at them separately, instead of all muddled up: As to the direction of the radiation, shalayka later stated that it was analogous to braking radiation. This is certainly reasonable, but braking radiation removes energy from an accelerated particle, and hence MUST be directed along the velocity of the particle, rather than opposing the direction of acceleration, so as to carry away forward momentum and also so as to do negative work on the particle. Dropping back from relativity into a Newtonian framework shows clearly that this must be true for gravitational radiation as well, since the same considerations of momentum and energy apply. The braking gravitational radiation is therefore emitted tangent to the planet's orbit, not away from the sun. Of course, AN couldn't give this explanation, because he thought shalayka was not referring to radiation due to orbital motion.

(BTW, when considering the earth-sun SYSTEM, the gravitational radiation clearly causes a loss of angular momentum. The radiation is due to the rotating quadrupole moment of the earth-sun system. The far field radiation pattern can be analyzed based on this quadrupole source, but the near field cannot. The near field pattern shows up as the braking radiation of the earth and that of the sun, which together sum up to give the quadrupole radiation in the far field limit.)

In short, shalayka made one statement that was wrong, and one that seemed wrong.

Unfortunately, AN's responses have several misstatements, which in turn gave shalayka something to jump on in response. AN's statement that a planet's equatorial bulge is what causes it to emit gravitational waves is simply wrong. Although it is no longer spherically symmetric, the planet's bulge is axisymmetric with an axis that coincides with the rotation axis. Another way to say this is that there are gravitational multipole moments, but they are aligned with the axis, so it are time invariant as the planet rotates. Now I'm perfectly sure AN knows this, but the way his post was phrased certainly SEEMED to say that simply by having an equatorial bulge, a spinning planet would radiate.

The whole discussion then gets further and further away from the original dispute. shalayka talks about isolated rotating sources in response to AN's discussion of them, while AN starts talking about back reaction, so they have essentially swapped topics, adding to the confusion. During this discussion, shalayka mentioned the Kerr metric for a rotating body as part of a discussion on why axisymmetric rotating bodies would not radiate (which is what AN SEEMED to dispute in the previous post). AN then picked on the discrepancy between the spherical Kerr solution and the axisymmetric assumption. Here again AN is simply wrong. The Kerr solution does have a spherical event horizon, but the metric itself is not globally spherically symmetric. For instance, the ergosphere is oblate. Once again, I'm sure AN knows this, but his post reads as if he thinks otherwise.

The whole Kerr solution discussion is misguided, because the Kerr solution is a perfectly reasonable far field approximation for an isolated spinning planet, provided there are no surface irregularities aside from the equatorial bulge. The bulge itself does mean that the field differs slightly from a true Kerr solution, but at great distances, the effect of the bulge will become negligible relative to the contribution of the equivalent spherical mass. Radiation is a different story, and would not become negligible at great distances, unless it was already negligible because of the small size of the quadrupole anisotropy. Therefore the whole discussion reverts to the original point that an axisymmetric rotating body will not radiate.

At this point, can we all agree to the following (please?):

An isolated spherically symmetric system cannot radiate.

A spherically symmetric SUBsystem, which is gravitationally interacting with another body to form a larger system, CAN radiate.

The radiation can either be attributed to quadrupole anisotropy in the larger system or to center of mass acceleration in the smaller system, depending on viewpoint.

An isolated, rotating axisymmetric system cannot radiate.

A rotating axisymmetric SUBsystem can, as above, and for the same reasons as the spherical case.

An isolated rotating NEARLY axisymmetric system CAN radiate provided it has nonvanishing quadrupole moment due to mass distribution within the object.

Planets radiate due to their orbital motions AND due to their rotations (provided they are not perfectly axisymmetric).

I would now like to return to the original point shalayka brought up, namely that the gravitational potential might not be isotropic, because of braking radiation. I disagree with this notion, because it seems to be mixing levels. Since the Einstein field equations predict spherically symmetric gravitational effects from spherically symmetric sources, and ALSO predict the braking radiation, it would seem to be unnecessary to build anisotropy into the basis of the theory. The theory already accounts for the observed anisotropy, simply by embedding the planet into a larger system, containing its sun. The anisotropy then arises from the anisotropy of the larger system, and so it is not necessary to postulate directly that the field equations should be anisotropic.

Since relativity, unlike electromagnetism, is not a linear theory, you can't really consider the sun's field in isolation. If this were electromagnetism, with a positive and negative charge instead of sun and earth, you could calculate the field from the positive charge while the negative charge was absent. Then you could insert the negative charge and find the correct force by applying the preexisting field to it. This works because EM is a linear theory. In GR, in contrast, the response of the planet to the sun's field includes the fact that the presence of the planet alters the total field in a nonlinear way. Therefore, it is the NON-LINEARITY of the field equations that gives the APPEARANCE of anisotropy you have mentioned.

As a final note, just in case everyone is not yet mad at me, let me say that both of you have been behaving rather badly. Please read each other's posts with a little more charity and forbearance, and flamefests like this one will not happen. I have not interacted with shalayka before, so I have no idea what his posting history is. He may be 17 kinds of crank and loon in other threads, for all I know. That is not relevant. If one reads his posts without ASSUMING he is an idiot, then one finds that real communication can take place. Likewise, AN has made enough gaffes in this thread that it is necessary to give him the benefit of the doubt as well. Please do so, and you will find him both knowledgeable and even helpful. On both sides of the discussion, if the other person appears to be saying something droolingly insane, perhaps you should ask for clarification before whipping out the straitjacket.

I have no authority on this site, no claim to the moral high ground, and no desire to slap wrists, but PLEASE! The rest of us on this thread have been treated to a show in which one person, who I know is intelligent and well trained, and another person, who I know nothing against, are whacking blindfolded at each other with bats, while the great pinata of truth lies all undiscovered before them. (Ok, that probably has Newton rolling over in his grave. Apologies to Newton.)

--Stuart Anderson

I don’t like this thread, I’ll tell you why.
First over, Lori Fujita probably does not exist.

If she did, the answers would be like this.

>Well guys, what I’m after here, is to let you know, that through lights travel in space, allot of things happen to it.

What I’m trying to get at here, is that maybe at a distance, light aberates, due to the affect astral bodies place on light as it travels at a distance.

What Einstein brought forwards in his paper on Relativity deals with information before him, as man had to have some proper way of relating to space only.\

There’s none of this. Her answers are cut and dried, socially nonresponsive.This is as in reality she is probably a bunch of sold out process students, who are getting their information directly from a super computer matrix.

They said on the university level, that they were going to do this years ago.

Anytime that you add computer derived data, into a collection of people, its acts as a splinter felon does in the finger and people socially start to argue.

I think that this is what happened in this thread!