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Originally Posted by Nereid
A couple of other folk have provided good inputs on this topic, including the observation that extremely accurate spacecraft navagation throughout the solar system has been possible without needing to use the 'MUCH stronger influence' of electricity and magnetism. These navigation successes include, of course, observation; they are also, in a sense, better than observation!
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Yes, and I agree that "relative" to earth, these measurements of gravity between the various bodies in the solar system sure seem to work with great precision. I've been poking around through the methods of calculation however, and I see only 2D "measurements" of the sun's density. In other words, I see mention of the earths orbit of rotation around the sun, but no mention of the sun's 22 year rotation cycle of it's magnetic pole with its spin axis. If the sun and our whole solar system is rotating around once ever 22 years as I believe is the case, this movement in 3d (rather than 2d) should be factored into the density measurements of the sun in some way. I don't see anything even remotely like that happening in these measurements. That extra centrifical force from a 3rd dimension is not factored into any of these calculations as far as I can tell, and while it may not affect RELATIVE gravity to exclude this 3rd dimension of movement, it will certainly affect any density measurements.
That is the line of thinking I'm persuing at the moment. I'll let you know when I've got something to share. It think however you must admit that the sun's 22 year rotation cycle is not factored into these density measurements and that "could" be a significant issue as it relates to density, even if it does not affect relative gravity measurements.
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The nature of electrical and magnetic 'influence' - in terms of affecting the motions of bodies in the solar system (ranging in mass from dust to the Sun) - has been well studied, and such influences well characterised (i.e. the "physics" is well understood).
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I must agree. That's why I've found this problem to be so perplexing and why I think it's important to resolve this issue logically and scientifically. I'm still working on it. Nobody abandoned the gas model the first time one meausement didn't seem to jive with the model. That caution should be applied here as well. Until we understand how the rotation of solar system itself factors into these measurements, I think it is VERY premature to get too carried away over a single measurement. I have great confidence that this issue can and will be resolved logically. At the moment I suspect it will involve the sun's 22 year rotation cycle. It seems to me that this movement is very important as it relates to the question of density, even though in relative terms it may have little affect on gravity measurements.
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Look at this another way - the motions of solar system objects* are exactly accounted for (i.e. within the error bars) with the application of only gravity (indeed, you don't even need General Relativity for much other than Mercury's orbit)
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Sure, but all these measurements are 2D measurements as far as I can tell. In other words they "assume' that there is no movement vertically. Every measurement is based on a "relative" orbit around a FIXED (non moving) star. Since we have some evidence the sun is rotating around a universal field, this rotation cycle SHOULD be factored into density meausurements since it will certainly affect these meausrements, even if it is not relevant to relative gravity.
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and, in the case of very small objects, some subtle effects due to photons (I see - from your posts earlier today - that you are unfamiliar with several well-understood properties of photons; this may be another new one for you ... photons have no mass but have non-zero momentum). In all this, no assumptions about the composition of the bodies are made.
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I simply fail to see the point of using a particle that presumably has NO mass to measure a gravity well. What is more difficult to understand is how folks think a massless particle is lensed, but somehow we can ignore the affect of this lensing on neutrinos. That is illogical IMO. It the curvature applies to presumably massless particles, then it must also apply to particles with mass. You can't make one argument and ignore the other.
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Finally, just to note that these solar system objects include Mercury (which may well be composed of mostly Fe/Ni), Io (which has a huge current flowing between itself and Jupiter, and is moving through a radation belt that would make Chernobyl look starved), and the Earth (which has a magnetic field, lots of iron, currents, ...).
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I'm starting to think that these currents are responsible for holding things together, not pushing them apart. In other words, I suspect when we factor in a 3rd dimension of rotation, we'll end up with the opposite problem of trying to explain what holds it all together. I've got a lot of work to do however before I can really comment any further.