@PC Paul -- Re: Duh?
Hum, I didn't see that grammatical (nor the redundant 'the') even after a second reading, amazing! It irks me there's no post posting edit feature to correct it.
Well, I'm not in disagreement with your points, but more on that in a moment. The trouble with forums is that précising, sweeping statements and over-generalisations are the order of the day. Some weeks back I made a quite detailed post to which there seemed to be little disagreement (all thumbs up) but the immediate following post was, quoting verbatim:
"Summarize man. Summarize."
To which there were 5 thumbs up and one down (and that wasn't me). One's damned either way.
In my defence, I made the point about Voyager and the 'edge' of solar system because it's current and topical, it was not intended to be precise physics. Even if the solar system has a very sharp edge on a solar scale, it's still going to span a long way in human terms—a damn side larger than a few metres I'd suggest. In one sense that was the point I was making, but also I was suggesting that such extraordinary precision wasn't feasible, certainly not in any practical sense. You'll also note that I did put 'edge' in quotes because the concept was, for all practical considerations, hypothetical.
You'll also note that I was affronted by the extraordinary and unqualified statement from which I quoted, this I amplified upon in my reply to asdf.
Back to your point about the centre of mass of the solar system and the centre of rotation. In principle, I'd have to agree with this, but I come back to why I initially made the post which is the incredible ramifications of determining the centre of mass of the solar system to within a metre or so. Frankly, Dr Hobbs shouldn't be allowed to make such a sweeping statement without substantial qualification. Such an extraordinary statement requires an extraordinary explanation.
In essence, Dr Hobbs statement brings more the engineer out in me than scientist. Not only is there the practical problem of measurement, which is well outside the scope and precision of any human endeavour to date, but also at such huge precision the question of whether our current understanding of the laws of physics is sufficient to make a reasonable / sensible calculation of such precision. (That's assuming we could actually measure the centre of mass to within an 'accuracy' of a metre.)
Whilst we may think we've measured the centre of mass with such accuracy it may not be the case as our mathematical analogue of nature may be sufficiently imprecise as to make the measurement essentially useless. For starters, at extreme precision over many magnitudes, actual relativity in nature may not behave exactly as the mathematical analogue predicts, simply: relativity may be non-linear at the extremities. (This matter is still open to experimentation and debate, as with all aspects of relativity.)
Remember, physics is accursed with that damn mathematical concept called zero, it mucks up the Big Bang, Black holes, and quantum equations. In fact, New Scientist, last week (17 August '13, No. 2930) had an article on the divide-by-zero problem titled 'The infinity illusion', p32:
http://www.newscientist.com/article/mg21929300.700-infinitys-end-time-to-ditch-the-neverending-story.html
However, for the moment let's assume relativity is precisely as the equations show it to be, then we're back again to the problem of measurement. As I see it, we've serious problems in determining an instantaneous result for the centre of mass, as the solar system is a big place and relativistic effects would matter at such precision—determining the integrand so to speak would seem very problematic. Moreover, calculating the centre of mass to such precision over time would also be problematic as the solar system is full of dynamic components, thus the centre would wobble and appear fuzzy. This, in turn, would be exacerbated by the fact that the solar system itself is being acted upon by our galaxy's components as it travels through space.
I don't claim to know the extent of these effects but I'll need a damn good argument to convince me that 'within a metre or so' has any practical meaning outside the hypothetical.