Your project may be ill-advised
Hi, Michel,
I appreciate that you are trying to describe what you have in mind, but I still can only guess what you want to do even in broad outline. It certainly isn't making things any easier that (as I guess), English is not your first language, but I am trying to take this into account!
I have the impression that you might be trying to say that you wish to review in great detail, regarding the observed motion of the inner planets and the observed motion of certain spacecraft , the entire process of
1. formulating a theory of gravitation,
2. forming a model in said theory of N-body motion in a planetary system,
(3a. designing methods of tracking planetary motion from Earth),
(3b. designing a spacecraft mission to study the alleged Pioneer effect),
4. taking observations,
5. analyzing the data.
Please don't take this the wrong way, but it worries me that I keep noticiing indications in your posts (and this is independent of the possible language barrier) that you have little idea of how the above process works, and that you are
vastly underestimating the complexity of this process or the kinds of things which can go wrong.
Let me try again: people go to school to become astronomers, and this requires not only long years of classroom study, but more to the point, intense individual tuition with hands-on experience in the lab. And while many hear the call, few are eventually chosen, in part because this is such a demanding field. In my view the demands placed upon observational astronomers is particularly enormous, in terms of the sheer amount of stuff they need to master. In contrast, on the theoretical end, I consider mastering gtr (and related ideas like PPN) to be by far the
least challenging task faced by an untrained amateur hoping to understand in detail the scientific issues involved here. BTW, few observational astronomers are masters of gtr; they mostly rely on their theoretical colleagues to handle the theoretical side. There is good reason for this: they are responsible for the really hard stuff, so it makes sense to delegate responsibility, as it were, wherever possible.
In short, you need to be a master of
ordinary science (which requires not only training but extensive experience as a working scientist) before you can hope to follow the twists and turns of
extraordinary science!
Let me try yet again: anyone truly wishing to understand all the issues would need to be among other things like a mechanic with enough knowledge to take apart a four-engine jetliner and put it back together again. Ditto, for an airport radar system. Ditto, for a million line FORTRAN program. That is just in terms of having practical experience with some of the "ordinary physics" which might explain the alleged effect, as well as with the data analysis issue.
Some specific points:
lalbatros said:
My idea is to have an hands-on approach on a few questions in GR (as a hobby)
Well, I know that it is quite possible to learn gtr from books, as a hobby, since I did just that. But I had the benefit of extensive formal training in math, which was invaluable--- I doubt I could have picked up much gtr if I had been attempting to simultaneously pick up all the mathematical background, entirely on my own. One reason for this is that all the textbooks assume students share some common background, and while it would be difficult (and incredibly tedious) to try to explain this in detail, I am confident that most who have that background and who think about how they and their colleagues learn new material will be very much aware of how necessary it is that one be prepared to understand what one reads in textbooks, by having formal training up to the starting point of the textbook in question.
By the same token, I happen to have a bit of laboratory experience in astronomy, so I have at least some appreciation of how many skills are needed to design experiments, take measurements, and analyze the data. There is a good deal of flying by instinct which takes judgement and experience; these are things which simply cannot be taught in any book. You have to learn them on-the-job in a lab, I think.
lalbatros said:
You failed to respond to my challenge to describe this alleged "question". This might be a mere problem of French(?) to English; maybe you meant "precession of perihelia phenomena"? But in any case, I have the sense you think there is room to doubt that Einstein's formula gives good results (or that more accurate formulas, typically derived in the context of gtr or the wider context of PPN formalism, give even better results); there is not!
lalbatros said:
myself with the numbers, not in a book
This seems to suggest you expect to see the experimenter's notebooks, as it were, but I put it to you that without extensive laboratory experience, one has no chance whatever of understanding such a notebook. Similar comments for computer programs used in tracking spacecraft , for analyzing the data, and so on.
lalbatros said:
the pionner 10/11 question
Here at least we all agree that there is an open problem: is the alleged Pioneer effect real, and if so, how does it manifest itself and what is its simplest explanation? (Roughly speaking.)
lalbatros said:
The second point may be more difficult because it involves orbits and a complicated analysis of the Doppler data.
OK, about those orbits: did you notice that I have alluded on several recent occasions to the fact that the mathematical models used in the literature for tracking spacecraft are quite awkward hybrids of Newtonian and relativistic physics? There is actually a good reason for that, and it reinforces my point: this stuff is so complicated and has been built up in such tiny increments of trial and error that it would not be easy for NASA to adopt fully relativistic methods. Yet, the hybrid is being strained, perhaps to the breaking point, and there has been increasing interest in recent years (motivated by wider issues that resolving the alleged Pioneer effect, to be sure) in exploring fully relativistic navigation systems, among other things for purposes of spacecraft tracking and navigation in Solar system missions. But these proposals are sufficiently revolutionary that everyone agrees that NASA/ESA would need to put in huge effort and eventually test the waters with some kind of spacecraft mission intended primarily to test a rudimentary Coll navigation system (or some variant). I suggested that with sufficient cleverness (and astronomers are very clever indeed at getting maximal bang from the taxypayers buck), perhaps such a mission could double as a mission studying the alleged Pioneer effect in a "cleaner" manner.
lalbatros said:
I would also like to compare the approximated ppn force formula
What is this "PPN force formula"?
lalbatros said:
What exact solution would that be? To what equations? In what theory?
Do you mean: some kind of "exact solution" describing test particle motion in some spacetime model? Or some kind of "exact solution" describing the geometry of a spacetime model, allowing for some kind of hypothetical new physics?
lalbatros said:
And I don't know how these topics will compete with my regular job!
Well, this is the thing. Why do you think you have the knowledge and expertise to study these issues? I am guessing that you think that only because you lack my level of astrometry-related knowledge and experience, which is certainly not enough to enable me to study many of the issues involved myself, but is enough for me to have some idea of why I lack enough knowledge and experience to be able to study very many of them! IOW, I know (or have some idea of)
how much I do not know. And I have some appreciation of this: for which issues I might be able to acquire sufficient background to understand sufficiently well to follow the developing saga in some depth, and which issues I will have to leave to others who have the above-mentioned practical experience as working astronomers.
Which brings me to another point which I should stress in case it is not already obvious from what I said above: figuring out what is going on in the alleged "Pioneer effect" (if it indeed exists) will be a communal effort, because no one scientist has anything even approaching mastery of all the stuff which is involved in excluding possible sources of error, critiquing suggested theoretical models, and so on.
Again, please don't take this the wrong way! The bottom line is that science is really, really hard. Cutting edge science is the hardest of all. Scientists aren't trying to exclude anyone from sitting at the table, it is just that these issues are so extensive, manifold, subtle, and challenging that it takes not only long years of "book learning" but extensive on-the-job experience to appreciate most of them.
