Talk:Einstein force
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This is a first stab... perhaps someone who knows this well could take a glance? Since I just learned this term half an hour ago, I'm probably not very qualified. ^_^ But since there's no online definition I could find, I went ahead and made this page. --Starwed 19:55, 21 September 2005 (UTC)
- Hi, Starwed (thanks for creating a proper user account!), where exactly did you encounter this term? A textbook citation would be nice. I have not seen it used myself, speaking as one fairly familiar with the literature on gtr. One problem I noticed is that you mention time, but didn't clarify if you mean proper time. If I could see the book/paper where you saw this used in context, I think it will turn out that you garbled a reference to the acceleration vector (covariant derivative of a timelike unit vector field). See congruence (general relativity) and references therein.
- How do you expect this article to fit in with the other articles on relativistic physics? As far as I can see it serves no useful purpose, especially because of the articles on congruences and related topics.---CH (talk) 15:54, 2 October 2005 (UTC)
Hello, I encountered this term in a class on classical analytic mechanics. The only specific reference I can cite is a book by Cornelius Lanczos called The Variational Principles of Mechanics (p50, I think, although I don't have a copy handy.) While Lanczos worked in the field of GR, the context of the book is normal (nonrelativistic) mechanics. To work in a noninertial reference frame, it's necessary to introduce several apparent (or fictitious) forces resulting from the accelerated motion of the frame relative to some inertial frame. The force which results from translational motion he labeled the Einstein force. (He also treats three other forces arising from rotation of the frame: the Coriolis force, the centrifugal force, and a third force which only arises when the angular velocity vector changes in time.)
Searching online, I can't really find any references to the Einstein force, so it may well be that this is not the preferred name, and that this article should redirect to another one. I have come across the term in at least one other source, again dealing with analytic mechanics. Naturally I now can't find the bloody article/webpage I saw it in. ^_^ I certainly have no complaints about simply renaming/redirecting this page, but if there's a standard name for this "force" I don't know it.--Starwed 05:53, 13 October 2005 (UTC)
Also, I noticed that the article on Fictitious forces does discuss this force, but doesn't give it a name.--Starwed 21:44, 13 October 2005 (UTC)
- Wow, sorry I didn't see this comment last year, Starwed!
- I've read Lanczos's book, and don't recall seeing this term, but I'll take your word for it. Yes, Lanczos did some good stuff, but he is of a generation which just predates the "moderns" explempified by Misner, Thorne and Wheeler and subsequent authors of standard textbooks since about 1973. See Golden Age of General Relativity. I lack energy to go into much detail here but the fictitious force thing is vastly overstated in some WP articles.
- A modern approach would identify gravitation with curvature tensor. In particular, via the Jacobi geodesic deviation formula, the tidal tensor or electrogravitic tensor is part of the Riemann curvature tensor, and tidal forces are certainly not fictitious. Neither are spin-spin forces. That is, a spinning test particle or gryoscope orbiting a Kerr hole actually is forced off course [a geodesic path] by tiny spin-spin forces! Although this is not mentioned in many textbooks you can find it in MTW if you look hard. These spin-spin forces are encoded by the other half of the Weyl tensor (agrees with Riemann tensor in vacuum regions), the magnetogravitic tensor. (The electrogravitic tensor and magnetogravitic tensors are only defined with respect to some observer, just like the electric and magnetic fields, the two parts of the EM field tensor.)
- So my objections stand.---CH 07:42, 17 June 2006 (UTC)
