This is not a Q, but it's related to several threads here -- feel free to move if you don't think it belongs.
In my sparring about Mach and GR, I ran across a commentary by B. Mashhoon and another about Mach. Masshoon has a number of papers on gravitomagnetism, relativistic rotation, etc stuff, and I was sort of smoking them over. Interesting stuff, at least for me. Anyway, this one caught my eye:
This is about GEM and what Mashhoon calls "critical speed", which is c/sqrt(3). Sound familiar? That is the speed above which an object "thrown down" radially from infinity in Schwarzchild will appear to *slow down*, rather than accelerate (it's coordinate speed as measured by the far away Schwarzschild observer, of course). You may recall a number of threads about this, one prompted by that Felber/Farber/Whatever guy who made such a big deal about it.
Well, Mashhoon discusses that in GEM context. There's a nice quick derivation of the GEM equations, and you'll note how the factor of 2/4 comes out. Mashhoon like to split the factor of 4 up, letting one go with the B_g field and the other go in the force equation:
F = mg + 2mv x B
He also prefers Gaussian-style units (like most EM high priests), so he has a v/c there, rather than plain v.
Anyway, Mashhoon thinks this "critical speed" may play an important role in what is *obversed* with relativistic flows of matter. Read on.