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Sciama's Machian Origin of Inertia 
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#1
Feb112, 10:32 PM

P: 373

Hi,
I'm interested in what people think of Dennis Sciama's 1953 paper on the origin of inertia in which he shows how Mach's principle could work using a simple argument with Maxwelltype gravitational field equations: http://articles.adsabs.harvard.edu/c...;filetype=.pdf John 


#2
Feb212, 08:43 AM

P: 5,632

I think the basis for his assumptions is 'beyond my paygrade'..
but his 'advisors' are sure not 'hacks' you might find this discussion of interest: http://en.wikipedia.org/wiki/Mach%27s_principle so it's not like Einstein ignored Mach. 


#3
Feb212, 03:31 PM

P: 156

the philosophical argument that Einstein sort of understood from this (If I remember correctly) was that the local physical laws in a part of the universe may well be related to the inertial mass present, for it is clear that the fabric of spacetime is fully controlled by it. investigations for this principle is very much out of reach by any means, for us. One can imagine though...



#4
Feb212, 03:42 PM

Sci Advisor
P: 2,670

Sciama's Machian Origin of Inertia
I haven't read the paper (don't have time to rigorously read through it, and I won't understand it unless I am fairly rigorous I think), but I can give a few "general considerations".
1) The main problem regarding Mach's principle is its definition. There are as many definitions of Mach's principle as you can shake a stick at, ranging from mathematically precise statements which we can test (e.g. Brans Dicke theory's omega parameter), to pretty vague and "unfalsifiable". 2) Einstein explicitly tried to "incorporate" Mach's principle into his theory. But I believe he merely took it in the context "matter tells space how to bend", "space tells matter how to move". In this context, certainly "Mach's principle" is obeyed. When the LenseThirring effect was first established, Einstein thought that this was a wonderful confirmation of Mach's principle. A spherical shell of mass, (e.g. the universe around us) which is rotating, will determine the standard of rest (or inertial frames) inside it, and thus the angular momentum vectors will tend to rotate along with the rotation of the spherical shell (also called frame dragging). This effect is entirely native in GR. 


#5
Feb212, 04:31 PM

Emeritus
Sci Advisor
P: 7,596

From a quick read, it appears to require an additional field, which Sciama calls a potential, which is specifically a rank 2 tensor.
The problem in general is finding any experimental justification for the existence of these extra forces, or potentials. I'd expect Sciama's theory to fit into testing via the PPN formalism http://en.wikipedia.org/w/index.php?...ldid=441595158 but I don't see any listing for it the alternate theories of gravitation section of the wiki, http://en.wikipedia.org/w/index.php?...ldid=472874071, which lists the PPN parameters predictions for a variety of theories. I"m not sure if this is because my assumption it should have PPN parameters is incorrect, or whether it's just not included. 


#6
Feb212, 05:11 PM

Sci Advisor
PF Gold
P: 5,027

At this point, I don't have time to comment on the substance of this idea, but merely add some references:
1) by Wolgang Rindler: http://books.google.com/books?id=fKg...nciple&f=false 2) http://arxiv.org/abs/physics/0609026 3) http://arxiv.org/abs/0708.3518 4) Finally, not closely related to Sciama's ideas, I note the best modern advocate of Machian ideas is Julian Barbour, and the following includes his demonstration that one formulation of Mach's principle is included in GR: http://arxiv.org/abs/1007.3368 


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