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Nongeometric approach to gravity impossible? 
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#55
Mar112, 12:45 AM

P: 381

I'm talking about the Field Theory of Gravitation. Which is about Fields. What you meant above was that the FRW universe is covered by harmonic coordinates and can be modelled as spin2 fields on flat spacetime. Now Field Theory of Gravitation is the formulism for this. Here one must separately model how space expands. In the other thread, someone said Field Theory of Gravitation doesn't have space expansion because this belongs to the curved spacetime formalism. Note the distinctions there are two formalisms involved. We must not mix them. 


#56
Mar112, 12:56 AM

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#57
Mar112, 12:58 AM

P: 381

"I think your logic is wrong in that not all curved spacetime is expanding. The expanding spacetimes of GR are a special class where spatial parts of the metric depend on t. Also field gravity is not the same as GR. They are two different theories, both claim to explain the observed cosmological phenomena but in different ways. In fact I don't think FTG needs expanding space but supposes a fractal distribution of mass. So you can't talk about splicing them together in the way you suggest." 


#58
Mar112, 01:06 AM

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#59
Mar112, 01:08 AM

P: 381




#60
Mar112, 05:02 AM

PF Gold
P: 4,087

But this theory is not as good as GR in explaining observations, and some authorities say it always leads to GR in any case. 


#61
Mar112, 05:18 AM

P: 381

Instead one must use the FTG version which is in the following terms: 


#62
Mar112, 07:49 AM

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P: 8,544

See post #44. 


#63
Mar112, 12:34 PM

P: 381

"The field theory of gravitation is based on the principle of universality of gravitational interaction and has some forms of the principle of equivalence as its particular cases. In FTG there are Minkowski background space and usual concepts of gravity force, gravity field EMT and quanta of gravity field  gravitons. Within FTG there is no infinite force at gravitational radius and compact massive stars could have masses much more than OVlimit. FTG is actually a scalartensor theory and predicts existance of tensor (spin 2) and scalar (spin 0) gravitational waves. Astrophysical tests of FTG will be available in near future. It is quite natural that fundamental description of gravity will be found on quantum level and geometrical description of gravity may be considered as the classical limit of quantum relativistic gravity theory." How does the above differ to Weinberg formulation. They are the same. Hope you can read the paper yourself instead of writing in one line riddles that is so difficult to understand. 


#64
Mar112, 01:31 PM

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P: 8,544

Wald, p383, we may view the full Einstein equation (γ_{ab} not assumed to be "small") as the sum of this free piece, plus a nonlinear selfinteracting term, ie. we may view Einstein's equation as an equation for a selfinteracting spin2 field ... 


#65
Mar112, 05:15 PM

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#66
Mar112, 05:24 PM

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#67
Mar112, 05:29 PM

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#68
Mar112, 06:03 PM

PF Gold
P: 4,087

Can you point me to some elit that shows the MTW treatment ?



#69
Mar112, 06:18 PM

P: 381

find this starting line: "5. Einstein's geometrodynamics viewed as the standard field theory for a field of spin 2 in an "unobservable flat spacetime" background...". Please share how it differs to your description of Baryshev's as when you described it in the other thread: "FTG is a classical field theory that begins with the Lagrangian which has three terms, one each for the field, one for the matter and crucially one for the interaction between the field and the matter. The exchange boson, if the theory was quantized would be spin2. All this is done in Minkowski spacetime." atyy.. since you are familiar with the MTW approach, please share how it differs to the above FTG theme. Thanks. 


#70
Mar112, 06:40 PM

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See, for example: http://arxiv.org/abs/0809.2328 Almost all other authors on spin 2 field theory would disagree with every prediction of the above paper, believing that spin 2 field theory would agree with GR instead. As with atyy, I am not in a position to judge Baryshev on the merits. One comment on the disagreement is noted in the following: http://arxiv.org/abs/1106.2476 : "Finally, let us mention that approaches exist that treat gravity as simply a spin2 field on flat space [114, 115]. It has been conjectured that one could reconstruct the EinsteinHilbert action in such an approach by considering consisitency conditions order by order in perturbation theory. This will, of course, be an invalid treatment when gravity is strong, and in cosmology." Most authors disagree with this paragraph and argue that such recovery of the EinsteinHilbert action is imperative, and that the comment on invalidity is itself invalid. 


#71
Mar112, 06:55 PM

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P: 1,685

There is a sublety regarding scaling when you go from the linear to the full nonlinear theory around certain solutions. So when doing perturbation theory around say the Schwarschild solution you naively run into an inconsistency and that is what Baryshev is picking up on.
What he fails to mention is that this problem was dealt with long ago by Vanshtein. "To the problem of nonvanishing gravitation mass”, Phys. Lett. B, 39, 393–394, (1972) But anyway, this is way beyond the scope of this thread and is just arguably going to confuse things more than they already are. 


#72
Mar112, 07:07 PM

P: 381




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