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Nongeometric approach to gravity impossible? 
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#73
Mar112, 07:31 PM

P: 381

Also in the MTW approach where space can expand (according to atyy). Take note of this logic: Since expanding space is automatically curved spacetime, and since curved spacetime is just spin2 field on flat spacetime. Then expanding space is composed of spin2 field and flat spacetime. Therefore expanding space is related to expanding space&spin2 field and expanding space&flat spacetime. How does one imagine or model expanding space&spin2 field for example? Or expanding space&flat spacetime which is a Milne model that isn't valid. Can one say that when one adds spin2 to Milne model. It becomes valid? Do you see if there is something wrong with my analysis. Thanks. 


#74
Mar112, 07:56 PM

PF Gold
P: 4,087

For me, the eyeopener is that the nonlinearity of GR emerges from the coupling of the boson field to the whole Lagrangian, requiring the infinite series. I think it also shows the deficiency in the FTG approach which has been highlighted in other posts. 


#75
Mar112, 08:04 PM

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PF Gold
P: 5,027

This was posted in another thread, but here is a recent defense by Deser of the derivation of GR from spin 2 field:
http://arxiv.org/abs/0910.2975 


#76
Mar112, 08:09 PM

P: 381

Spin2 field over flat spacetime produces an illusion of curved spacetime. Now when space expand. Why did it use the curved spacetime thing when it is just an illusion. Shouldn't it interact with the more primary flat spacetime as it's the more original? 


#77
Mar112, 08:29 PM

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#78
Mar112, 08:37 PM

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#79
Mar112, 08:48 PM

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http://www.einsteinonline.info/spotlights/big_bangs "The term "big bang" has two slightly different meanings, and the answer to questions like "Did the big bang really happen" depends crucially on which of the two big bangs you are talking about." 


#80
Mar112, 09:17 PM

P: 381

Intermission: About milne expansion... In between supergalatic clusters are empty space devoid of any matter and spin2 fields (let's say we can ignore the CMB and cosmic rays), then the region of the space can be considered flat. Then can't it be considered a milne expansion? 


#81
Mar112, 09:26 PM

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#82
Mar112, 09:35 PM

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#83
Mar112, 09:42 PM

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#84
Mar112, 09:47 PM

P: 381

classical spin 2 theory? quantum spin 2 theory? I thought all spin 2 theory are quantum. But then you can't have spin 2 particles in classical theory just like you can't have photons in classical electrodynamics. 


#85
Mar112, 10:18 PM

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#86
Mar112, 10:23 PM

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#87
Mar112, 10:42 PM

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Analogously for gravity. 


#88
Mar112, 11:32 PM

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#89
Mar212, 02:26 AM

P: 381

Can one consider FRW spacetime = Milne Spacetime + Spin2 fields?? Why not? It's analogous to curved spacetime = flat spacetime + spin2 fields? 


#90
Mar212, 06:52 AM

P: 381

Now do you treat this "curved spacetime = flat spacetime + spin2 field" thing as some kind of Correspondence or Duality like the Asd/CFT Correspondense? Here the FRW Universe is treated as curved spacetime and never as flat spacetime + spin2 field because this is not actual but only a dual just like the AsD/CFT Correspondense where the boundary thing of some distance area is just dual and can't be taken as actual? Please elaborate what is your thinking or let others assist here because over days I'm so frustrated already why my simple question of how the FRW Space can't be treated as an actual flat spacetime + spin2 field is not answered. When I asked you this, you always replied continuously to use curved spacetime which was not what I was asking.. unless you treat this whole curved spacetime=flat spacetime + spin2 field as just correspondense and the latter not an actual replacement for the former? Hope you can answer clearly now or please others assist here. Thanks. 


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