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marcus
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#123
Mar9-12, 08:21 PM
Astronomy
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PF Gold
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Hi Paulibus, beyond what I said in post #121 by way of reply
I want to emphasize the testabiliity angle which is one of the possibilities that makes this proposal exciting:
==quote page 4, http://arxiv.org/pdf/1203.1040v1.pdf ==
As we have seen, any solution to GR, with arbitrary cosmological constant, is a solution to our theory. However, it is clear that the reverse is not true. Our theory is expected to permit solutions that are not present in GR. This opens up the possibility of finding some interesting and potentially testable new features. Work is under way to study the impact of these new features, beginning with cosmological solutions of the specific model presented here.
==endquote==

Also to reiterate the main result for clarity
==quote page 2==
Actually, we can go even further. Any solution of GR, vacuum or otherwise, is also a solution to our theory, whatever the value of the vacuum curvature. As the vacuum energy drops out of the dynamics, we are free to choose the vacuum curvature with a clean conscience. Indeed, one can straightforwardly check that the field equations are satisfied by the choice,
G ̃ab = −Λ ̃g ̃ab + τab, T ̃ab = −σg ̃ab + τab ( 9 )
where τab describes the matter excitations above the vacuum, σ is the vacuum energy, and Λ ̃ is the vacuum curvature.

This follows from the fact that the equations of motion are linear in E ̃ab, with constant contributions dropping out completely. In particular, this means that the standard ΛCDM cosmology, with Λ chosen empirically without any concern, is a perfectly good solution to our theory, and does not suffer from the same fine tuning issues as the corresponding solution in GR.
==endquote==

Assuming this initiative goes thru, the ball is now in the relativist's court. It is they who must explain the value of the constant vacuum curvature, if it needs explaining.

Does it need any more explanation than, for example, the value of Newton G?
Perhaps, perhaps not. We'll see.