As a reminder of the main topic here, this quote from Bianchi and Rovelli's piece in Nature
sums up what the thread is about
==quote B&R's piece in Nature July 15, 2010==
But it is a conceptual mistake to confuse Λ with QFT’s vacuum energy. Λ cannot be reduced to the ill-understood effect of QFT’s vacuum energy — or that of any other mysterious substance
. Λ is a sort of ‘zero-point curvature
’; it is a repulsive force caused by the intrinsic dynamics of space-time.
Tests on the ΛCDM model must continue and alternative ideas must be explored. But it is our opinion — and that of many relativists — that saying dark energy is a ‘great mystery’, for a force explained by current theory, is misleading. It is especially wrong to talk about a ‘substance’. It is like attributing the force that pushes us out of a turning merry-go-round to a ‘mysterious substance’.
More back a few posts in post #97 http://physicsforums.com/showthread....52#post3626952
Sorry to say I do not have a working link to the B&R piece in Nature. If you have a subscription, it's
Cosmology forum: Is dark energy really a mystery?
Eugenio Bianchi, Carlo Rovelli, and Rocky Kolb
Nature 466, 321–322 (15 July 2010)
However they make the same arguments at greater length and in more detail in this article:
Google "bianchi prejudices constant" and get http://arxiv.org/abs/1002.3966
The new element, which I first learned of yesterday, and which is discussed in the previous two posts #111 and #112, is
this paper by two physicists in the particle theory group at Nottingham (Nottinghamsters?
Cleaning up the cosmological constant
Ian Kimpton, Antonio Padilla
(Submitted on 5 Mar 2012)
We present a novel idea for screening the vacuum energy contribution to the overall value of the cosmological constant, thereby enabling us to choose the bare value of the vacuum curvature empirically, without any need to worry about the zero-point energy contributions of each particle. The trick is to couple matter to a metric that is really a composite of other fields, with the property that the square-root of its determinant is the integrand of a topological invariant, and/or a total derivative. This ensures that the vacuum energy contribution to the Lagrangian is non-dynamical. We then give an explicit example of a theory with this property that is free from Ostrogradski ghosts, and is consistent with solar system physics and cosmological tests.
Padilla's paper depends on prior work http://arxiv.org/abs/1106.2000
by Copeland et al. Copeland is also at Nottingham. This was published earlier this year in Physical Review Letters.