Why all these prejudices against a constant? ( dark energy is a fake probem)

[marcus]

Here's the link to Padilla's article again:

http://arxiv.org/abs/1203.1040
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.
4 pages

==a key quote==
In summary, then, we have proposed a novel way to clean up the cosmological constant problem. By coupling matter to a composite metric, g ̃ab(φ, ∂φ, . . .), satisfying the property (1),
we have been able to eliminate the troublesome vacuum energy from contributing to the dynamics of the system. Thus one ought to be able to choose the vacuum curvature to take on an empirical value, as dictated by observation, with a clean conscience. This is the take home message of this paper.
==endquote==

===============EDIT TO REPLY TO NEXT POST================
Hi Paulibus, since I can still edit I'll reply here. I simply agree. It makes sense to me too. So much for "dark energy". I doubt we're ever going to be able to use it to run the family car or grind the corn to make the tortillas! But I wanted to say that I relished your reference to that perceptive French expression for non-Baconian speculations (la haute poppicocquerie) and was glad to hear about Helge Kragh's book
"Higher Speculations -- Grand Theories and Failed revolutions in Physics and Cosmology" O.U.P, 2011.

 

[Paulibus]

What ( Kimpton and Padilla) are talking about ...is a mathematical
technique to "degravitate" the QFT vacuum energy ...

Because the Equivalence Principle rules GR, would this mean that the same mathematical
technique would also “deinertialise ” the QFT vacuum energy? Seems reasonable to me. I can’t see how either the gravitational or inertial mass of the entire universe’s vacuum energy could be detected and measured; spring balances and accelerating rockets are useful only for relatively local stuff.

 

[marcus]

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 + τ_ab, T ̃_ab = −σg ̃_ab + τ_ab ( 9 )
where τ_ab 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.

 

[marcus]

Why all these prejudices against a constant? ("dark energy" is a fake probem)

Posts about "exotic matter and the Casimir engine" and "exotic matter and the Casimir effect" wouldn't really belong in this thread.

What's being discussed in the thread is the widely (but not universally!) shared view that the observed expansion speedup is best explained as simply due to a constant Λ which occurs naturally (along with Newton G) in the Einstein equation.

These two constants G and Λ are those allowed by the symmetry of the theory and so *must* appear in the equation. Either or both could, of course, have turned out to be zero, but in fact neither did: both are positive.
This is the (classical) equation which to the best of our knowledge governs the evolution of geometry.

So it's inappropriate to talk about "dark energy" or "zero point energy" in this context, any more than one would drag in such stuff in connection with Newton G.
There need be no mention of "exotic matter" fields to explain the value of Λ any more than one needs such inventions to explain the value of G.
Seen from this perspective, since today's quantum field theory is based on a rigid flat geometry in which dynamic expanding geometry necessarily cannot be captured, it can have little or no relevance to explaining Λ: whatever oversized value of "vacuum energy" QFT theoreticians might come up with has no bearing on the observed value of the cosmological constant. They just need to go back and get their flatspace vacuum energy right.
For an interesting recent contribution to this discussion see Kimpton Padilla's paper.

http://arxiv.org/abs/1203.1040
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.
4 pages