Aether for quantum gravity?! Dittrich says yes!

On the aether approach, we add the clocks to the system, by way of

– Gaussian reference fluids

– (honest) aether)

– dust proposals.

Huggett: Does the aether introduce some parameter? Dittrich: Aether is a bit more subtle, aether is just a vector field that is hypersurface-orthogonal and provides a slicing of the manifold.

Sudarski: does this break Lorentz-invariance? Dittrich seems willing to bite the bullett, although she describes this as a “diffeomorphism-invariant way” to break Lorentz invariance. This blogger, for one, is puzzled!

Live blogging: Dittric

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Dittrich discusses the “naive” solution of relational observables.

Spatial positions together with time co-ordinates are observables, as in:

“Position of particle at 5pm” is an observable.

But this is problematic:

a) In QG we do pre- or postdictions, seemingly incompatible

b) What are good clocks?

live blogging: Sudarsky

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Discussion.

Audience:  Can you say a bit more about fine-tuning?

Daniel:  The technique has been applied to a very simple model.  We haven’t yet considered more complex models.

Audience:  Question about the Bunch-Davies vacuum.  Can you use other vacuum states?

Daniel:  Yes, but that doesn’t change the fundamental question:  How do you break the initial symmetry?

live blogging: Sudarsky

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The quantity of interest (that is zero without CSL, but non-zero with CSL) is a result of a random walk on the complex plane…  One can now calculate this quantity and compare it with the CMB data, and this, it turns out, let’s us calculate CSL predictions (like the collapse rate parameter).