Decoherent histories analysis of models without time

Halliwell, J. J.

doi:10.1590/s0103-97332005000200015

Cited by 2 publications

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References 23 publications

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“…In addition, for the present situation, it makes sense to further restrict the 4geometries we consider to those that look essentially like our present universe (roughly a spatially flat Robertson-Walker universe), except with vorticity. Further, there are ‡ also called decoherent histories [41,42,43,44,45,46,47,48] or consistent histories [49,50,51,52] estimates for how we would expect vorticity to vary with time if there were any vorticity. Vorticity might not be homogeneous, however.…”

Section: Overviewmentioning

confidence: 99%

The rotation problem

Jones

2017

Preprint

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On a large scale, inertial frames seem not to rotate relative to the average matter distribution in the universe. Without absolute space or finely tuned initial conditions, it is difficult to explain the lack of relative rotation. Two classical (nonquantum) arguments have been proposed to explain why: (1) that gravitational fields (including inertial fields) be completely determined by the matter distribution, with no independent degrees of freedom for the gravitational field (AKA Mach's principle).(2) inflation. Although either of these is a possible explanation, a more likely explanation comes from considering reasonable forms of quantum gravity. A semiclassical approximation to quantum gravity shows that phase interference would cancel out cosmologies with significant relative rotation. A generic general estimate for a perfect fluid cosmology with a realistic variation of average vorticity with cosmological scale factor shows that only cosmologies with an average present relative rotation smaller than about L * H 2 ≈ 10 −71 radians per year could contribute significantly to a measurement of relative rotation rate, where L * is the Planck length and H is the present value of the Hubble parameter.

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