REVIEW 4 cited by
Cosmological ensemble and directional averages of observables
Not yet reviewed by Pith; the record is open.
This paper has not been read by Pith yet. Machine review is queued; the pith claim, tier, and objections will appear here once it completes.
SPECIMEN: schema-true, not a live event
T0 review · schema-true
One-sentence machine reading of the paper's core claim.
pith:XXXXXXXX · record.json · timestamp
Signed reviews
read the original abstract
We show that at second order, ensemble averages of observables and directional averages do not commute due to gravitational lensing -- observing the same thing in many directions over the sky is not the same as taking an ensemble average. In principle this non-commutativity is significant for a variety of quantities that we often use as observables and can lead to a bias in parameter estimation. We derive the relation between the ensemble average and the directional average of an observable, at second order in perturbation theory. We discuss the relevance of these two types of averages for making predictions of cosmological observables, focusing on observables related to distances and magnitudes. In particular, we show that the ensemble average of the distance in a given observed direction is increased by gravitational lensing, whereas the directional average of the distance is decreased. For a generic observable, there exists a particular function of the observable that is not affected by second-order lensing perturbations. We also show that standard areas have an advantage over standard rulers, and we discuss the subtleties involved in averaging in the case of supernova observations.
Forward citations
Cited by 4 Pith papers
-
Tetrad formalism for exact cosmological observables
The paper derives exact, coordinate-independent equations for cosmological observables on a new 'observer space-time' manifold, using tetrads to track the observer frame.
-
Gravitational redshift from large-scale structure: nonlinearities, antisymmetries, and the dipole
A wide-angle streaming model including gravitational redshift, lightcone and kinematic effects explains the dipole turnover at ~20 h^-1 Mpc as an advection-like shift driven by the density-weighted pairwise potential ...
-
Light path averages in spacetimes with non-vanishing average spatial curvature
Light-path averaged observables in Swiss cheese cosmologies show nearly the same mean and scatter in curved and flat FLRW backgrounds, indicating curvature does not significantly alter the relationship between line-of...
-
Les Houches on Dark Universe 2025: Elements of cosmology beyond FLRW
A lecture-notes review arguing that inhomogeneities cause only negligible backreaction and fitting corrections, leaving FLRW-based cosmology intact under the cosmological principle.
Discussion (0). Continue with ORCID to comment.