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Parameters that quantify the acceleration of cosmic expansion are conventionally determined within the standard Friedmann-Lemaître-Robertson-Walker (FLRW) model, which fixes spatial curvature to be homogeneous. Generic averages of Einstein's equations in inhomogeneous cosmology lead to models with non-rigidly evolving average spatial curvature, and different parametrizations of apparent cosmic acceleration. The timescape cosmology is a viable example of such a model without dark energy. Using the largest available supernova data set, the JLA catalogue, we find that the timescape model fits the luminosity distance-redshift data with a likelihood that is statistically indistinguishable from the standard spatially flat Λ cold dark matter cosmology by Bayesian comparison. In the timescape case cosmic acceleration is nonzero but has a marginal amplitude, with best-fitting apparent deceleration parameter, q 0 = −0.043−0.000 . Systematic issues regarding standardization of supernova light curves are analysed. Cuts of data at the statistical homogeneity scale affect light curve parameter fits independent of cosmology. A cosmological model dependence of empirical changes to the mean colour parameter is also found. Irrespective of which model ultimately fits better, we argue that as a competitive model with a non-FLRW expansion history, the timescape model may prove a useful diagnostic tool for disentangling selection effects and astrophysical systematics from the underlying expansion history.Key words: cosmological parameters -dark energy -cosmology: observationscosmology: theory INHOMOGENEOUS ALTERNATIVES TO DARK ENERGYOne of the most important discoveries in cosmology (Riess et al. 1998;Perlmutter et al. 1999) is the observation that the luminosity distances and redshifts of type Ia supernovae (SneIa) are well matched to the expansion history of a spatial homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker (FLRW) model only if the Universe began an epoch of accelerated expansion late in cosmic history. Since gravity with matter obeying the Strong Energy Condition is universally attractive, this demands a cosmological constant, Λ, or some other unknown source of spatially homogeneous dark energy with an equation of state, P = wρc 2 , that subsequent tests find to be close to the cosmological constant case, w = −1. Independently of SneIa, since the late 1990s other data sets including the cosmic microwave background (CMB) and galaxy clustering statistics, have been found to independently require late epoch cosmic acceleration in the FLRW model.

We present the luminosity distance series expansion to third order in redshift for a general space-time with no assumption on the metric tensor or the field equations prescribing it. It turns out that the coefficients of this general Hubble law can be expressed in terms of a finite number of physically interpretable multipole coefficients. The multipole terms can be combined into effective direction dependent parameters replacing the Hubble constant, deceleration parameter, curvature parameter, and jerk parameter of the Friedmann-Lemaître-Robertson-Walker (FLRW) class of metrics. Due to the finite number of multipole coefficients, the exact anisotropic Hubble law is given by 9, 25, 61 degrees of freedom in the 𝒪(z), 𝒪(z2), 𝒪(z3) vicinity of the observer respectively, where z:=redshift. This makes possible model independent determination of dynamical degrees of freedom of the cosmic neighbourhood of the observer and direct testing of the FLRW ansatz. We argue that the derived multipole representation of the general Hubble law provides a new framework with broad applications in observational cosmology.