How strong is the evidence for accelerated expansion?

TL;DR

This paper assesses the evidence for the universe's accelerated expansion using supernova data without assuming specific matter-energy models, highlighting the influence of data choices and systematic errors on the results.

Contribution

It provides a model-independent test of cosmic acceleration, emphasizing the dependence of results on data set, fitting method, and calibration, and reports significant evidence for acceleration in flat universe models.

Findings

Strong 5 sigma evidence for acceleration in flat universe

Reduced 1.8 sigma evidence in open universe

Results highly sensitive to data and calibration choices

Abstract

We test the present expansion of the universe using supernova type Ia data without making any assumptions about the matter and energy content of the universe or about the parameterization of the deceleration parameter. We assume the cosmological principle to apply in a strict sense. The result strongly depends on the data set, the light-curve fitting method and the calibration of the absolute magnitude used for the test, indicating strong systematic errors. Nevertheless, in a spatially flat universe there is at least a 5 sigma evidence for acceleration which drops to 1.8 sigma in an open universe.