Universe opacity and Type Ia supernova dimming

In this paper, I revoke a debate about an origin of Type Ia supernova (SN Ia) dimming. I argue that except for a commonly accepted accelerating expansion of the Universe, a conceivable alternative for explaining this observation is universe opacity caused by light extinction by intergalactic dust, even though it is commonly assumed that this effect is negligible. Using data of the Union2.1 SN Ia compilation, I find that the standard $\Lambda$CDM model and the opaque universe model fit the SN Ia measurements at redshifts $z < 1.4$ comparably well. The optimum solution for the opaque universe model is characterized by the B-band intergalactic opacity $\lambda_B = 0.10 \pm 0.03 \, \mathrm{Gpc}^{-1}$ and the Hubble constant $H_0 = 68.0 \pm 2.5 \, \mathrm{km\,s^{-1}\, Mpc^{-1}}$. The intergalactic opacity is higher than that obtained from independent observations but still within acceptable limits. This result emphasizes that the issue of the accelerating expansion of the Universe as the origin of the SN Ia dimming is not yet definitely resolved. Obviously, the opaque universe model as an alternative to the $\Lambda$CDM model is attractive, because it avoids puzzles and controversies associated with dark energy and the accelerating expansion.