Supernovae, stellar explosions, have proven to be extremely useful distance indicators to map the expansion of the universe. There are three main cosmological applications of supernovae: measure the local expansion rate (Hubble constant), map the expansion history of the universe, which led to the discovery of the accelerated expansion, and a measurement of cosmic time dilation, which constitutes an independent proof that the universe expands.
A discrepancy of the local Hubble constant and the one derived from cosmic microwave background (at a redshift of roughly 1000) has led to the postulation of new components in the Universe. I will present the evidence for these results and critically discuss the uncertainties.
