Is the expansion of the universe accelerating? All signs point to yes
  The accelerating expansion of the universe is one of the most profound
discoveries in modern cosmology, pointing to a universe in which 70% of the
mass-energy density has an unknown form spread uniformly across the universe.
This result has been well established using a combination of cosmological
probes (e.g., Planck Collaboration et al. 2016), resulting in a "standard
model" of modern cosmology that is a combination of a cosmological constant
with cold dark matter and baryons. The first compelling evidence for the
acceleration came in the late 1990's, when two independent teams studying type
Ia supernovae discovered that distant SNe Ia were dimmer than expected. The
combined analysis of modern cosmology experiments, including SNe Ia, the Hubble
constant, baryon acoustic oscillations, and the cosmic microwave background has
now measured the contributions of matter and the cosmological constant to the
energy density of the universe to better than 0.01, providing a secure
measurement of acceleration. A recent study (Tr{\o}st Nielsen et al. 2015) has
claimed that the evidence for acceleration from SNe Ia is "marginal." Here we
demonstrate errors in that analysis which reduce the acceleration significance
from SNe Ia, and further demonstrate that conservative constraints on the
curvature or matter density of the universe increase the significance even
more. Analyzing the Joint Light-curve Analysis supernova sample, we find
4.2{\sigma} evidence for acceleration with SNe Ia alone, and 11.2{\sigma} in a
flat universe. With our improved supernova analysis and by not rejecting all
other cosmological constraints, we find that acceleration is quite secure.
