Large-scale structure of the Universe
Main article: Dark energyThe term dark energy can be used to refer to a subset of all causes of the observed accelerating expansion of the universe. In 1998, two Cosmology research teams, the High-Z Supernova Search Team and the Supernova Cosmology Project set out to measure the universe's rate of expansion which, according to Cosmological methods of the time, should have being slowing down as the immense gravitational pull generated by the Cosmic Web should have dominated over the expansion rate drawing the observable universe's contents back into a singularity as the Big Crunch predicted. Instead, via the measurement of very distant supernovae, Cosmologists deduced that the universe was expanding, and that the expansion rate was indeed uncontrollably accelerating, seemingly caused by an unknown spacetime phenomena now given the term dark energy. Dark Energy's nature is still unknown, even less well understood unlike the hypothetical dark matter. It is probably in the form of an exotic type of vacuum energy exerting negative pressure on the universe.