While the precise cause is not known, the observation is accepted as correct by the cosmologist community. By far the most accepted understanding is that this is due to an unknown form of energy which has been given the name "dark energy". "Dark" in this context means that it is not directly observed, but its existence can be deduced by examining the gravitational effect it has on the universe. Research is ongoing to understand this dark energy. Dark energy is now believed to be the single largest component of the universe, as it constitutes about 68.3% of the entire mass–energy of the physical universe.