"Experimental proof for the observable universe being a "zero-energy universe" **is currently inconclusive**. Gravitational energy from visible matter accounts for 26–37% of the observed total mass-energy density. Therefore to fit the concept of a "zero-energy universe" to the observed universe, other negative energy reservoirs besides gravity from baryonic matter are necessary. These reservoirs are frequently assumed to be dark matter" Source: Wikipedia (Zero-Energy Universe)
