<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> In physical cosmology and astronomy, dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe . Dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is expanding at an accelerating rate . </P> <P> Assuming that the standard model of cosmology is correct, the best current measurements indicate that dark energy contributes 68.3% of the total energy in the present - day observable universe . The mass--energy of dark matter and ordinary (baryonic) matter contribute 26.8% and 4.9%, respectively, and other components such as neutrinos and photons contribute a very small amount . The density of dark energy (~ 7 × 10 g / cm) is very low, much less than the density of ordinary matter or dark matter within galaxies . However, it dominates the mass--energy of the universe because it is uniform across space . </P> <P> Two proposed forms for dark energy are the cosmological constant, representing a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space . Contributions from scalar fields that are constant in space are usually also included in the cosmological constant . The cosmological constant can be formulated to be equivalent to the zero - point radiation of space i.e. the vacuum energy . Scalar fields that change in space can be difficult to distinguish from a cosmological constant because the change may be extremely slow . </P>

Where does the dark reaction get its energy from
find me the text answering this question