The exact nature of dark energy has yet to be established. However, dark energy is believed to be extremely homogeneous (evenly spread throughout space) and of very low density, roughly 10-29 grams per cubic centimeter.
Various models of dark energy have been proposed, including a cosmic field associated with inflation; a different, low-energy field called quintessence; and the cosmological constant, or vacuum energy of empty space. Unlike Einstein's famous fudge factor, the cosmological constant in its present incarnation doesn't delicately (and artificially) balance gravity in order to maintain a static universe; instead, it has negative pressure that causes expansion to accelerate.
Related categories COSMOLOGY
• SPACE AND TIME
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