How is dark energy measured?

Dark energy is a mysterious force that pervades all space, acting as a "push" to accelerate the Universe's expansion. Despite being 70 percent of the Universe, dark energy was only discovered in 1998 by two teams observing Type Ia supernovae. read more

Dark energy also has a parameter called [math]w[/math], the equation of state parameter, This parameter describes how dark energy evolves with time. A value of [math] w = -1 [/math] indicates that dark energy is, in fact, a cosmological constant (and, to the best of our measurements, it appears to be so), instead of decreasing ([math] w > -1 [/math]) or increasing ([math] w < -1 [/math]). read more

The dark energy idea is essentially that the vacuum has a non-zero energy. The idea was proposed in order to fit the data of measurement of expansion of the universe when it appeared that the rate of expansion was accelerating. read more

The density of dark matter in an expanding universe decreases more quickly than dark energy, and eventually the dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved, but the density of dark energy is nearly unchanged (it is exactly constant in the case of a cosmological constant). read more