Properties of Dark Energy

Einstein’s cosmological constant  has the property that P = -  = -1. Significant quantities of matter-energy with “negative pressure” will cause the expansion of the universe to accelerate.
The quantity P/= w is known as the “equation of state” parameter. Best measurements right now (WMAP and others) find that w = -1, consistent with the value expected for the “concordance model” aka CDM (cosmological constant + cold dark matter)

Einstein’s cosmological constant  has the property that P = -  = -1. Significant quantities of matter-energy with “negative pressure” will cause the expansion of the universe to accelerate.