What's the explanation for the cosmological constant?

Answer 1

In physical cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. Einstein abandoned the concept after the observation of the Hubble redshift indicated that the universe might not be stationary. However, the discovery of cosmic acceleration in the 1990s has renewed interest in a cosmological constant.

Here is some good info with details http://en.wikipedia.org/wiki/Cosmological_constant

Answer 2

The cosmological constant represents the energy that causes space to expand. At present it's just an empirically derived factor. There are various hypotheses about the nature and origin of the expansive force, but no well-developed theory.

Answer 3

Nothing. We don't have one. We do have an increasing data set indicating that the current universe is accelerating which can be modeled with either the cosmological constant or a dark energy term. Either are indications that general relativity is giving us a hint at something that lies beyond its predictive capacity, but we have not found a theoretical or experimental effect that would explain rather than just model the acceleration.

Answer 4

there is not one single explanation for it, but as i understand it (i'm not a cosmologist) there are several hypotheses including dark energy and quintessence. the wikipedia page quoted above should have more info.