The sign of this parameter differentiates between de Sitter and anti de Sitter space. It is multiplied by c squared and divided by 3 in one term of the Friedmann equation. Quantum field theory predicts it to be on the order of the Planck mass to the fourth and it is measured to be drastically smaller. This quantity minus half the scalar curvature multiplied by the metric tensor is proportional to the stress-energy tensor in the (*) Einstein field equations. This quantity found renewed relevance 
The sign of this parameter differentiates between de Sitter and anti de Sitter space. It is multiplied by c squared and divided by 3 in one term of the Friedmann equation. Quantum field theory predicts it to be on the order of the Planck mass to the fourth and it is measured to be drastically smaller. This quantity minus half the scalar curvature multiplied by the metric tensor is proportional to the stress-energy tensor in the (*) Einstein field equations. This quantity found renewed relevance when observations of type Ia ("one A") supernovae revealed that the universe's expansion was accelerating. For 10 points, name this parameter introduced by Albert Einstein to ensure that general relativity would still predict a static universe, often symbolized lambda.
The sign of this parameter differentiates between de Sitter and anti de Sitter space.
{cosmological constant} [accept {lambda} before mention]