For 10 points, name this quantity, which Einstein called his "biggest blunder."
Like the scalar curvature, this quantity is multiplied by the metric tensor in Einstein's field equations. Although quantum field theory predicts a property that could be represented by this, QFT predictions for its value do not match cosmological ones, causing this property's namesake problem. Introducing this parameter into the FriedmannRobertsonWalker metric gives the standard Lambda-CDM model. This entity contrasts with quintessence and other forms of dark energy because it is constant and equal at all points in the universe. This quantity, equivalent to the energy density of empty space, was first proposed by Einstein to allow for a static universe in general relativity. For 10 points, name this quantity, which Einstein called his "biggest blunder."
Like the scalar curvature, this quantity is multiplied by the metric tensor in Einstein's field equations.
cosmological constant [prompt on lambda]