Curved space or curved vacuum?

While the simple Picture of a spatially flat, matter plus cosmological constant universe fits current observation of the accelerated expansion, strong consideration has also been given to models with dynamical Vacuum energy. We examine the tradeoff of curving the vacuum but retaining spatial flatness, vs. curving space but retaining the cosmological constant. These different breakdowns in the simple picture could readily be distinguished by combined high accuracy supernovae and cosmic microwave background distance Measurements. If we allow the uneasy situation of both breakdowns, the curvature can still be measured to No, but at the price of degrading estimation of the equation of state time variation by 60% or more, unless additional information (Such as weak lensing data or a tight matter density prior) is included. (c) 2005 Elsevier B.V. All rights reserved.