On the Green and Wald formalism

Understand

Backreaction in the cosmological context is a longstanding problem that is especially important in the present era of precise cosmology.

• The standard model of a homogeneous background plus density perturbations is most probably oversimplified and is expected to fail to fully account for the near-future observations of sub-percent precision.
• From a theoretical point of view, the problem of backreaction is very complicated and deserves careful examination.
• Recently, Green and Wald claimed in a series of papers to have developed a formalism to properly describe the influence of density inhomogeneities on average properties of the Universe, i.e., the backreaction effect.