Does small scale structure significantly affect cosmological dynamics?

Understand

The large-scale homogeneity and isotropy of the universe is generally thought to imply a well defined background cosmological model.

• It may not.
• Smoothing over structure adds in an extra contribution, transferring power from small scales up to large.
• Second-order perturbation theory implies that the effect is small, but suggests that formally the perturbation series may not converge.