Cosmology Without the Fluid Approximation Work performed in collaboration with Pedro Ferreira. Timothy Clifton (University of Oxford, UK)

Small Scale Inhomogeneity Its convenient to treat many discrete sources as a continuous fluid. But does the continuous fluid have the same properties as the discrete set of objects?

Potential Pitfalls The averaging problem. The 'back-reaction' effect. Photon's travel through empty spaces between galaxies, not through a continuous energy density.

Potential Pitfalls The averaging problem. The 'back-reaction' effect. Photon's travel through empty spaces between galaxies, not through a continuous energy density. Area distance: Shear: Discrete points give R=0, C≠0. A continuous uniform fluid gives R≠0, C=0.

The Lindquist-Wheeler model Lattice model (inspired by Wigner-Seitz construction).

The Lindquist-Wheeler model Lattice model (inspired by Wigner-Seitz construction).

The Lindquist-Wheeler model Lattice model (inspired by Wigner-Seitz construction).

Expansion of Space Dynamics governed by the Friedmann equation. Scale of expansion approaches FRW as N→ ∞.

Optical Properties Calculate a photon trajectory passing through many cells: Integrate expansion scalar, and shear along trajectory. r L =r L (z)

Redshift The redshift-expansion relation can be different to FRW. Trajectories along lattice symmetries are special. Scatter around the average value is small at large z.

Luminosity Distance The luminosity-redshift relation is different to FRW. Typical trajectories are brighter at the same z. Trajectories along lattice symmetries can be dimmer.

Results Optical properties and dynamical properties of space-time do not approach a continuous limit in the same way. Redshifts can be altered from their FRW values. In the absence of shear, dimming can occur as a function of time, or brightening as a function of redshift (even as the continuous limit is approached). Some trajectories are strongly affected by shear, and optical scalars can diverge. Does not appear to behave as Dark Energy. Could have significant impact on CMB observations and precision cosmology.