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Implications of Non-Fluid Cosmology: A Study of Small Scale Inhomogeneities and Optical Properties

Explore the limitations of fluid approximation in cosmology, analyzing discrete vs. continuous sources, potential pitfalls like the 'back-reaction' effect, and insights into space-time dynamics and optical properties.

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Implications of Non-Fluid Cosmology: A Study of Small Scale Inhomogeneities and Optical Properties

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

  2. 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?

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

  4. 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.

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

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

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

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

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

  10. 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.

  11. 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.

  12. 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.

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