•Density
contrast depends on size scale:
–Galaxies a
million times higher than average
–Clusters a
thousand times higher than average
–Superclusters
a few times higher than average
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•Average density
varies as (1+z)3,
so at z=100 (a
matter-dominated epoch), galaxies had ∆=∂ρ/ρ=1 and could not have
formed at higher z. Clusters and
superclusters had to form at much lower z.
Formation of structure is in principle accessible.
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