Technical definition Dark matter

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in standard cosmology, matter energy density scales inverse cube of scale factor, i.e. ρ ∝ a. in contrast radiation, scales inverse fourth power of scale factor ρ ∝ a, , dark energy, unaffected ρ ∝ a. can understood intuitively: ordinary particle in square box, doubling length of sides of box decreases density (and hence energy density) factor of 8 (2). radiation, decrease in energy density greater, because increase in spatial distance causes redshift. dark energy, intrinsic property of space, has constant energy density regardless of volume under consideration.


dark matter component of universe not ordinary matter, still obeys ρ ∝ a.








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