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Here, large-scale means (conceptually) the known universe. Hopefully, the data runs from (perhaps somewhat after) the Big Bang until now. Pointers to such results would be appreciated.

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Ordinary matter is directly observed astronomically, but dark matter is not. Since the ratio between dark matter and ordinary matter is calculated based on astronomical data about the orbit velocity of ordinary matter in galaxies, this ratio is very likely to remain unchanged over time. Since the nature of dark matter is unknown, it is perhaps possible (but not very likely) that it can over time change to unobservable radiation, and this would change the ratio.

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  • $\begingroup$ There are measurements of dark matter as function of redshift using gravitational lensing. So such data could exist. $\endgroup$
    – rfl
    Jan 26, 2023 at 23:46
  • $\begingroup$ Though yes, the ratio is expected to be constant over time, which would make a measurement all the more interesting $\endgroup$
    – rfl
    Jan 26, 2023 at 23:47

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