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According to the article "Dark Matter" https://en.wikipedia.org/wiki/Dark_matter the current Lambda-CDM model estimates the total mass-energy content of the universe consists of 68.2% dark energy, 26.8% dark matter, and 5% baryonic matter.

Are there accuracy estimates for each of these quantities (perhaps derived from observational errors, such as measurement errors of the Planck spacecraft)?

Are there hypotheses which try and explain why this particular distribution (or something close to it) makes sense? To the extent that the hypotheses are based on observed quantities, can we derive goodness-of-fit estimates for them -- do these fit within the accuracy estimates of the energy proportions in Lambda-CDM?

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Yes, all of these estimates have uncertainties. Table 2 of Planck Collaboration (2021) are the most recently compiled results. The exact values depend on which datasets go into the estimates.

There are no (widely accepted) hypotheses as to why we live in a universe that currently has this particular mixture. Note that the mixture is time-dependent - whilst the ratio of dark to baryonic matter is fixed, the ratio of dark energy to matter is increasing with time.

There are of course anthropic arguments that one can make about why we are alive and the Earth exists - because that would be unlikely for certain ranges of values for these parameters. But why for instance the ratio of dark to baryonic matter is 5, rather than say 4, is still a mystery and so there is no model to test.

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  • $\begingroup$ whilst the ratio of dark to baryonic matter is fixed There are people working on theories where dark matter decays, though. (No idea if matter decaying into dark matter is a thing. Maybe?) $\endgroup$
    – Allure
    Jun 12, 2023 at 5:31

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