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They say that the total energy of the universe consists of 4.9\% ordinary matter, 26.8\% dark matter and 68.3\% dark energy. I hear this pie part in virtually every lecture in cosmology. How do we know these numbers?enter image description here

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These numbers are determined by fitting precise observational data of the small anisotropies of the cosmic microwave background, gathered by the Planck spacecraft, to the standard model of cosmology, the Lambda-CDM model.

In this successful model based on the Friedmann equations, there are three ingredients that make up the contents of our universe: dark energy (that’s the “Lambda”), “cold” (i.e., non-relativistic) dark matter (that’s the “CDM”), and ordinary matter. Radiation provides a negligible fraction of the current energy density.

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  • $\begingroup$ So these values are determined by fitting them as input parameters inthe model and optimizing? $\endgroup$ – mithusengupta123 May 10 at 4:56
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    $\begingroup$ As you can see in the “Parameters” section of Wikipedia’s Lambda-CDM article, this model has six independent parameters as inputs, but they don’t include these pie chart numbers. Instead, those three values are outputs among 10 calculated values. The “successes” section discusses how this model fits various peaks in the so-called TT spectrum, and then predicts various peaks in the TE and EE spectra, which are observed. $\endgroup$ – G. Smith May 10 at 5:06

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