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As it can be seen from Plank 2018 Cosmic Microwave Background temperature fluctuations data-

enter image description here

There are 3 sharp peaks at multipole expansions $\ell \approx 250, 550, 800 $. Also as multipole expansion goes on and adds more details to angular sensitivity of temperature fluctuations,- these fluctuations are damped-down almost exponentially. First question would be,- Why there are exactly 3 sharp peaks of CMB temperature fluctuations and what they are mapped to with respect to universe evolution timeline / structures/matter formation ? Are these peaks somehow related to the fact that universe is composed of ordinary matter, dark matter and dark energy, or this is irrelevant information ? And second question would be Why temperature fluctuations are decreased almost exponentially as multipole expansion goes on ? Thanks.

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    $\begingroup$ I’m no cosmologist and my understanding is limited, but here’s what I remember from my undergraduate cosmology class: first peak location on x axis is related to curvature of the universe, location of first peak on y axis is related to total mass density ($\Omega_M$), second peak y axis location related to baryonic matter (higher y value means less baryonic matter) and third peak y axis is related to dark matter amount. I have some very nice graphs illustrating this from my notes, but I have no idea what the source material is for it, that said I can share if you’re interested. $\endgroup$
    – Justin T
    Commented May 31, 2022 at 7:49
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    $\begingroup$ I would also add that I remember distinctly my professor saying this structure is some of the most compelling evidence we have for dark energy/ matter $\endgroup$
    – Justin T
    Commented May 31, 2022 at 7:54
  • $\begingroup$ Thanks, Can you expand on this in a bit more detailed version posting it in your answer ? $\endgroup$
    – Agnius Vasiliauskas
    Commented May 31, 2022 at 9:31

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