Question

Explain how CMB data can be used to determine the dark matter content of the Universe.

Answer 1

First we should know that Dark Matter is a form of matter thought to be present approximately 85 percent of the matter in the universe and about 1/4th of its total energy density. Primary evidence for dark matter comes from calculations showing that many galaxies would fly apart, or that they would not have formed or would not move as they do, if they did not contain a large amount of unseen matter. Now many development has been made too in the gravitational theory of Dark Matter.

On the other hand, CMB(Cosmic Microwave Background) is the oldest electromagnetic radiation in the universe, which is very much helpful to calculate different space and universe structural evidence and presence too.

​​​​​​In this way CMB data can be helpful in determining the dark matter content in the universe too. There is an effect of Dark Matter on CMB as the dark matter not like ordinary matter does not interact directly with radiation, but it does affect the CMB by its gravitational potential and by its effects on the density and velocity of ordinary matter. Ordinary and dark matter perturbations, therefore, evolve differently with time and leave different imprints on the cosmic microwave background (CMB). Dark Matter's existence is calculated through CMB in planck's space craft through Lambda-CDM model in 2013-15. This model gives complete evidence of Dark Matter content in the universe too. Hence, CMB is very much useful in finding the evidence of Dark Matter's content.

Thank you (^_-)