The ratio of dark matter to regular matter in the universe is estimated to be about 5:1. This means that dark matter makes up about 85% of the total matter content in the universe, while regular or "baryonic" matter (the matter that we can see and interact with) constitutes only about 15%.
Determining the ratio of dark matter to regular matter is a complex task, and it relies on a combination of observational data and theoretical modeling. Here are a few lines of evidence that support the existence and prevalence of dark matter:
Gravitational Effects: Dark matter is primarily inferred from its gravitational effects on visible matter and light. Observations of the rotation curves of galaxies, the motion of galaxy clusters, and the bending of light around massive objects (gravitational lensing) suggest the presence of additional mass that cannot be accounted for by visible matter alone.
Cosmic Microwave Background (CMB): The CMB is the remnant radiation from the early universe. Detailed measurements of the CMB, such as those made by the Planck satellite, provide information about the overall composition of the universe. The observations of the CMB support the existence of dark matter and provide constraints on its abundance.
Large-Scale Structure: The distribution of galaxies in the universe and the formation of large-scale structures can be explained by the gravitational influence of dark matter. Simulations that incorporate dark matter and its gravitational effects can reproduce the observed large-scale structure of the universe.
Collisions and Interactions: Although dark matter is generally invisible and does not interact electromagnetically, there have been attempts to directly detect it through its potential weak interactions with regular matter. Various experiments, such as those involving underground detectors or particle accelerators, are searching for signs of these interactions.
It's important to note that while dark matter's existence and prevalence are strongly supported by observational evidence, its exact nature and composition remain unknown. Scientists are actively studying and conducting experiments to further understand the properties and behavior of dark matter.