The ratio of dark matter to regular matter in the universe is estimated to be approximately 5:1. This means that dark matter makes up about 80% of the total matter content in the universe, while regular matter (the stuff we can see and interact with) accounts for the remaining 20%.
Determining the existence and prevalence of dark matter is a complex scientific endeavor, and its nature is still not fully understood. Dark matter does not interact with electromagnetic radiation (such as light), making it invisible and difficult to detect directly. However, its presence can be inferred through its gravitational effects on visible matter and the large-scale structure of the universe.
There are several lines of evidence that support the existence of dark matter and provide estimates of its abundance:
Galactic Rotation Curves: Observations of the rotation curves of galaxies have shown that the visible matter alone cannot account for the observed speeds of stars and gas in galaxies. The gravitational effects of unseen matter, presumed to be dark matter, are needed to explain these observations.
Galaxy Cluster Dynamics: Studies of galaxy clusters, which are collections of galaxies bound together by gravity, have indicated that their high speeds of motion require the presence of significant amounts of dark matter. The observed gravitational lensing effects, where light from distant objects is bent by the cluster's gravity, also suggest the existence of dark matter.
Cosmic Microwave Background (CMB): Precise measurements of the cosmic microwave background radiation, the afterglow of the Big Bang, provide valuable information about the composition of the universe. The observed patterns in the CMB fluctuations support the idea that dark matter makes up a significant portion of the total matter content.
Large-Scale Structure: The distribution of galaxies and the large-scale structure of the universe can be simulated and compared to observations. These simulations require the inclusion of dark matter to reproduce the observed clustering patterns and formation of cosmic structures.
While we have strong indirect evidence for the existence and prevalence of dark matter, its exact nature remains elusive. Scientists are actively conducting experiments and observations to directly detect dark matter particles and further refine our understanding of this mysterious component of the universe.