If there is no dark matter, in order to explain our observations, our concepts of an important building
block of the universe have to be incorrect. What is that building block and why do Astronomers
overwhelmingly favor dark matter, which they cannot see, to explain our observations, rather than the
building block being incorrect?
The building block that Astronomers overwhelmingly favor is known as dark matter. Dark matter, as the name suggests, refers to a form of matter that does not interact with light or other forms of electromagnetic radiation, making it invisible to direct observation.
Astronomers rely on dark matter to explain various observations in the universe because there are several pieces of evidence that strongly suggest its existence. These pieces of evidence include:
1. Gravitational Effects: Dark matter is inferred to exist based on its gravitational effects on visible matter. Astronomers observe that the gravitational pull exerted by visible matter alone is not sufficient to explain the observed motions of stars and galaxies. By postulating the presence of invisible dark matter, they can reconcile these observations.
2. Galactic Rotation Curves: The rotation curve of a galaxy refers to how the velocity of stars or gas within the galaxy changes as a function of their distance from the galactic center. Observations of galaxy rotation curves show that stars and gas in galaxies rotate at increasingly higher velocities as their distance from the center increases. This suggests the presence of additional mass, attributed to dark matter, that extends beyond the visible regions of galaxies.
3. Large-Scale Structure: The distribution of galaxies in the universe is not uniform but clustered into large-scale structures like filaments and clusters. The formation of these structures can be explained by the gravitational influence of dark matter, which acts as a scaffolding on which visible matter accumulates.
4. Cosmic Microwave Background (CMB): The CMB is a faint radiation leftover from the early universe. Observations of the CMB by satellites such as the Planck spacecraft provide valuable insights into the composition and evolution of the universe. The patterns in the CMB strongly support the existence of dark matter, as it helps explain the observed distribution and fluctuations in the background radiation.
It's important to note that the favored explanation being dark matter does not necessarily mean that the concept of a building block of the universe is incorrect. Scientists continuously evaluate and refine their theories based on ongoing research and observations. However, dark matter has consistently provided the most compelling explanation for a wide range of astronomical observations, and alternative theories that can fully explain these observations without invoking dark matter have not yet gained sufficient evidence or consensus within the scientific community.