Dark matter is a mysterious, non-luminous substance that is believed to constitute approximately 85% of the matter in the universe. Unlike ordinary matter, it does not emit, absorb, or reflect any electromagnetic radiation, making it invisible to all forms of light and direct observation. Its existence is inferred from its gravitational effects on visible matter, such as stars and galaxies. Without dark matter, galaxies would not have enough gravitational pull to hold themselves together, and they would fly apart. It is thought to be a crucial component in the formation and evolution of cosmic structures.
The concept of dark matter was first proposed by Swiss astronomer Fritz Zwicky in the 1930s. He observed that the galaxies in the Coma Cluster were moving much faster than could be explained by the amount of visible matter, suggesting the presence of a large amount of unseen "dunkle Materie" (dark matter). The idea gained more traction in the 1970s with the work of American astronomer Vera Rubin, who found that stars at the edges of galaxies were rotating at the same speed as those near the center, a violation of Newtonian physics that could be explained by a halo of dark matter surrounding the galaxy.
The search for the nature of dark matter is one of the most significant and active areas of research in modern physics and cosmology. Scientists are using a variety of direct and indirect detection methods to identify dark matter particles. Direct detection experiments are typically located deep underground to shield them from cosmic rays and are designed to detect the faint interactions of dark matter particles with atomic nuclei. Indirect detection methods search for the products of dark matter annihilation or decay, such as gamma rays or neutrinos, using space-based and ground-based telescopes. The discovery of the nature of dark matter would revolutionize our understanding of the universe and the fundamental laws of physics.