By: Jeremy Sun

By the late 1920s, astronomers used Newton and Einstein’s theories to understand the universe’s structures and list stars and galaxies. But in the early 1930s, a big discovery changed everything: dark matter. Astronomers like Jan Oort and Fred Zwicky noticed that some cosmic structures were moving too fast for their visible mass to hold them together, suggesting an unseen mass. This mystery, called “dark matter,” has become a key part of astrophysics. Finding out what dark matter is will help us understand the basic laws of the universe.

Usually, when astronomers find new phenomena, they gather better data until they understand it. But since dark matter can’t be seen, they had to rely on indirect observations. From the 1960s to the 1980s, detailed maps of galaxy speeds showed that dark matter is usually spread out within galaxies and extends beyond the visible stars. This suggested that dark matter halos are much larger than the visible parts of galaxies.

By the 1980s, many theories tried to explain the missing mass. Some suggested that non-luminous objects like black holes or planet-sized rocks could be the dark matter, but studies mostly ruled this out. Despite the lack of agreement on dark matter properties, many scientists are dedicated to searching for this elusive particle. Observations of light from the early universe indicated that most of the matter then did not interact strongly with normal matter. This pointed to the existence of non-baryonic matter, suggesting unknown particles might explain the excess mass without interacting noticeably with normal matter.

Currently, most astrophysicists agree that at least one new kind of particle is needed to explain dark matter. These particles must have mass and interact very rarely with ordinary matter, such as atoms, and with other forces or particles in the universe. Despite decades of research, many theories are still viable, some of which are hard to test with current technology. However, several ongoing experiments aim to explore different possibilities for these unknown particles.

Dark matter detection experiments aim to capture as many potential interactions as possible, searching for rare events over long periods. Accelerator-based searches focus on high-energy collisions, while telescope-based searches look for specific high-energy light bursts from hypothesized dark matter decays. Direct detection experiments rely on ambient dark matter interacting with detectors on Earth, requiring large and heavy detectors to increase potential interactions.

Beyond these observations, dark matter is crucial for understanding how the universe evolved from a uniform, hot plasma to its current structured state. Detecting dark matter and understanding its properties could help determine which theories about the universe’s evolution are correct. Although we have only ruled out certain possibilities, the boundaries established by the elimination of certain possibilities in the search for understanding dark matter have helped refine dark matter theories.

However, the true significance of dark matter lies in its properties, which could transform our understanding of physical laws. This pursuit, blending faith and knowledge, is a fundamental aspect of the scientific process and reflects our quest to comprehend the universe’s mysteries.

Image Credit by Monica Oprea