Dark matter and normal matter are distinct components of the universe with several key differences.
Composition: Normal matter, which includes atoms, is made up of particles such as protons, neutrons, and electrons. These particles interact through electromagnetic forces and form the building blocks of familiar objects like stars, planets, and living organisms. In contrast, dark matter is hypothesized to consist of non-baryonic particles that do not interact via electromagnetic forces. The exact nature of dark matter particles is still unknown, but they are believed to be more massive and weakly interacting.
Visibility: Normal matter interacts with electromagnetic radiation, allowing it to emit, absorb, and scatter light. This interaction makes normal matter visible and detectable through various instruments and telescopes. Dark matter, as the name implies, does not interact with light or other electromagnetic radiation, making it invisible and challenging to directly observe.
Distribution: Dark matter is believed to be far more abundant than normal matter in the universe. According to current models, dark matter makes up about 85% of the total matter in the universe, while normal matter constitutes only around 15%. The precise reasons for this asymmetry are still the subject of scientific investigation.
The predominance of dark matter over normal matter in the universe arises from a combination of factors:
Primordial Nucleosynthesis: During the early stages of the universe, shortly after the Big Bang, conditions were such that the formation of helium and other light elements was favored. The abundance of normal matter was set during this period. Dark matter, on the other hand, does not participate in these processes and thus remained unaffected.
Gravitational Clustering: Dark matter interacts predominantly through gravitational forces, enabling it to clump together and form large-scale structures such as galaxies and galaxy clusters. Normal matter, due to its electromagnetic interactions, experiences additional forces that can hinder gravitational collapse. As a result, dark matter forms the scaffolding on which normal matter gathers, leading to the observed distribution of matter in the universe.
Dark Matter's Non-Interacting Nature: The lack of strong interactions between dark matter particles means they can pass through each other and normal matter without significant scattering or collision. This property allows dark matter to accumulate in vast quantities over cosmic timescales, while normal matter is subject to various forces that can disperse or dissipate it.
Despite the differences between dark matter and normal matter, both play crucial roles in shaping the structure and evolution of the universe. Researchers continue to study and investigate dark matter to unravel its mysteries and understand its profound influence on cosmic phenomena.