Dark Matter and Dark Energy

I. Dark Matter

Dark matter is a special form of matter that exists widely in the universe but cannot be directly observed. It is a key component of cosmic structure.

Its most essential characteristic is that it has no electromagnetic properties: it neither emits light, nor absorbs light, nor reflects or scatters light. Therefore, it cannot be detected by optical telescopes, radio telescopes, or other equipment that relies on electromagnetic waves. However, dark matter possesses real mass and exerts gravitational effects, which is the only way we can perceive its existence.

In the universe, dark matter does not form dense celestial bodies such as stars and planets like ordinary matter, nor does it undergo physical reactions such as collision or condensation. It mostly gathers around galaxies in a diffuse state, forming gravitational constraints that hold celestial bodies within galaxies together and prevent galaxies from disintegrating due to high-speed rotation. It moves slowly and is stable in nature, serving as an important framework for constructing large-scale cosmic structures. It only interacts gravitationally and most likely weakly, with no other interactions with other forms of matter.

II. Dark Energy

Dark energy is not matter in the traditional sense, but background energy that uniformly fills the entire space of the universe. It is the core force driving cosmic evolution.

It has no mass, no definite structure, and no fixed position. It is evenly distributed throughout the universe, and its energy density remains constant without being diluted as the universe expands. Dark energy does not interact electromagnetically or strongly. It does not produce gravitational attraction; instead, it has negative pressure and generates universal repulsion. This repulsion can counteract and surpass the gravitational attraction between matter, pushing cosmic space to expand continuously at an accelerating rate.

Unlike dark matter, dark energy cannot form any cosmic structure, nor can it serve as a reference point for space. It cannot define position or motion. It only acts on pre-existing spacetime and simply drives spatial expansion.