Dark matter and dark energy are theoretical concepts used to explain certain observations in cosmology, although their precise nature remains unknown. Here's a brief overview of their properties and their interactions with the known particles of the standard model of particle physics and the fundamental forces of nature:
- Dark Matter: Dark matter refers to an invisible and non-luminous form of matter that does not interact with electromagnetic radiation. It is called "dark" because it does not emit, absorb, or reflect light, making it undetectable using traditional astronomical methods.
Properties:
- Dark matter is believed to be much more abundant than visible matter in the universe, constituting approximately 85% of the total matter content.
- It interacts gravitationally and contributes to the observed gravitational effects on galaxies and galaxy clusters.
- It is thought to be "cold" in nature, meaning its constituent particles move relatively slowly compared to the speed of light.
Interaction with the Standard Model:
- Dark matter does not interact via the electromagnetic force, which means it does not interact with photons or charged particles.
- It does not participate in the strong nuclear force, which binds atomic nuclei.
- Dark matter likely interacts only through gravity and possibly weak nuclear force interactions, which are responsible for some forms of radioactive decay.
- Dark Energy: Dark energy is a hypothetical form of energy that is postulated to explain the observed accelerated expansion of the universe. Unlike dark matter, dark energy is not considered to be composed of particles but is thought to be an inherent property of space itself.
Properties:
- Dark energy is believed to constitute approximately 70% of the total energy content of the universe.
- It is characterized by negative pressure, causing it to exert a repulsive gravitational effect.
- Dark energy is thought to be uniformly distributed throughout space and its density remains constant as the universe expands.
Interaction with the Standard Model:
- Dark energy is hypothesized to act as a property of space itself, influencing the expansion of the universe.
- It does not directly interact with known particles of the standard model or the fundamental forces.
- Dark energy's effects are primarily observed on the large-scale structure of the universe, driving the accelerated expansion and affecting the distribution of galaxies.
It's important to note that the exact nature of dark matter and dark energy is still a subject of ongoing research and investigation. Various theoretical models and candidates have been proposed, but their definitive identification and understanding remain elusive.