Definition
Dark Matter is a hypothetical form of matter that is thought to account for approximately 85% of the matter in the universe and about 25% of its total energy density. It is “dark” because it does not appear to interact with the electromagnetic field, meaning it does not absorb, reflect, or emit light, making it difficult to detect.
Why It Matters
Dark matter is the invisible “scaffolding” that holds galaxies together. Without it, the universe as we know it would not exist, making its detection and study vital for a complete understanding of gravity and cosmic structure.
Core Concepts
- Gravitational Evidence: Its presence is inferred from gravitational effects on visible matter, such as the rotation speeds of galaxies and the gravitational lensing of light.
- WIMPs (Weakly Interacting Massive Particles): A leading class of candidate particles that would interact only through gravity and the weak force.
- Cold Dark Matter (CDM): The standard model of cosmology (Lambda-CDM) assumes dark matter is “cold,” meaning it moves much slower than the speed of light.
- Missing Link: While its effects are clear at galactic and cosmological scales, no dark matter particle has yet been directly detected in laboratory experiments.