Dark matter

Definition

Dark matter is a mysterious substance that makes up about 27% of the universe's total mass-energy content, yet it does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects on visible matter. Understanding dark matter is crucial for explaining the structure and evolution of the universe, as well as addressing significant gaps in current physical theories.

5 Must Know Facts For Your Next Test

1. The existence of dark matter is inferred from various astronomical observations, including the rotational speeds of galaxies and the gravitational lensing of light around massive objects.
2. Despite its prevalence, dark matter has yet to be directly detected through particle physics experiments, leading to ongoing research into its properties and candidates.
3. Dark matter plays a critical role in structure formation in the universe, influencing how galaxies and galaxy clusters form and evolve over time.
4. Models of cosmic evolution and the large-scale structure of the universe heavily rely on dark matter to explain the observed distribution of galaxies and clusters.
5. The search for dark matter includes both astrophysical observations and experiments at particle accelerators, highlighting the interplay between cosmology and particle physics.

Review Questions

• How do observations of galaxy rotation curves provide evidence for the existence of dark matter?
  • Observations show that galaxies rotate at speeds that suggest they should tear apart if only visible matter were present. However, the outer stars rotate at unexpectedly high speeds, implying there is additional unseen mass exerting gravitational influence. This discrepancy leads to the conclusion that dark matter must exist to account for the extra gravitational pull needed to hold galaxies together.
• Discuss the implications of dark matter on our understanding of the Standard Model of particle physics and where it falls short.
  • Dark matter poses significant challenges to the Standard Model, which accounts for only a fraction of the universe's total mass-energy content. While it successfully explains electromagnetic interactions and known particles, it does not include a viable candidate for dark matter. This limitation suggests that new physics may be required to understand dark matter's nature and its interactions beyond what is described by the Standard Model.
• Evaluate potential future experiments that could help uncover the nature of dark matter and their expected impact on particle physics.
  • Future experiments, such as those conducted at next-generation particle colliders and underground laboratories designed to detect WIMPs or other dark matter candidates directly, hold promise for revealing fundamental insights about dark matter. These investigations may lead to new particle discoveries or modifications to existing theories in particle physics. A successful identification of dark matter could revolutionize our understanding of the universe's composition, revealing new realms in both cosmology and particle physics.

Related terms

dark energy: A form of energy that is hypothesized to be responsible for the accelerated expansion of the universe, comprising about 68% of its total mass-energy content.

WIMPs: Weakly Interacting Massive Particles, a leading candidate for dark matter that interacts via the weak nuclear force and gravity, but not electromagnetically.

cosmic microwave background: Radiation left over from the Big Bang that provides a snapshot of the early universe and is influenced by the presence of dark matter.