Cosmic Expansion
Core Definition: Metric expansion of space characterized by increasing proper distance between gravitationally unbound regions over time. Fundamental component of the big-bang cosmology and Lambda-CDM Model.
Dynamics & Drivers
- Mechanism: Expansion dynamics described by Friedmann Equations; current accelerated phase attributed to Dark Energy ().
- Parameters: Expansion rate quantified by the Hubble Constant (); spatial geometry constrained by Curvature of the Universe measurements.
- Observables: Inferred via Redshift surveys, Type Ia Supernovae, and Cosmic Microwave Background anisotropies.
Observable Universe Scale & Horizon
- Age-Size Paradox: The observable universe has a current proper radius of ~46 billion light-years, despite the universe being only ~13.8 billion years old. This discrepancy arises because space itself expanded while photons traveled from distant sources to the observer.
- Particle Horizon: The limit of causal contact is defined by the particle horizon, which grows faster than the speed of light in comoving coordinates due to metric expansion.
- Source Analysis: Detailed explanation of this geometric effect is provided in Observable Universe Expansion: Age vs. Current Size Explained.
References
- Observable Universe Expansion: Age vs. Current Size Explained (Fermilab, Dr. Don Lincoln)