Universe Age
The Universe Age is the time elapsed since the big-bang, currently estimated at approximately 13.8 billion years. This metric serves as the fundamental temporal coordinate for cosmological models and the history of structure formation.
Key Milestones
- Planck Era & Inflation: Occurred within seconds to fractions of a second after the Big Bang, establishing initial conditions.
- Recombination & CMB: At ~380,000 years, electrons bound to nuclei, allowing photons to travel freely, creating the cosmic-microwave-background.
- Cosmic Dawn: The first stars and galaxies began forming between 100 million and 500 million years after the Big Bang.
Star Formation History
The rate of star formation across cosmic history is visualized via the madau-plot, which tracks the Stellar Mass Density over redshift.
- Peak Formation: Star formation rates peaked at “Cosmic Noon” (z ~ 2-3).
Age vs. Observable Size
A common cosmological paradox arises from the discrepancy between the universe’s age (~13.8 billion years) and the current diameter of the observable-universe (~92 billion light-years). This is resolved by understanding metric expansion:
- Light Travel Time vs. Proper Distance: While light has traveled for 13.8 billion years, the space it traversed has expanded during its journey.
- Current Radius: The comoving distance to the particle horizon is approximately 46 billion light-years, resulting in a diameter of ~92 billion light-years.
- Expansion Dynamics: The rate of expansion is governed by the Hubble Constant and the energy density of the universe (dark energy, matter, radiation).
For a detailed explanation of this discrepancy, see Observable Universe Expansion: Age vs. Current Size Explained.
References
- Observable Universe Expansion: Age vs. Current Size Explained (Fermilab, Dr. Don Lincoln)