Age of the universe

The time elapsed since the universe began expanding from its hot, dense early state, estimated at about 13.8 billion years.

Hubble constant: The present rate at which the universe's expansion increases the distance between distant galaxies. Its value sets the expansion rate used to infer cosmic age.
Big Bang: The expansion of the universe from an early hot, dense state into its present condition. The age measures time since this early expansion began.
Hubble tension: The persistent disagreement between early-universe and local measurements of the Hubble constant. Different expansion rates imply different inferred ages within a given cosmological model.
Planck 2018 results: The final major cosmological parameter analysis from the Planck satellite's observations of the cosmic microwave background. Its standard-model fit gives an age of about 13.8 billion years.
Friedmann equations: Equations in general relativity that describe how the universe's expansion changes over time. They connect cosmic contents and expansion history to the elapsed time.
Metric expansion of space: The increase in distances between unbound objects as the universe's spatial scale grows. The universe's expansion history is central to calculating elapsed cosmic time.
Globular cluster age: An estimate of a globular cluster's age from the evolution of its stars. The oldest clusters provide a lower bound that an expansion-derived age must exceed.
Cosmic distance ladder: A sequence of calibrated astronomical methods for measuring distances beyond the Solar System. Its local expansion measurements contribute to age estimates and the Hubble tension.
Cosmic microwave background: The relic radiation released when the early universe became transparent, now observed as microwave light. Its measured patterns constrain the parameters used to calculate the age.
General relativity: Albert Einstein's theory describing gravity as the curvature of spacetime caused by matter and energy. It supplies the gravitational framework for models of cosmic expansion.

Linked from 10 pages