The age of the universe can be estimated using several techniques.

1. Radioactive dating yields an age of the solar system of about 4.6 billion years. This is a measure of the time since solidification.

2. globular cluster Hertzsprung-Russell diagram fitting yields an age of 9-18 billion years.

3. The Hubble method, taking where H is the Hubble constant, yields 15 billion years.

Cosmology, Curvature of the Universe, Expansion of the Universe, Hubble Constant