An Etymological Dictionary of Astronomy and Astrophysics

A → dimensionless number representing the ratio of various → physical constants. For example:

1. The ratio of the → Coulomb force to the → gravitational force for a proton-electron pair
   (e²/Gm_pm_e), which is of the order of 10⁴⁰.
   

2. The age of Universe (T = 10-20 x 10⁹ years) in units of the → elementary time: T/t_e≅ 10⁴⁰.
   

3. The square root of the total number of particles in the Universe ≅ 10⁴⁰.

See also: → large; → number.