Astrophysics (Index)About

Hubble time

(tH, age of the universe)
(approximation of the age of the universe)

Hubble time (tH) is a rough approximation of the age of the universe, specifically the reciprocal of the Hubble constant (H0). Given the current determination of H0 as 70 km/s/Mpc, the current determination of Hubble time is 4.408 × 1017 seconds or 13.968 gigayears. Comparing a process's timescale to the Hubble time as a quick means of considering whether the process is likely to have completed: if something's timescale is significantly longer, that is evidence that an observation is not an example of the process. For example, the final parsec problem regarding the likelihood of mergers of binary SMBHs. (In such cases, the discrepancy between 1/H0 and the actual age is of no significance and someone might use the term Hubble time with no intent of distinguishing it from the actual age.)

A more accurate age of the universe determination requires general relativity adjustments taking into account the redshift effects of gravity and/or expansion effects of dark energy. For some time, determinations have been near 13.8 Gy and a 2015 determination based on data from the Planck mission puts it at 13.799 Gy.

Further reading:

Referenced by pages:
black hole merger
binary SMBH (BSMBH)
final parsec problem
Hubble constant (H0)
low mass star (LMS)
observable universe