### Hubble time

**(t**_{H}, age of the universe)
(approximation of the age of the universe)

**Hubble time** (**t**_{H}) is a rough approximation
of the **age of the universe**,
specifically the reciprocal of the Hubble constant (H_{0}). Given the
current determination of H_{0} as 70 km/s/Mpc, the current
determination of *Hubble time* is 4.408 × 10^{17}
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/H_{0} 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.

(*constant,time,age*)
**Further reading:**

http://en.wikipedia.org/wiki/Hubble%27s_law

http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/hubble.html

**Referenced by pages:**

black hole merger

binary SMBH (BSMBH)

final parsec problem

Hubble constant (H_{0})

low mass star (LMS)

observable universe

Index