Astrophysics (Index)About

Hubble time

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

Hubble time (tH) is basically the age of the universe. Often the term is used for an approximation (a back-of-the-envelope calculation) of the age of the universe consisting of the reciprocal of the Hubble constant (H0). Using an H0 value of 70 km/s/Mpc (roughly matching current determinations), Hubble time is 4.408 × 1017 seconds or 13.968 gigayears. Comparing a process's timescale to the Hubble time is a quick means of considering whether that process is likely to have completed: if a process's timescale is significantly longer, that constitutes evidence that a particular observation is unlikely to represent an example of that process. The final parsec problem regarding the likelihood of mergers of binary SMBHs illustrates such a comparison. (In such cases, the difference between 1/H0 and the universe's actual age is hardly significant and the term Hubble time is often used with no intention 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 13.813 Gy.


(constant,time,age)
Further reading:
https://en.wikipedia.org/wiki/Hubble%27s_law#Hubble_time
https://en.wikipedia.org/wiki/Age_of_the_universe
https://dictionary.obspm.fr/index.php?formSearchTextfield=Hubble+time&showAll=1
http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/hubble.html
https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095948568
https://astronomy.swin.edu.au/cosmos/h/Hubble+Law

Referenced by pages:
binary SMBH (BSMBH)
black hole merger
entropy (S)
final parsec problem
free streaming
galaxy age determination
Hawking radiation
Hubble constant (H0)
Hubble expansion
low mass star (LMS)
Milky Way (MW)
observable universe
Olbers' paradox
particle horizon
timescale (t)
valley of beta stability

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