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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 (Gy). 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 the completion 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.
The term Hubble time is sometimes used for the simple estimate of the universe's age, based upon Hubble's law, and sometimes is used for the actual age of the universe.