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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 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.