<Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (March 2014) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (March 2014) (Learn how and when to remove this template message) </Td> </Tr> <P> The Hubble constant H 0 (\ displaystyle H_ (0)) has units of inverse time; the Hubble time t is simply defined as the inverse of the Hubble constant, i.e. t H ≡ 1 H 0 = 1 67.8 (km / s) / Mpc = 4.55 ⋅ 10 17 s (\ displaystyle t_ (H) \ equiv (1 \ over H_ (0)) = (1 \ over 67.8 (\ textrm ((km / s) / Mpc))) = 4.55 \ cdot 10 ^ (17) (\ textrm (s))) = 14.4 billion years . This is slightly different from the age of the universe t 0 ≈ (\ displaystyle t_ (0) \ approx) 13.8 billion years . The Hubble time is the age it would have had if the expansion had been linear, and it is different from the real age of the universe because the expansion isn't linear; they are related by a dimensionless factor which depends on the mass - energy content of the universe, which is around 0.96 in the standard Lambda - CDM model . </P> <P> We currently appear to be approaching a period where the expansion is exponential due to the increasing dominance of vacuum energy . In this regime, the Hubble parameter is constant, and the universe grows by a factor e each Hubble time: </P>

The relationship of the two parameters in the hubble law indicate that