What does Hubble's constant represent?

Mar 15, 2018

It represents the ratio between the recessional velocity of a galaxy ($k m$ ${s}^{-} 1$) and the distance to the galaxy ($\text{Mpc}$), $k m$ ${s}^{-} 1$ $M p {c}^{-} 1$, or sometimes converted to ${s}^{-} 1$. When given in terms of ${s}^{-} 1$, $\frac{1}{H} _ 0 = \text{approximate age of the universe}$

Explanation:

Based on observations, we know that $v \propto d$ with $v$ being recessional velocity($k m$ ${s}^{-} 1$) and $d$ being distance (Mpc#)

A graph of $v$ against $d$ produces a rough straight line with gradient ${H}_{0}$, using this we can work out the recessional velocity or distance to a galaxy given the other.

$\text{time"="distance"/"velocity} = \frac{1}{H} _ 0$

When ${H}_{0}$ is given as ${s}^{-} 1$ the reciprocal can give the approximate age of the universe.