# What it the current value of the Hubble constant and why is the value so important?

Feb 21, 2016

${H}_{0} = 67.80 \setminus \pm 0.77 \setminus \quad k m . {s}^{- 1} . M p {c}^{- 1}$ (Planck Mission - 2013)
${H}_{0} = 69.32 \setminus \pm 0.80 \setminus \quad k m . {s}^{- 1} . M p {c}^{- 1}$ (WMAP Mission - 2012)

#### Explanation:

The value of the Hubble Parameter varies with time and so should not be called a constant. It is not a constant. However its value does not change appreciably in human time scales.

Though this is a fundamental cosmological parameter, estimating its value was always fraught with problems. Confusion regarding this resulted in the great debate between van den Bergh and Gustav Tammann in 1996.

Note : The debate was titled "The Scale Of The Universe" and was held at the Smithsonian's national museum of natural history.

van den Bergh argued for a higher value for the Hubble parameter around $80 \setminus \quad k m . {s}^{- 1} . M p {c}^{- 1}$ while Tammann argued for a lower value near $55 \setminus \quad k m . {s}^{- 1} . M p {c}^{- 1}$.

Prior to 1958 there were no reliable way of determining its value. The first reasonable estimate of the Hubble Constant was made by Alan Sandage in 1958. (${H}_{0} = 75 \setminus \quad k m . {s}^{- 1} M p {c}^{- 1}$).

Given below is a plot that shows the evolution of the Hubble Parameter estimate.