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

Answer 1

#H_0 = 67.80 \pm 0.77 \quad km.s^{-1}.Mpc^{-1}# (Planck Mission - 2013)
#H_0 = 69.32 \pm 0.80 \quad km.s^{-1}.Mpc^{-1}# (WMAP Mission - 2012)

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\quad km.s^{-1}.Mpc^{-1}# while Tammann argued for a lower value near #55 \quad km.s^{-1}.Mpc^{-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\quad km.s^{-1}Mpc^{-1}#).

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

Image Source : https://tutor.hix.ai

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Answer 2

Olivia Aldridge

The rate of expansion of the universe is represented by the Hubble constant, which is currently estimated to be 67.4 km/s/Mpc. This value is significant because it aids in the determination of the universe's age, size, and destiny, as well as offering insights into basic cosmological concepts and the nature of dark energy.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.