Hubble's Law



In the 1920's the American astronomer, Edwin Hubble, amassed data from spectroscopic studies of galaxies, that showed that galaxies are generally moving away from earth, and their velocities are greater the farther away they are. Daskalakis notes (2005, p.201) that Hubble stated in his book Realm of Galaxies that this can be explained if the earth is at the center of a finite spherical universe. However, Hubble went on to explain that if the reason behind the data was not velocity shifts, the data can be explained by a principle that the universe is expanding, and its expansion makes the redshifts. This possible expansion confirmed a theory of an expanding universe which the Russian cosmologist Alexander Friedman had presented in 1922.

Hubble's Law states that the recessional velocity (v) of objects in the universe is proportional to its distance (D) from us.

v=H0D

Thus he believed that there is some constant, now known as the Hubble Constant (H0) which when multiplied by the distance to the object (D) would give you the apparent velocity of the object and from that its redshift.

Derivation And Interpretation
This formula is derived by plotting the measured redshift of Extra-Galactic-Nebula against its distance. The linearity of the plot is used to prove that the universe is expanding.

Mistakes
There are several mistakes in the derivation.

Distance
If astronomers do not know how to calculate the distance of far-away objects in the universe, this plot is meaningless. For example Hubble had assumed that the Large Magellanic Cloud was at a distance of 0.034 Mega Parsecs. (refer Table 1 of PNAS Vol 15, 1929 pg 169). Based on the light echo from SN1987a, the distance of the Large Magellanic Cloud is less than 5000 light years. (refer An Alternate View of SN1987A)

Energy Conservation
We know that if you throw a ball upwards, it will slow down. As potential energy increases due to galaxies moving away from us, their velocity referenced to ours must decrease. But Hubble's states otherwise.