click to enlarge
In 1842 an Austrian physicist, Christian Doppler proposed an
hypothesis about the possible change in frequency of a wave in relation to an
observer who is moving with respect to the source of wave. Doppler expressed his views in his thesis titled:
On the coloured light of the double stars and certain other stars of the heavens. During the presentation of his work he predicted the possibility of using this information for determining the distance and movement of stars from the Earth.
Later in 1915 Einstein proposed his General Theory of Relativity. Einstein added the cosmological constant to make the GTR match the current theory that the Universe was static. His initial thoughts were that it was dynamic and either expanding or contracting. Later, with Hubble's work in 1929 it was shown to be expanding, and Einstein claimed the cosmological constant his greatest blunder! It was Georges Lemaître in 1927 who first made this expanding Universe hypothesis in his big bang model, but Hubble expressed it in empirical form:
V = H0D
Where V is the recessional velocity, H0 is the Hubble constant, which is the numerical value of rate of expansion of the Universe, and D, which is the distance of the galaxy from Earth.
The difficulty in the accurate measurement of the value of Hubble constant was the biggest obstacle in the path of determining the age of the Universe. But in 1958 an American astronomer Allan Rex Sandage, successfully determined the value of the Hubble constant and proposed the age of the Universe to be somewhere between 11–15 billion years. But it wasn’t accepted due to the lack of physical evidence to back this proposal; however this led to more research.
