Big Bang

The Big Bang Theory

At this moment in time the most popular theory for the creation of our universe as we know it is the “Big Bang Theory” which is estimated to have occurred 13.72(±0.12) billion years ago1. There is much evidence to support this theory however it also posses some problems.

Evidence For the Big Bang

The first piece of evidence for the big bang I will be discussing is the observed red shift of the electromagnetic radiation of stars and galaxies. This effect was first noted by American physicist Edwin Hubble circa 1919 and in 1929 he published his findings2. His research had shown that the spectra of the light from distant light sources shift towards the red end of the electromagnetic spectrum3. The result of this is shown to the right. The two spectra compare the absorption lines of distant galaxies to the right with that of the Sun on the left. There is an obvious increase in the wavelengths expected from the distance source.

The reason for the increase in wavelength of the electromagnetic radiation from a distance is source is that the universe is expanding. This means that it appears that stars, galaxies and nebulæ are moving away. The extent of the red shift of a source can be found by using the formula below:


Where z is the red shift ratio, λ0 is the expected wavelength without considering the effect of red shift and where λ is the observed wavelength.

Hubble postulated that there is a linear relationship between the recessional velocity, v, and its distance, d, i.e. [pic]. To write this in the form of a formula we must include Hubble’s constant, H0:


The units of v, H0 and d, are km-1, km-1·Mpc -1 and Mpc respectively.

The graph overleaf shows recessional velocity against the observed body from the observer.


Using this formula we can also approximate the age of the universe as we know that [pic] and since [pic] then [pic]. However, this will only give an approximation of the universe’s age...