Evidence of Big Bang

 

Brief Informal Student Forum (Part II)

lim ju boo 

University of Oxford

2018

What evidence is there for the Big Bang?

In cosmology there are two schools of thoughts on the origin of the Universe

The first one has only a minority of support and is based on a steady state model in that the Universe is always there, and the same whereby the density of matter in an expanding universe remains unchanged due to the continuous creation of matter.

However we now have more empirical evidence in favour of the Big Bang theory. Three major evidences are:  

1.        Red-shifts Spectra:

Edward Hubble in 1927 was able to determine the distances of Cepheid variables by observing their luminosities varying with their periodicities; the more luminous the Cepheid, the slower the variations, and by using the fact that the intensity of light varies inversely as the square of its distance, he was able to establish their distances

Later he was able to demonstrate even further the distances to the galaxies by observing their spectra.  He showed the galaxies were actually receding from each other with no central point in the inflation. He observed their spectra were all red-shifted with increasing velocities with increasing distances.

This was the first clue that the Universe is actually expanding away towards a finite edge (Observable Universe) - the further away the galaxies, the faster the velocity of recession.

The rate of expansion was determined at a rate of about 21.5 km/s, small though, but over time of 13.7 billion years as the age of the Universe this is significant in terms of the distance it has expanded. This expansion can only be the result of a Big Bang.

2.        Cosmic Microwave Background (CMB):

Perhaps the best evidence that the Universe started off with a Big Bang from a super-dense singularity is the presence of an almost uniformly distributed CMB with regions of small variations here and there in the temperature spectrum.

The CMB is manifested as an afterglow which is the heat remnant of a Big Bang.  The CMB afterglow is just 2.7 Kelvin above absolute zero, and seems brightest at wavelength around 2 mm

The CMB radiation discovered in 1964 provided the crucial evidence of a Big Bang model. The universe in the mini seconds after the Big Bang was hot, dense, and opaque plasma

Georges Lemaitre first noted in 1927 that an expanding universe could be traced back in time to have originated from a single point on which scientists have built a cosmic expansion based on his idea.

3.       Nucleosynthesis of Elements:

Tllar nucleosynthesis by neutron capture.

Thhe Sun and stars convert the most abundant element in the Universe - hydrogen, into helium through fusion energy. As energy is released, the higher ratio of hydrogen to helium is being shifted towards helium.   

In the main sequence stars other elements heavier than iron are also being formed through stee abundance of other elements other than hydrogen and helium seem to suggest the cooling effect after a Big Bang when  particles like protons, neutrons and electrons can come together to form elements

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