What is the Big Bang?
It is the ineffable explosion that, according to some, created the first sub-atomic particle (matter and energy). With that explosion, space and time came to being too; there was nothingness before the Big Bang.
Arguments for the Big Bang
Firstly, in 1814 William Wallaston launched spectroscopy. He showed the dark lines that separated the spectrum of the sun. Later in 1850, German physicist’s Gustav Kirchhoff and Robert Bunsen started spectroscopy for individual elements. William Huggins in 1863, managed to observe some nearby stars with a refractor that had a spectrometer attached to it. He was able to link Bunsen and Kirchhoff’s spectrum lines from different elements to the ones observed on different stars.
An Austrian scientist, Christian Doppler, had observed something taking sound waves into consideration, 20 years ago. He noticed that the frequency of sound waves changes when they travel from the source to the observer. The pitch decreases when they move away from the observer. Doppler believed this was true for light waves as well but it was proved later by some French physicist.
William Huggins observed the spectrum lines of hydrogen on Sirius shift towards the red end of the spectrum. This indicated that Sirius was moving away from us.
Hubble took into consideration the star Cepheid, the one that fluctuates in intensity and he successful in finding a galaxy other than the Milky Way. Using Vesto Slipher‘s idea of finding radial velocities, Hubble concluded that the increase in radial velocities could show how far the thing is. The radial velocities would keep increasing for the stars in the other galaxy and the redshift was so intense that the spectrum lines would change colour at that end.
The universe was definitely expanding.
He proposed a cosmological theory that explained a universe expanding infinitely and after this was brought to light it brought a few other papers to light that were written ten years ago by a Russian mathematician, Aleksander Friedmann.
Friedmann gave three possible models of the cosmos. If the matter in the universe is greater than its critical density, the universe will collapse. But if the critical density is more than the matter the universe will expand forever. The third model is that if the universe is flat with a constant zero at critical density, then again it would expand infinitely.
Now the question of the origin of the expansion came to notice and Lemaître came up with an answer. He took into consideration the second law of thermodynamics and made an assumption of the expansion as increase in disorder. Accordingly, the increase in entropy can be justified too by the explosion of a nucleus.
George Gamow added that the nucleus alone could not account for that temperature and chaos, the nucleus with protons and electrons can. Hence, the singularity would be an atom and not a nucleus.
So they universe is definitely expanding at the expansion has to have an origin. The origin is the Big Bang. There is no reason to believe in it, it’s just another theory. God could still be the primary mover and he might have started the big bang, planned it perfectly well and thought of all the consequences.
God could be a child playing in his lawn too. He planned a rocket launch in his lawn with his toys that were made of nothingness perhaps and something went wrong, which made the Big Bang. So whatever happened after the Big Bang was not planned at all, we just came out to randomly exist and yet there still was a prime mover.
This content is from my Philosophy of Science class (Spring 2012). We had quite an elaborate discussion on this subject.