No one yet knows exactly what the BIG BANG was. It lies outside our best current models. No one knows if time existed before such a bang. No one knows exactly what caused the big bang.
And there are different ideas about what existed before such a bang, if anything. No one knows if there was a single big bang, multiple big bangs, or simply a series of repeated finite bangs. The standard model of cosmology used in these forums is the Lambda CDM model which applies observed parameters to the more general FLRW cosmological model, and these start after the big bang. They do not explain the initial bang itself.
It is believed everything we currently observe around us, all the particles and different energies, for example, like gravity, the strong force, the electromagnetic force, maybe time and space, originated from such an initial high energy and unstable beginning in what is called spontaneous symmetry breaking.
Many of the core ideas of the Big Bang, like the expansion, the early hot state, the formation of helium, and the formation of galaxies, are derived from and confirmed by observations that are independent of any cosmological model.
So we know our models fit what we observe pretty well because we made them that way; whether they are the final solution remains an open question. The cosmological models, theories of the very large, are based on Einstein's General Relativity; It may be more likely that what caused the big bang will eventually emerge as a result of the theory of the very small, related more closely to quantum theory. Stay tuned!
...later on :zzz:. Later on. I ended up showing them a program on NOVA by Neil, TTWH by Freeman, BBC's and few other stuff. It has blinding colors (HD), CGi, cool allegoric animations and annoying explosions which they kept on repeating. Some of the part are misleading. I just can't figure out if it was done on purpose or for entertainment's sake. 
