Truth is, scientist don't even know that the big bang happened.
It is just the best theory they have for the Orgin of our universe other than 'in the beginning God".
Some scientist even believe that before the big bang there was absolutely nothing, and that the big bang literally created everything (both matter, and all the laws of Physics and Time) from nothing. The problem is that they don't really have that much proof for it other than that the galexys seem to be moving away from each other for some reason.
There are also many countless other problems with the theory such as how we got all of the elements on the periodic table from just hydrogen. Some scientist have tried to say that fusion (happens in stars) can explain this, but the problem with that is you can't fuse new elements past Iron.
Another problem with is is that the big bang theory defys the law of entropy (2nd law of therodynamics) which states that the universe, and everything in it naturally tends towards chaos, and that order cannot arise on it's own from chaos unless thier is an inteligent system or creature to harnass that energy. Raw energy alone (like with the big bang) can only destroy things (just like how the sun causes erosion, or the energy from an atomic bomb is destructive). To have order, you need a organism/system such as a plant to harness the energy (like sunlight) and use it to create order.
Scientist are still unsure how an explosion that they think happened billions of years ago could have possibly created the immensely orderly systems such as solar systems and even galaxys that we see today.
