The Big Bang a unproved conjecture happened 13.8 Billions years ago, assuming that it really happened, Big Bang started from singularity which arises from using Einstein’s equations for gravity. Its very very long time ago, many things or process might have happened and they don't exits now .The only resources we have to find what happened 13.8 Billions back are the telescope however sensitive it may be and the light (electromagnetic waves) . These tools may not be enough to predict what happened since Big Bang. To correctly predict all the events that have happened right from the Big Bang we need to have all or most of the recordings of all the events which is almost impossible.
Whether why matter dominated the antimatter or who turned on the Higgs field to give the mass to the particles are very difficult or almost impossible to predict.
Many more questions remained unanswered ,what was there before Big Bang, what caused Big Bang and do we have single universe or multi-universe. The dark matter and dark energy still a mystery . Finally how universe is going to end in a big crunch or ripped apart because of endless expansion.
We are still in search of a single theory often referred to "theory of everything" which can combine both Einstein general theory of relativity which applies to large structures of universe and the quantum theory which applies to subatomic particles. A single theory which unifies all the fundamental forces of universe. I mean quantum gravity .
The most important fact is that many process are difficult to replicate in laboratory. But scientific endeavor continues.
