The Big Bang is not an explosion of matter moving outward to fill an empty universe. Instead, space itself expands with time everywhere and increases the physical distance between two comoving points.There are several issues with these claims...
Foremost of the issues is that the Big Bang doesn't even CLAIM to be a creation event (nor an 'explosion'), it is an expansion - often characterized by an Inflationary period that evidence suggests began within those early moments.
The Big Bang theory CANNOT address events prior to about 1 Planck second because we have NO direct or indirect knowledge of that period. So these assertions are just grossly and plainly false.
So I want to be very clear - when creationists make these claims they are 'BEARING FALSE WITNESS'. Furthermore, when they are making these claims publically they have purposefully abandoned their duty of due diligence. In my book this makes you a LIAR. Not merely mistaken, a flat out LIAR. There is no excuse for purposefully misrepresenting science. You Are A Liar. Period.
Now, if you have any Intellectual Honesty (even that of the size of a grain of mustard seed), you will admit your error and work to correct it. If you don't do this then I find you not only a Liar but a Fraud in my book. And if you are stuck at this stage in your intellectual development you might as well stop here.
Before we move on let's also clear the air about this word, 'Theory'. If you look up the definitions of the word 'SET' you will find on the order of 464 DIFFERENT definitions. How can a word with 464 definitions even be useful, how would you EVER know what was meant when "you were all set to set the cup on the tv set"? Simple, we interpret the term based on our knowledge of the context.
There are only about 12 definitions for the word 'theory', but we only really care about TWO of them:
(1) Scientific Theory: a well-substantiated explanation of some aspect of the natural world, based on a body of knowledge that has been repeatedly confirmed through observation and experiment
(2) theory, colloquial: a hypothesis or guess about something
Scientists and educated people have no problem, "working on a test of String theory to see if we can demonstrate it as a Theory". The first usage is informal, the second is formal in the scientific sense of the term. So, 'String theory' is NOT a Theory of science, it's not even a proper hypothesis. It is, at present, only a mathematical framework that may or may not correlate to physical reality. Someday, some formulation of this 'theory' might become a proper hypothesis and eventually be confirmed as a Scientific Theory, but that isn't the current state of things.
If you purposefully misuse this term to MISLEAD people (e.g., "Evolution is still just a theory") that is called an Equivocation. This is also called 'BEARING FALSE WITNESS' or LYING.
Back to the Big Bang... I will grant you that many 'popularized' accounts of the Big Bang misuse metaphorical language such as 'explosion' but that doesn't align to the Scientific Theory of the Big Bang as published in reputable, peer-reviewed journals. It is just that, metaphorical language.
One of the fundamental laws of nature that we have been able to infer (over about 22 orders of magnitude) is that matter-energy are neither created nor destroyed. So the logical inference drawn if this law holds is that matter-energy we know today was not created in the Big Bang. In fact, the typically envisioned scenario is explained as "everything was compressed into an infinitesimally small point". This is not at all the same situation as all of the stuff of the universe magically coming into existence out of nothing.
What we have before that first Planck second is an UNKNOWN. There is absolutely NO evidence for what happened before that moment and very little data to guide us. We can, at present, only make inferences that GREATLY EXTRAPOLATE beyond our current theories but they are merely GUESSES. When such a 'guess' can be formulated it in a way that it can be tested (falsified) AND it accounts for all the known data and isn't contradicted by any evidence then it can be called a Scientific Hypothesis. We are, at present, not at the stage of having any Hypotheses about what happened BEFORE the Big Bang.
Unknown does NOT equal God.
There are several working frameworks in which the possible origins of the Big Bang are explored. The most popular of these are known as 'String theory', 'M-brane theory', and Quantum Loop Gravity (hints of pre-Big Bang fingerprints). In some of these, the CAUSE of the Big Bang are Quantum Fluctuations out of a kind of 'Nothingness' that we cannot describe and we have no scientific guidance on currently (but one piece of evidence in favor of this is that our Universe appears to consist of Zero Energy as a net sum). There is also the Hawking-Hartle model in which the origin event doesn't exist in time and is thus unbounded (there is, mathematically speaking, no 'beginning'). There are also theories (again, in the colloquial sense) that our Universe is merely one in a vast sea of a multiverse.
It is, in fact, the creationists who believe in a creation ex nihilo (out of nothing)... First, these bastions of skepticism, who (rightfully) demand evidence in every claim of science, suddenly become the gullible sheep when they appeal to their unevidenced god-concept as the creator and they hand-wave an appeal to the unevidenced 'transcendent' for their eternally existing god. I could just easily appeal to a transcendent mote which is ever-existing and spins out universes. How does it do this? Oh no! You aren't allowed to ask that question, it JUST DOES. What does it create these universes out of? It JUST DOES. Why doesn't it require a creator? It JUST EXISTS, it's transcendent silly, you can't even ask this! And the 'magic' that has REALLY been done here to utterly squelch legitimate inquiry.
Oh no, they say, it MUST be, not just a god, but MY God. And more often by a wide margin, The God I just happened to be inculcated with through cultural experience. And when it's a Muslim isn't it such a pity those billions of Christians just have it wrong? And when it's a Christian, the other way around.
If our scientific understanding of the conservation 'Laws' are wrong, and matter-energy CAN be created/destroyed by some process then it becomes even more difficult to say anything based on the science, which you are depending upon in your premise - so the premise fails on this front as well.
[This is a DRAFT - Work In Progress]