As hard as I try I cannot fathom the: "If it's untestable, anything is possible - if anything is possible, nothing is possible - nothing is the simplest and therefore best explanation" argument.

Everything requires a reason (the Existence of a reason or cause - if its comprehensible and testable is a separate question) The fundamental question always go back to "why and how Existence at all". Of course we cannot make direct measurements regarding the origin of Existence - but we can certanly base our hypothesis and theories on our acumulated knowledge and daily, testable physics. The corect logic would therefore be to extend all the known and proven constants into the unknown (through symetries, conservation of energy, ..) - not to allow there every single possibility, specially illogical ones,. Or to put it simply: Only when You eliminate the logical, can You turn to the illogical.

Nothing conclusive from our past and currenty physical knowledge proves, that Creatio Ex Nihilo is an actual phenomenon or even that it is physically/logically possible. Most importantly - there is not one single complete idea (that I know of) that explains the mechanism, of how absolute Nothingness (Non-Existence) can spring forth anything else but further "Non-Existence". I don't need to stress out that there is even less talk about why this Non-Existence would produce or could even allow for just one single universe. If anything - if Non-Existence could produce our universe it could (and must of have) produced many - if not all physicaly/logical universes - if not even more, illogical ones. Seems to me, that if You want to talk about true Creatio ex hinilo - You must support the notion of a max. large multiverse: An Ultimate Ensemble (which is the totally opposite view most people wan't to prefer Creatio Ex Nihilo for - Occam can be tricky sometimes).

Sure, there are theories that promote the idea of the Big Bang "from nothing", but there is always "something", that causes the Big Bang and that "something" never gets explained, which only pushes the question to the origin of "that" cause. And it usually hangs as being a sort of First Cause, a "Something" in existence, which is by far a better option than Creatio Ex Nihilio. You can include causality, entropy and similar notions to any kind of "Something" - but never to Nihilo.

True Non-Existence, event though a concept we never experience in reality, is a beautifull thing, because it has only one, clear and strict meaning. Total absence of anything and all (spacetime included). If its not that - it's "something". Of course, if it''s not Creatio Ex Nihilo, then we have to assume a past eternity of some kind (be it Primus Movens or a cyclic/paralel model). Sure - past eternity brings out problems - but not as many as a single or multiple Creatio Ex Nihilo. But Past eternity is based on factual knowledge and observation - its an extension of what we know into the unknown, rather making up new types of logics and physics.

the best way I found is to use modal logic for such issues: Everything can (quite easily and reasonable) be put into 2 categories: Actually possible and potentially possible. Actually possible are known and proven possibilities (assuming hard determinism doesn't hold, but thats a separate question), I could go left or right - a car could pass my house or it could not, etc. Potentially possible are possibilities, that "might be possible". It might be possible to go faster than light, to alter all the physical constants we know, etc. But it's not proven to be possible (and of course, the possibility never happened that we know of).

We can quite easily and rationaly posit, that there are no physical proofs and explanations for Creatio Ex Nihilo while it the same time we know that conservation of energy, causality, etc.... are proven and real constants (and that in some physical models we can show how the Past Eternal models are consistent, logical and give observable predictions).

Creatio ex Nihilo with its non-existing logic and missing proof is surely a "possibily possible" scenario, while Past Eternity is (if combined with specific physical models) an "actually possible" scenario. The first one is clearly less possible and less logical and we must conclude, that the second model is more probable.

And I come back again: Why go against Occam and favor Creatio Ex Nihilo, when we have simpler and logical alternatives? It baffles me. I can only attribute that to personal biases and/or extremley narrowminded "horse blinders" approach, that simply cannot give a complete and objective picture. Yes - accepting Past eternity means opening a Pandoras box worth of possibilities - but keeping Your eyes shut is not good, objective science.

As long as we have logical options (however complex) they will always be more probable then illogical ones. Occam favours "real" options above "potential" options.

Does the Universe need a God? Maybe not - but God definetly needs a universe and a past eternal one guarantees Gods existence if God is "actually possible" (Posthuman- or otherwise).