This thread properly belongs in philosophy. Hopefully it will be moved there, because I am planning to now philosophically expound.

The determinism being spoken of here is best summed by the following quote from Pierre-Simon Laplace;

"We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes."

—Pierre Simon Laplace

Such a view is unsurprising considering that Laplace lived in the age of Classical Newtonian Mechanics. before Einstein and Relativity, Quantum Mechanics, even before Maxwell's Equations.

Here is the Wiki on Laplace;

Pierre-Simon Laplace - Wikipedia, the free encyclopedia

Of course, if one wishes to maintain a biological view of human consciousness, without resorting to metaphysics, then it follows that free will is wholly illusory if absolute determinism is true.

To paraphrase, in a context of scientific materialism, determinism and free will are mutually exclusive.

Now let's look at Quantum Mechanics, which as it now stands predicts probabilities while offering no definite outcomes. Einstein was of the opinion that quantum particles did in-fact obey deterministic rules but that there were variables unknown to quantum theory.

However there was a physicist named John Stewart Bell who provided a theory that makes a very strong case for Quantum Mechanics as truly stochastic.

Here's the Wiki on it;

Bell's theorem - Wikipedia, the free encyclopedia

It would appear that the basic building blocks of all matter do not behave completely deterministically.

Now let's consider Big Bang Theory. While BBT doesn't directly address the initial moment of the BB it does get within about 10^-40 second or so of it.

What BBT does unambiguously state is that it wasn't an expansion of matter into a preexisting space and time, but it was an expansion of matter, space, and time itself.

Since there is no discernable cause preceding the BB there can be no assumption of determinism in the origin of The Universe.

There is one more piece I need to show before I stitch this all together.

Check out The Law of Large Numbers;

Law of large numbers - Wikipedia, the free encyclopedia
Considering the probabilistic nature of QM, and a potentially causeless origin for The Universe, I propose that determinism cannot be axiomatic.

Axiom - Wikipedia, the free encyclopedia
Determinism is instead an emergent property from probability according to the law of large numbers.

Emergence - Wikipedia, the free encyclopedia
Within the context of causality being emergent as opposed to axiomatic we now have some wiggle room to entertain various hypothesis concerning free will as true, without resorting to assumptions of metaphysics.

Just some of my thoughts. Thank you for your consideration.