Science doesn't "prove" that everything is entirely deterministic, it approximates the universe as deterministic by way of methodology.
Determinism, as a concept, is incoherent because to hold it must hold invariably down to the minutest detail. If there is any freedom within the system, then we can know that determinism is false. The issue here is those denying "free will" are making unnatural distinctions and playing a shell game that makes it unclear what it is they are actually denying since they seem to admit that we have both freedom and intention. So the entire "argument" is muddled, because we have determinism being asserted without support for that assertion and then a consequence of determinism being affirmed. If the determinists would clarify what the missing element for free will is that they deny, perhaps we could have productive discussion since we could see if it truly is necessary or if there is cause to deny it.
Science can clearly show and prove, beyond any sense of reasonable or rational doubt or denial, that these atoms or molecules, or mass of stuff, is moving along at this or that trajectory (and velocity/speed/temperature/environment) and then runs into or interacts with this or that mass of stuff, and then produces this or that effect after interacting with this or that mass of stuff, which then goes on it's way to then interact with more stuff, etc, etc, etc, and such and such, and so on and so forth, etc. Anyway, all of that can be shown way, way beyond any kind of rational or reasonable doubt to always be deterministic always, etc, and it never does anything different, or ever acts/reacts/behaves in any other kind of other way ever, and I mean like "ever", etc, and there is no denying that ever, because it is 100% solid and unchangeable "fact", etc. And since both we, and everything else, is all made up of all of that stuff, then there is no way that our actions/choices/decisions/thoughts/interactions cannot be anything other than deterministic always also, since we are all, all of us (and everything else) is all just made up of, and is all just extensions of all of that stuff, etc. It's really quite simple really, etc. So simple in fact, that I just 100% absolutely cannot believe that you guys cannot see it, or won't admit to it, etc.
And also, theologically speaking, it is also the one and only way any being can be fully omniscient always also, etc. And I also cannot believe you guys cannot see or admit to that also, etc. Even although that is not my primary reason for thinking determinism is 100% truth, etc, but is more due to other reasons that I have just now mentioned or stated earlier, etc.
God Bless.