A common definition.
Scientific determinism: since every event in nature has a cause or causes that account for its occurrence, and since human beings exist in nature, human acts and choices are as determined as anything else in the world.

In this definition it is implied there not an Alpha event that started it all.
Otherwise what would be the Pre-Alpha event that caused the Alpha event.

So you can't get an event that isn't the product of a previous event.
Therefore the universe must be infinite for any event to happen.

Hard for me to describe the ramifications of this train of thought.
Looking for insight on what if anything this means for Scientific Determinism.

So scientific determinism I believe requires a finite set to operate within.
If the universe is infinite in expanse then I do not see how anything could be predicted exactly.
It would take an intelligence beyond our ability to understand to calculate with infinity.

And remember predictions require numbers to quantify something.
The more quantifiers you have the more accurate.
Basically it's a math problem. Even today we cannot %100 accurately calculate the circumference of a circle given it's diameter.

But more importantly how does one belief affect how you get what you want in life vs the other.

If I may add a twist.
Let's say for example that the universe is a multiple choice exam.
For each situation you are given a finite set of choices and you can choose freely the one you want.
Is that free will? A limited number of choices?
The knowledge and experiences we have and the ones we remember at the time of the choice is a finite set so they represent the multiple choices.
So If I don't see an option (for whatever reason) I can't choose it even though it is there.

Only omnipotent beings have true free will. They have the knowledge and power to choose whatever they wish from all available choices even if the number of choices are infinite.
In conclusion if you have a limited number of choices that are a subset of the actual number of choices do you have free will?