Although I am a determinist myself, there are some misconceptions about free will and predictability.
Quantum Physics (a set of the most successful theories out there) suggests that our Universe is not ABSOLUTELY, but only partially, predictable. If you have a particle P that is in a superposition of states (which means that it can have spin-up and spin-down at the same time), then we measure its spin: the superposition will be destroyed and the particle will take spin-up or spin-down (and not both). And there is nothing in modern physics that can predict what spin it will take, and physicists only talk about the probability of measuring spin-up or spin-down (like 80% spin-up and 20% spin-down)..etc.
So, fundamentally speaking, the Universe is unpredictable in essence. If we turn the clock back to 7 million years ago, nothing in the Universe guarantees that humans will evolve, there is evidence that goes against physical determinism, in this sense.
Philosophical determinism on the other hand (that we have no free will) is essentially different. Although nothing is totally predictable in the Universe, this does not necessarily mean that we have free will (since we do not have control over the quantum world, or whether particles measure spin-up or spin-down), as it turns out : we, too, submit to the unpredictability of the quantum world, regardless of our own free will.
Suppose that a murderer has no free will : the act of murder is a result of what happens in the brain, sets of neurons fire as a result of different stimuli, which is a direct result of what happens in the quantum world, where particles assume different unpredictable values for their different features (like spin, an electron in this neuron decided to take spin-up, another electron took spin-down ...etc), and all these quantum phenomena are physically non-deterministic (physical determinism is false), although the murderer himself does not have any control over it (philosophical determinism maybe true, remember : this is philosophy, so maybe ).
As you can see from the previous example, we can conclude 4 conditionals :
PREDICTABLE : You can absolutely and totally predict what will happen in the system, in principle. That is: Physical determinism is true.
FREE WILL : Philosophical determinism is false.
- If PREDICTABLE then NO_FREE_WILL
- If FREE_WILL then NOT_PREDICTABLE
Those are true premises I guess, simply because if physical determinism is true then it is necessarily the case that we can never do something that is independent of the physical world : We did it because the physics says so.
So, if the whole Universe is predictable in principle, then no free will. This answers your question.
I add that, there are 2 false premises (in my opinion):
- If NO_FREE_WILL then PREDICTABLE
- If NOT_PREDICTABLE then FREE_WILL
These two are equivalent premises, but they are false premises.
If you have no free will (like the murderer in the previous example), it does not necessarily mean that you are 100% predictable. Because your brain is also subject to quantum phenomena that are themselves unpredictable.
Note : As I am no compatibilist, I did not talk about that position.