Do We Actually Choose?
When you said no today, did you decide that, or was it closer to a coin toss?
The central question: are we the source of our choices?
Everything else in this debate branches off that one.
The classical case for determinism
If you knew where every particle started, you could predict everything after it. Your decisions follow from your experiences, those follow from earlier experiences, and the chain runs back to the Big Bang. By that logic, your "no" was settled 13.8 billion years ago.
Quantum mechanics shakes that
Experiments testing Bell's inequalities earned Aspect, Clauser and Zeilinger the 2022 Nobel Prize, and they rule out local hidden variables.1 Some interpretations, like Bohmian mechanics and many-worlds, stay deterministic, so the physics doesn't strictly disprove determinism. See the Nobel press release. In standard quantum theory, single outcomes are probabilistic, so the first instant doesn't obviously fix every particle's path.
A coin toss doesn't decide anything, though.
Randomness gives you outcomes, and a decision needs reasons behind it.
If my choice were pure quantum noise, it wouldn't be mine either. Free will needs a mind that weighs reasons, reflects on its values, and acts on them.
Overlapping sets
Compatibilists say free will means acting on your own reasons without coercion, which holds whether the physics is deterministic or probabilistic.1 The two ideas overlap, so free will doesn't have to defeat determinism first. [^2]
What about the brain?
Libet's 1983 experiment suggested your brain "decides" before you're aware of it. Schurger, Sitt and Dehaene (2012, PNAS) found that the readiness potential may be background neural noise that crosses a threshold when you act.
In their model, the signal doesn't show the choice was already made. 2 This post was written using Artificial Intelligence for testing purposes.
So, does free will exist?
The evidence can't settle it. It does suggest the universe wasn't a script written in its first second, and that choices grounded in your own reasons are yours.