VeganDE

Part 1: Free will

Laplace's demon is but a "thought experiment", you could make the assumption that it knows everything without even needing to measure it. In fact, it wouldn't even need to interact with our Universe. What it would need is to know its initial state (big bang or whatever) and extrapolate from it (using the right maths/rules) what the position of the stars are now without violating the speed of light. Note that "to know" is not the same as "to measure".

It might be that this demon can't exist, but that itself doesn't disprove determinism, it depends on what reason is given.

Let's assume for a moment that one of the non-deterministic quantum interpretations is correct and the collapse is random. I see some problems with this (I'll enumerate them for better reference):

P1) If it's "truely random" then it follows it cannot be controlled or predicted. This means you wouldn't be able to use "free will" or any external force to influence it, because that would make them no longer "truely random". Making the jump to assume that they are somehow "determined" by minds would be a claim with no evidence whatsoever. And in fact there have been experiments in this regard (people trying to consciously look into the double slit experiment to cause a tilting of the result) without finding any repeatable evidence showing the mental state of the observers influence the state of quantum particles.

Quantum mechanics exposes a gap in our capacity of knowledge, but to me, using this to explain consciousness and "free will" feels a bit like the "God of the gaps". As soon as we reach a point in science that reveals the limits of our capacity for knowledge, people have the tendency to want to use that to attribute spirituality to it, giving it properties that have not been proven with any level of reliable evidence.

P2) This doesn't solve the problem of determining whether animals have "agency". Quantum decoherence occurs also in their brains, and I see no reason as to why we should expect an animal to not trigger quantum collapse (even in the Von Neumann–Wigner interpretation) unless you somehow make the assumption that in order to be a conscious observer you need to be human, which seems to be kind of an arbitrary line not based in any scientific evidence I can gather.

This also leads to the famous "Schroedinger's cat". Many physicists agree that using a measuring device on a particle in superposition causes it to collapse, but because we can only perceive that collapse when we examine the results of the measuring, some actually believe the "superposition" of states also applies to the entire apparatus and even any animal inside of it... it's kind of ironic that the attempt of Schrödinger to display the absurdity of the situation with his thought experiment has led to many people to use it as an example even though that was completely the opposite of what he intended. However, I can tell you that when I studied this in the University we were given the argument that you cannot extrapolate quantum superposition to the macroscopic level. Thought I have no idea if this view has changed nowadays.

P3) Quantum mechanics applies to all matter, everywhere in the Universe. Not just inside our brain... so what causes quantum decoherence in particles that are at millions of light years from any conscious human entity? are each individual particle a "free will" agent? are there consciousness on things just because they experience quantum superposition? or are you implying that most of the universe is in superposition until a conscious observer looks at it? I guess this would be the Von Neumann–Wigner interpretation... sure, though this brings us back to how this is just an interpretation of it. Like you pointed out, there are also other interpretations that contradict that... and I'll talk next about the study you linked:

hidden variable theories have been deeply challenged by the findings for which three physicists were are awarded a nobel prize last year. Those basically proved that our universe is not locally real.

Here's an explanation by physicist Sabine Hossenfelder (widely considered a "free will denier" :P): https://www.youtube.com/watch?v=Wsjgtp9XZxo ...she doesn't seem to believe the results contradict her expectations.

This starts to become complex (if it wasn't already) since quantum mechanics reinterprets a lot what "observer" means and it's not exactly clear to me what the experiment implies (I majored in chemistry, not physics) ...but as far as I understand, even if the Universe couldn't be simultaneously "local" and "real" at the quantum level, it could still be "non-locally real", which is consistent with the quantum non-locality most physicists already assume.

I'm not convinced that the experiment is incompatible with hidden variable theories. But thanks for the interesting take.