What are some physics-based arguments against hard determinism?

The definition of "free" and "will" are to shady to be scientific.
So there is no scientific arguing about it, just philosophical.
- I like this take, but it also makes me feel like I could do a better job describing the intent of my question in more scientific terms. I hope to do so, here.
  If one were to have sufficiently advanced technology akin to future MRI machines that could image the state of the human brain at Planck time resolution, my argument is that the very process of "a decision" (act, choice, idea, etc.) could be quantified. And if that is the case, then there must be chemical triggers and causal events that could have predicted that state of the matter and energy. And if that's the case, then we must really be products of our environment in an (currently) incomprehensibly large chemistry equation.
  If any one decision could be quantized, reverse engineered, and then predicted through such means, then it stands to reason every decision can be. And if that's the case, free will cannot exist.
  
  I agree with the other poster that you need to define what you even mean when you say free will. IMO, strict determinism is not incompatible with free will. It only provides the mechanism. I posted this in another thread where this came up:
  The implications of quantum mechanics just reframes what it means to not have free will.
  In classical physics, given the exact same setup you make the exact same choice every time.
  In Quantum mechanics, given the same exact setup, you make the same choice some percentage of the time.
  One is you being an automaton while the other is you being a flipped coin. Neither of those really feel like free will.
  Except.
  We are looking at this through an implied assumption that the brain is some mechanism, separate from "us", which we are forced to think "through". That the mechanisms of the brain are somehow distorting or restricting what the underlying self can do.
  But there is no deeper "self". We are the brain. We are the chemical cascade bouncing around through the neurons. We are the kinetic billiard balls of classical physics and the probability curves of quantum mechanics. It doesn't matter if the universe is deterministic and we would always have the same response to the same input or if it's statistical and we just have a baked "likelihood" of that response.
  The way we respond or the biases that inform that likelihood is still us making a choice, because we are that underlying mechanism. Whether it's deterministic or not it's just an implementation detail of free will, not a counterargument.
  
  Now here’s an interesting take.
  In principle, one might be able to predict behavior based on this model.
  But I would asset that it is not possible to achieve these conditions no matter what godlike technology one has.
  Let’s go simpler. We don’t want to predict a human we want to predict the path of one electron.
  Starting from initial conditions we should be able to predict the path of that electron right Wrong!
  It’s wrong because it is impossible, in a way that cannot be overcome in this or any universe, to know those initial conditions.
  And that may seem like a technicality, but that’s exactly where the removed in the armor is: no matter how precise your model, it’s impossible to determine the state of a closed system, because it’s closed, and it’s impossible to predict the behavior of an open system, because its evolution is determined by its interactions with its surroundings, and you can’t get all that information.
  So the idea of using physics to predict things precisely is a Platonic ideal, not a thing which can manifest in reality.
  
  The brain as far as we know works like nowadays "ai" it makes assumptions and tries to get the best and most fitting outcome for itself, this decision is influenced by a astronomical amount of data (thats the difference to nowadays ai) and (for the lack of better scientific measurements) emotions, meaning that theoretically it is possible to perfectly predict your choices, however, if you know about said prediction it will influence the system again.
  Saying you have to pick between a Red and a Green Gummy Bear with the exact same taste, you will probably pick the red one because the subconscious associates red usually with food (red and yellow, that's btw why many fast food chains use those colors) however, if you are aware of this, this will likely end up in picking the green one as rebellious act against nature, wich again is predictable because humans are self aware and don't want "to be slave to their own instincts" now if you know about the prediction, the only way to "be unpredictable" would be to not chose a Gummy Bear thus "breaking" the test... Wich is predictable. This is of course a very simplistic experiment but gets the point across, you can't be unpredictable unless you break the laws of physics. This does however not prove or disprove the "free will" inside the system you are in, you could chose things freely, you just don't because its unnecessary and time consuming.
  TLDR: we don't know.
  
  I believe your scenario conflicts with Heisenberg's uncertainty principle. As far as I know it's one of the most ironclad laws of physics. As a quote I found in Wikipedia puts it,
  The uncertainty principle actually states a fundamental property of quantum systems and is not a statement about the observational success of current technology.

I have a theoretical degree in nuclear physics, and it seems to me that sub-atomic scale events like quantum tunneling suggest that reality is neither fully determined nor fully chaotic, but something in between: probabilistic. Whether we can consciously affect the probabilities of our own actions remains an open question, but we can at least say that causality is not the whole picture.
- Do you have a degree in theoretical physics, or do you theoretical have a degree. ;)
  
  I'm a theoretical theoretical physicist. That's double the theory.
  
  Go back to work, Fantastic, you have a power plant to run.

One argument that might be made is that inconsistencies at the quantum level create an element of randomness that, while miniscule, could create massive cascading butterfly effects over the course of a large enough timespan. Whether those inconsistencies are enough to make more than a minimal difference in a single given lifespan is debatable at best, and the entire idea could be debunked if quantum physics was proven to be deterministic.
However, as it stands, we don't have accurate methods of predicting quantum behavior.

While quantum mechanics certainly gives random jumps, by no means is anything in control of those random processes (otherwise, they wouldn't be random)
So, even though the universe may not be fundamentally deterministic, that doesn't mean free will exists

Free will can be defined as:
A state of existence in which one’s decisions are a predictor of one’s actions.
I don’t see where that conflicts with determinism, honestly. It’s two different levels of analysis.
If you define free will as, by definition, something that breaks the laws of physics, then free will, by definition, does not exist.
Kinda like when someone defines “magic” the same way. If “magic” is by definition something impossible, then by definition it doesn’t exist.
The questions get a lot more interesting when you define these things in a way that doesn’t make them, by definition, non-existent.
Maybe this type of reasoning should be called Trivial Dismissal.
Another example. If you define God as a man in the sky who controls everything, you’re not really an intellectual tour de force if you conclude he doesn’t exist. It’s the more interesting definitions of God that lead to more interesting discussion of whether God exists.
- That seems to me like an entirely inadequate description of free will, because the interesting question isn't how decisions lead to actions, but where the decisions themselves come from, i.e. whether the decisions are made freely. Unfortunately I've yet to see any definition of free will that doesn't rely on hand-waving the definition of words like "free" or "could". We have intuition about what those words mean, but they don't appear to have any rigorous definition that applies in the context of defining free will.

- You don't need a hidden variable for determinism though. Multiple worlds theory has no hidden variables but also no non-deterministic processes.

Free will is tricky, but there's interpretations of quantum mechanics that aren't deterministic. (Although multiple worlds QM is deterministic!)
That's it. Everything else in physics supports determinism. The fundamental physics so far even conserves information/can be traced (CP-inverted) backwards.
- CP symmetry has been experimentally measured to be violated. What we still believe is that our world is invariant under CPT symmetry.
  
  Yes. As I understand it, to preserve CPT during a T violation, you have to invert (break) CP, but it can be done.
  So, you could theoretically make a kaon plasma with weird unidirectional (and so T-violating) non-thermodynamic behavior if you had a strong enough box, but in the process it would inevitably accumulate handedness and electric charge in a way that preserves information.
- Yeah, when writing this I sort of had the notion that any argument against hard determinism using quantum mechanics would instead 1) actually prove multiverse theory, and 2) therefore still prove in favor of determinism.
  
  Quantum Mechanics' hard indeterminism doesn't prove the multiverse interpretation, it's just one of several potential explanations for the randomness we see.

This is the best thing I’ve seen on Lemmy so far. Physics based philosophy, hell yes.

Also not very educated on this, but just throwing out what i thought was the outline here:
Tiny differences in position or speed can lead to drastically different outcomes https://en.m.wikipedia.org/wiki/Chaos_theory
We can only know position or speed https://en.m.wikipedia.org/wiki/Uncertainty_principle Thus, predicting the future cannot reach 100% accuracy.
If this means that we might have free will i cant say, but if the world is wholly deterministic, the above at least underlines our lack of ability to predict it.
Regarding god of the gaps, annoyingly, the claim here is actually that we ”know” that we cant know:
”Thus, the uncertainty principle actually states a fundamental property of quantum systems and is not a statement about the observational success of current technology.”
Of course, only until falsified - field is always changing: https://www.scientificamerican.com/article/common-interpretation-of-heisenbergs-uncertainty-principle-is-proven-false/

carefully leaves his philosophical hard determinism at the door.
Well, I'd better learn a thing or two
- One of the highest-level, most abstracted arguments against the idea of humans as deterministic goes like this:
  When you treat people as if they’re automatons, they really don’t like it. And societies that don’t model people as having free will tend not to do so well.
  
  I'm trying to patch together my conception of free will and determinism to sum it up here in answer, but it's full of holes. Basically it goes like this. Determinism is the rule of nature and, of course, mankind. Free will doesn't exist. Some measure of freedom and emancipation, on the other hand, do exist. It's hard to sum it up. Basically, very close to a spinozist stance, just with more holes and gaps. But I'll stop here since the OP specifically asked to leave philosophical perspectives at the door.
  
  That's a good argument. It reminds me of the idea of free will as a necessary illusion. Something that us fundamentally not true, but without which societies can't operate.

Slightly off topic, but the god-of-the-gaps has plenty of space in maths alone. The Incompleteness theorem by Goedel shows that in any mathematical system there will be unprovable truths.
I have no idea how to map that onto free will.
- Yeah, I've thought about this a little bit but again my math isn't so strong.
  I guess approaching this more from computer science (something I'm more familiar with) you could compare with stuff like the NP Hard class of problems. And thus I offer that unproveable does not mean "wrong". We generally "know" that P=NP is wrong but we cannot prove it only because we lack omniscience. Us lacking the information (in the physics sense of the word i.e. Hawking radiation) doesn't mean the information isn't there to be quantified.

All I know is that this post makes me want to watch Devs again. OP, if you haven't seen it, check it out - one season miniseries about exactly this
- Ohh thank you! Is missed this one - looking forward to it
- Thanks for this recommendation. I'm going to have to watch it.
- I'll have to check it out

The double-rod pendulum is one of the simplest dynamical systems with chaotic solutions. ...from Wikipedia
This system is very simple yet even with initial conditions varying by (less than) Planck's time or Planck's length, theoretical resulting behavior changes after a few cycle.
Physical determinism says that there cannot be creation of (new) information yet this system does exactly that.
- Also it should be pointed out that this doesn’t require indeterminacy to happen. A perfectly deterministic Newtonian model of the double pendulum will exhibit the chaotic behavior.
  It’s almost like if you put a black box around that pendulum, on which a light blinked each time the two pendula were parallel (ie when their joint was straight), the blinking of that light would seem “probabilistic”.
  And it would be unpredictable too. Despite a perfect, zero-fuzziness Newtonian model determining the pendulum’s behavior, it would be impossible to predict the blinking of the light.
  I’ve only had the briefest introductions to chaos theory but it’s fascinating.
  
  And it would be unpredictable too. Despite a perfect, zero-fuzziness Newtonian model determining the pendulum’s behavior, it would be impossible to predict the blinking of the light.
  Wait really? How?
  
  Hi @intensely_human
  You are the only one here who gets it easily even though I didn't say much. Also in this tread I'm now up to 8 levels' comments with @grabyourmotherskeys but we are getting nowhere & I am quite feedup. So if you could do something here I would appreciate.
  Thanks
- Here's the thing. At what point does the causal chain get interrupted, free will kick in, and then the old causal chain fires back up? Because that's what arguments like yours are implying.
  The response is always that I don't understand the theory you have put forward. I'll grant that.
  If the proof free will is tied to a seemingly stochastic system how is that "free will". If I replaced your decision making with a random number generator would that be free will?
  I sincerely hope you will engage with me here.
  To be perfectly clear, my view is that we do not have free will but our limited set of information makes it seem like we do and so it is rational to continue on despite this. Put another way, I know the latest Mission Impossible movie was made months before I saw it, and that the outcome was predetermined, but wow, what a ride.
  
  I'm glad you're enjoying this topic as much as I am
  
  At what point does the causal chain get interrupted ( ... ?)
  The system is diverging at every point in time :
  In chaotic systems, the uncertainty in a forecast increases exponentially with elapsed time. (... same article from Wikipedia)
  I believe one has to see this before being able to apply it to free will explanations.

I'm far from knowledgeable about this, but the only thing I'm aware of that might disrupt determinism is quantum mechanics. Something about particles at that level not having set values until they are observed, making them truly random. I have no clue how that could lead to free will. We still have no control over it. It's more like they are the base that everything else is determined off of.
- It controls us, so the randomness has free will, and since the randomness is a part of us, we have free will

We know cause and effect exist in the universe. We can use this to gain control of a lot of things in our world: for instance, when I push the letter “A” on my touchscreen, the letter “A” appears on my screen due to these cause/effect systems we have set up.
However, we know that the universe is not entirely describable via cause and effect. Heisenberg’s Uncertainty Principle precludes us from fully observing all aspects of a quantum system, Gödel’s Incompleteness Theorem shows that our knowledge of the universe will always be incomplete, and Schrödinger's Cat shows us the absurdity of trying to make concrete claims about observed phenomena using probabilistic models.
If the universe was purely deterministic and we were theoretically able to gain all knowledge of it, there would not be free will. But this is not the universe we live in. The universe we live in is one where:
Probability exists, so we cannot fully predict the future state of events even with perfect knowledge (i.e. Schrödinger can never gain enough knowledge to predict whether the cat is alive or dead before opening the box, because the event is fully probabilistic.)
There are aspects of the universe we cannot fully observe, because by focusing on some aspects we must filter out others, so observation will never be fully reliable.
Regardless of how much we learn, there will always be knowledge we cannot fully categorize.
If events in the universe were fully deterministic, then free will would be an illusion, because everything could be traced to an earlier set of causes, and decisions would not actually exist. If events in the universe were random, free will would have no meaning, because decisions would be arbitrary.
But we live in a universe where things are not immutable, but things are not equally likely. I can roll a fair set of dice for randomness, or I can weight them to create an uneven probability, or I can select a number to eliminate probability altogether. And we all make decisions with limited observations using incomplete knowledge that will only have a partial effect to affect the probabilities of future events. And that means we shape events without controlling them, so all of our decisions have meaning. We can also tell objectively based on observations that some decisions are better than others, while at the same time conceding that no decision is 100% objectively right or wrong.
And that, my friend, is free will.

Sensitive dependence on initial conditions. Time is kind of an iterative equasion so we can predict something to an extent but because we don't no the initial conditions to an infinite degree there will always be chaos. That's where the freedom is. As in, it's both. There is deterministic (you didn't choose where you were born, your economic status) but with those initial conditions you can make choices etc.

The very concept of the Self, presumably the director of free will, in context, is under threat. Eastern philosophies has held this position for centuries - now science seems like the idea :
https://bigthink.com/the-well/eastern-philosophy-neuroscience-no-self/
I don’t suppose any of you meditate by any chance ?