I have the feeling most people cling to free will as a concept because not having free will raises questions if a “self” truly exists. However the existence of free will can be as scary if not more, since how could we define a “self” if it could freely do something not based on what defines it.

I think it’s more complicated than free will existing or not.

If you knew every single possible value about the universe at its start and had a perfectly accurate model of physics, you could theoretically predict/simulate everything that would ever happen. For practical reasons, though, that’s impossible, even ignoring weird quantum effects, for the simple reason that that is a lot of data points, more than any of us could reasonably keep track of- it’s like how, in sufficiently controlled conditions, a fair dice can roll the exact same number 100% of the time, but there are enough variables that are hard enough to control for in a normal situation that it’s basically random.

Similarly, if you knew everything about every human on Earth, you could theoretically predict exactly what any of them would do at any given moment. Of course, that’s just not practical- the body and brain are a machine that is constantly taking in input and adapting to it, so in order to perfectly predict someone’s thoughts and actions, you’d need to know every single detail of every single thing that has ever happened to them, no matter how small. Then, you’d need to account for the fact that they’re interacting with hundreds of other people, who are also constantly changing and adapting. It’s just not possible to predict or control a person for any reasonable length of time like that, because one tiny interaction could throw off the entire model.

Just look at current work with AI- our modern machine learning algorithms are much more well-understood and are trained in much more contained environments than any human mind, and yet we still need to manually reign them in and sift through the data to prevent them from going off the rails.

So, technically, I suppose free will doesn’t exist. For practical purposes, though, what we have is indistinguishable from free will, so there’s not much point getting riled up about it.

Well let’s start by examining the phrase “free will”

The term free has at least two different meanings in common language.

A) free as in beer ( free from cost) B) free as in speach (free from control)

Both of these could be broken down more (e.g. Monetary cost, entropic costs, mental cost and societal control, individual control, physical control… Etc)

Now, “will” is a bit more tricky. In this context we generally use it to mean “choice” However desire, and intention also get mentioned in the definitions.

1. desire
2. intention
3. choice

When commonly discussed I would say people tend to talk about B3(the ability to choose without external physical control)

I would argue 3 requires 2 which requires 1

So now we discuss B1 - are we free to pick our desires.

This I find to be interesting. We often see people desiring things which seem foolish. Foolish as is Unwise. What makes something foolish? Seems to me foolishness is caused by a lack of data and poor modeling.

At this point my phone battery is at 6% So I’ll cut my response short. I see no truly free will. I think our desires can be shaped over time via our input (previous choices) however we can’t roll a die and pick our desires.

I don’t think this is a bad thing. Just maybe not ideal but what is in this world?

Deterministic with no actual free will, but complex enough that we’ll never be able to tell the difference. Essentially, our choices may technically be predetermined but for all intents and purposes, they are indistinguishable from free will and can’t be predicted.

I’m fairly certain free will does not exist. There’s really no solid evidence for it, and no credible scientific mechanic by which it could operate.

Quantum physics provides strong evidence that the future is not deterministic, though it can produce deterministic-like results in larger systems.

Also, specifically addressing your spoiler,

You react to choices the specific way you do because of experiences you’ve had previously.

Reverse time without changing anything, you’ll always make the same choices because you’re having the same thoughts each time every time, because you’ve been conditioned the way you are.

The universe doesn’t “know” where it’s going, but the plan is already in action. You can choose whatever you want to do, but if you were the same person in the same circumstance, you would and will always make the same decision.

Quantum mechanics are probabilistic, which serves as a good argument for the universe as a whole being probabilistic. The position of a single particle could change a great many things!

Religion warning:

I think free will exist but there is also a bigger plan. Like think of an open world video game, you can choose to do some things which will affect some other things but there are some parts fixed/determined to happen

Free will is way too vague of a concept, that it’s probably not worth pursuing the answer.

Hard determinist here. It doesn’t make the future predictable by me, but I don’t see how randomness could really occur. And then likewise there’s no such thing as free will.

Here is a good lecture from Robert Sapolsky on Human behavioral biology that will replace your question with more questions:
https://www.youtube.com/watch?v=NNnIGh9g6fA

Functionality, nondeterministic. But oddly even if the universe was deterministic, that doesn’t mean it’s computable, so even if you knew every single state of every single atom and everything was deterministic, you still couldn’t make accurate predictions

This is a weird application of the Halting Problem

Suppose that the universe is absolutely deterministic, and we have an omniscient machine that can 100% accurately predict the future because of this

Now, imagine we have another much much simpler machine that just inverts whatever input it has; when given input A, it outputs B. This can be a single if statement or even a simple electronic NOT gate, but the functionality of this machine is completely known

Now, connect the determining machine to the inverting machine, and ask the omniscient machine “what will the inverter machine output?”

Although the universe is deterministic and the machine is omniscient, it’s impossible to accurately predict the future without being wrong.

If the determiner says “A”, then the inverter says “B”, and if the determiner says “B”, then the inverter says “A”

Even though the inverter machine is highly simple in construction and it’s functionality is completely known, it’s still enough to make accurate predictions in a deterministic universe impossible, even for an omniscient machine, since simply making a prediction changes the outcome

The only way for the omniscient machine to be accurate is if it doesn’t at all interact with the universe that it’s predicting, at which case it ceases to be useful

So nothing within the universe can 100% accurately predict the future, regardless if it’s deterministic or not

Determinism seems far more likely. We just want to think we’re special. But if we have free will, why? What gave us that ability and assuming it is our brains then what is the cutoff? Do all animals have free will? What about plants? Bacteria?

Indeterministic + free-will doesn’t exist and can’t exist. You literally end in impossible contradictions if you entail its existence in a consistent universe (as in, one where everything that exists is subjected to the same natural laws).

As a side note for OP, Hisenberg has proven there’s no such thing as “knowing the initial condition”.