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.

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 an important question to ask is what “free will” actually is. I find people throw the term around without necessarily having a concrete definition for what they personally mean. When I use the term free will, I am saying that the the choices a sapient being makes would somehow be independent from all of the variables within the natural Universe. If it is dependent on natural variables (whether we know of them or not) this makes it deterministic, simply regular reactions to an unimaginably large domino effect.

The only hypothetical test I could conceive of would be if someone were able to rewind literally all variables of the Universe to a point in time just before decisions were made by another being, and doing this countless times and seeing if the outcome ever changes. I’d consider this to be entirely untestable, and as such I do not entertain the idea. For now I hold to what seems to be demonstrably true, which is that everything seems to operate and behave based on their properties, and react based on other variables which interact with them. With enough variables, we can make models to accurately predict the world around us, I do not expect our will to be any different.

Some entities are more deterministic than others. A rock is more deterministic than an animal and a human is less deterministic than an animal because its “causal inertia” is weaker: it can be influenced by more factors than the rock and is more unpredictable.

The question is underspecified. Why do you want to know if free will exists? What will you do differently if it does exist vs if it does not exist?

This is similar to questions like, “is water wet?” You can generate endless debate on the topic, but it’s all intellectual masturbation until you are genuinely looking for the answer to a specific question.

I’d say free will exists. Sure, you are shaped by your environment, your genetics and so on, but in the end you can still decide what you want to do. In theory I could simply quit my job tomorrow, wander off into the sunset and then drown in the next ocean. Or as someone brought up criminals, you could stab someone just trying to disprove the universe is being deterministic.

If you know every single atom in this moment and had unlimited computing power, you’d probably be fantastic at telling the weather. Or if you map every neuron in someone’s brain you might know what they are about to do next. But at this point you are just looking at the present data and can maybe calculate the next few seconds (but not even that is 100% sure, just a very good guess).

The question is how far forward would you be able to look just based on current and past data? A minute? A day? A month? At that point the whole thing breaks apart in my opinion. It’s like looking at the stock market where you have tons of past data and think you can predict the future simply based on that.

There’s so many complex sources of randomness, the most likely solution is that things are just that, random. And you can decide what you want to do with your own life, at least until you die (or don’t, who knows what the future brings). Honestly the whole question is dumb, there is no single being that knows everything, so it really doesn’t matter. In the grand scheme of things even humanity is just a tiny blip on the timeline and we’re with very high probability not unique. Just based on numbers there is a high chance other life forms have existed before us, might exist right now with us (somewhere else in the universe I mean, there’s also plenty on Earth) and will exist in the future.