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Space time has existed from the beginning of the universe and until its end and humans exist on 3D plane. Due to its limitations, it is only able to experience one period of spacetime, like being inable to travel backward or forward in time.

Although the passage of time for said organism may indicate that "future" hasnt happened and actions can change the future. However, an hypothesis that humans is merely experiencing the spacetime from its birth, from its inabllity to comprehend the whole length of spacetime from its birth to death?

like being viewed from an 4D organism that is able to experience different period of spacetime, it will be able see an organism from its birth to death, sounds like determinism?

tldr: spacetime has existed throughout the beginning and end of universe and are humans merely experiencing spacetime without free will?

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The question of whether we exercise free will or behave simply as machines is not one that can yet be decided by physics- we do not understand sufficiently well the nature and cause of consciousness.

If all matter behaves in accordance with deterministic physical laws then we do not have free will- only the illusion of it, since our brains will respond to any given set of inputs and circumstances in a deterministic way.

In order for free will to exist, it is necessary that consciousness can operate with a degree of independence from deterministic physical laws, and, importantly, cause physical changes, since we display the results of the exercise of our will by movements, speech etc, which are physical phenomena.

The question of whether future time already exists as part of an eternal block of spacetime, or whether, say, only the present moment exists, is another that cannot yet be settled by physics. It is possible to find every sort of opinion on the matter by physicists and philosophers alike- try searching 'the philosophy of time' on the internet.

The idea of future time already existing is taken a step further by some people who believe that all future events exist in spacetime- and that we have just yet to encounter or experience them. That view, at least, does not seem compatible with physics- quantum effects, as far as we know, are inherently probabilistic, so the future course of events cannot be predetermined but will unfold according to the results of inherently probabilistic outcomes occurring moment by moment.

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  • $\begingroup$ I do agree with your second paragraph. But there are many philosophers who disagree with that. Ancient Stoics were the first to argue that determinism and free will are compatible. And even today there are philosophers who argue that they are compatible. $\endgroup$ Sep 21 at 7:15
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    $\begingroup$ Indeed. At the risk of being patronising towards them, that is because they are not physicists but philosophers. $\endgroup$ Sep 21 at 8:32
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Space time has existed from the beginning of the universe and until its end

Spacetime does not live in a time dimension - instead, all time lines are included in spacetime. So it always "exists", beyond any "from-to" interval. In fact we need spacetime to define such an interval. As for the universe, being all what happens in space (and time, inevitably), it is also not exterior to spacetime.

humans exist on 3D plane

Each human exists on a timelike curve linking birth and death events. Each event in that curve is a 4D point.

like being viewed from an 4D organism that is able to experience different period of spacetime, it will be able see an organism from its birth to death, sounds like determinism?

As stated above, humans are represented as 4D curves. In physics there is no way to define an external point of view allowing to observe them "from above", so to say. Spacetime as such is a tool used for defining the relationships between all physically meaningful points of view, but it does not provide in itself some "higher" point of view (at least not as a well-defined physical construct - I am not talking about the intuitive picture people could have of an all-encompassing " block universe" here).

So, there is no organism that physics could model that would be able to encompass in its view the whole existence of an human.

tldr: spacetime has existed throughout the beginning and end of universe and are humans merely experiencing spacetime without free will?

Free will would geometrically translate as: a 4D timelike curve (associated to a specific human experience) that is not "set in stone" (free will making the curve itself "free" in some sense, with presumably only the birth event ensured to be a specific one).

Now as we just saw there is no way to determine if a 4D curve is "set in stone" or not. There is just no such encompassing point of view.

And so, physics simply does not provide the conceptual framework to answer this question, and in fact not even to ask it.

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Consider an electron in superposition. Will the electron collapse? will depend on if it will be measured. So until it's measured, there is no meaning in talking about its position. That means that future of an electron is not deterministic. And if the future is non deterministic, that would mean that there will more than one possibility. And hence there can be more than one version of future. If the 4D organism sees a 3D organism, it would see its birth to death (instantaneously) in more than one reality and that is not determinism.

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