What does it mean that I have free will? If we can define free will like this:
If in a deterministic universe, no observer B can 100% correctly predict the behavior of subject A, except when B is in the future of A, we can say that subject A has free will.
We can prove that free will does exist in a universe where light speed is not infinite, even when we don’t consider quantum randomness. Here is the proof:
In a deterministic universe, the information of an event A (or in other words the behavior of a subject A) can be completely known, only if its prior states (or its causes) are completely known.
In a universe where light speed is not infinite, all the causes of an event A, lies on or inside its past light cone. If you don’t know all the causes of the event A, there will always be some uncertainty about A.
Light cone of event A
According to this picture, we can see that only observer B3 is able to know all the prior states of event A, because B3 is in the future of A. It’s impossible for B1 and B2 to know, for example, event C which may affect event A. Because C is not inside or on their past light cone.
For example, when you are chatting with your friend, you will never be able to anticipate that there might be a gamma ray photon hit their brain neurons from the far side of you and unpredictably change their mind.
(Some people may argue that there’s no free will in the presence of an all-knowing God. But that’s another story.)
Why Free Will is NOT an illusion
(This post contains some thought about gACI)
What does it mean that I have free will? If we can define free will like this:
If in a deterministic universe, no observer B can 100% correctly predict the behavior of subject A, except when B is in the future of A, we can say that subject A has free will.
We can prove that free will does exist in a universe where light speed is not infinite, even when we don’t consider quantum randomness. Here is the proof:
In a deterministic universe, the information of an event A (or in other words the behavior of a subject A) can be completely known, only if its prior states (or its causes) are completely known.
In a universe where light speed is not infinite, all the causes of an event A, lies on or inside its past light cone. If you don’t know all the causes of the event A, there will always be some uncertainty about A.
According to this picture, we can see that only observer B3 is able to know all the prior states of event A, because B3 is in the future of A. It’s impossible for B1 and B2 to know, for example, event C which may affect event A. Because C is not inside or on their past light cone.
For example, when you are chatting with your friend, you will never be able to anticipate that there might be a gamma ray photon hit their brain neurons from the far side of you and unpredictably change their mind.
(Some people may argue that there’s no free will in the presence of an all-knowing God. But that’s another story.)