B Does the Schrödinger Equation Imply a Deterministic Universe?

[Physics Slayer]

TL;DR Summary

Does quantum mechanics imply a deterministic or non deterministic model of the universe?

The entire universe has a single very complicated wave function $\psi$, and if we plug this into the schrödinger equation will that mean we live in a deterministic universe? (whatever happens and will happen was already predetermined at the time of the big bang. the initial conditions of the universe, i.e. $\psi(t=0)$ was set at this time)As the schrödinger equation will tell us how the wave function will evolve, will that mean that a theoretical creature like Laplace's demon could see the future and the past?

I have heard people before Quantum Mechanics believed that everything was deterministic and that we have no free will, if we knew the forces acting on every particle we could theoretically construct the the future and peer into the past, but once we got to know about the fundamentally random collapse of the wave function, this model of a deterministic universe could not hold anymore?

I am not sure if I am allowed to ask about free will(on a science forum, it's more philosophy?).

 

[DrChinese]

Summary:: 1. Does quantum mechanics imply a deterministic or non deterministic model of the universe?

2. The entire universe has a single very complicated wave function $\psi$, and if we plug this into the Schrödinger equation will that mean we live in a deterministic universe? (whatever happens and will happen was already predetermined at the time of the big bang. the initial conditions of the universe, i.e. $\psi(t=0)$ was set at this time)As the schrödinger equation will tell us how the wave function will evolve, will that mean that a theoretical creature like Laplace's demon could see the future and the past?

I have heard people before Quantum Mechanics believed that everything was deterministic and that we have no free will, if we knew the forces acting on every particle we could theoretically construct the the future and peer into the past, but once we got to know about the fundamentally random collapse of the wave function, this model of a deterministic universe could not hold anymore?

3. I am not sure if I am allowed to ask about free will(on a science forum, it's more philosophy?).

Some big questions in here! And each is good for many a debate.

1. Generally speaking, what we know about QM implies a non-deterministic universe. There are interpretations of QM in which determinism is maintained (Bohmian Mechanics being the best known of those). I would recommend checking out the Quantum Interpretations and Foundations subforum to learn more. That is the proper spot to discuss those.

https://www.physicsforums.com/forums/quantum-interpretations-and-foundations.292/2. Although the Schrödinger itself is deterministic, it cannot be used to predict the outcome of any specific experiment when the probability is not certain (0 or 1). In those cases, experiments show that outcomes are random as best as anyone can tell. There does not appear to be any information available to us to predict outcomes, and theory offers us no particular hope that such information might be discovered in the future. (Of course, anything is possible.)

Don't forget that we have the Heisenberg Uncertainty Principle as well. That limits knowledge about non-commuting properties of quantum systems.3. Keep the discussion about free will in the Interpretations subforum alongside discussions that relate to the science, and you should be fine.

 

[PeterDonis]

Summary:: Does quantum mechanics imply a deterministic or non deterministic model of the universe?

It depends on which interpretation of QM you adopt; some (such as the MWI or the Bohmian interpretation) are deterministic, while others (collapse interpretations) are not.

As @DrChinese has already mentioned, discussions of QM interpretations belong in the interpretations subforum, not here.

As far as practical applications of QM go, they have to treat things as non-deterministic since we can't use QM to predict exact experimental results in general.

I am not sure if I am allowed to ask about free will(on a science forum, it's more philosophy?).

Free will discussions in general are philosophy and are off topic in the science forums here. (You might be able to discuss it in General Discussion.)

Free will discussions in the context of specific papers on QM interpretations that take some definition of "free will" and apply it to some QM interpretation are permissible in the interpretations subforum, although they still get moderated carefully.

 

[mattt]

I have heard people before Quantum Mechanics believed that everything was deterministic and that we have no free will...

We don't have "free will" (as normally understood by people) either in a stochastic universe...

 

[PeterDonis]

We don't have "free will" (as normally understood by people) either in a stochastic universe...

As has already been pointed out in response to the OP, discussions of free will are in general off topic in the PF science forums. That includes this thread.