QM and Determinism: Can We Predict the Future?

[.Scott]

Even in time reversed interpretations, outcomes of individual observations are statistical. So I don't see that there is ANY strong argument for absolute determinism. It is merely a possibility in some interpretations.

That QM only provides statistical results does not indicate either determinism or non-determinism. If we knew the state of the entire universe in one cross section of time, QM, as we know it, limits what might come next - and in time reversal, what may have come just before.

But the conservation of information is much more interesting. If the changing of states is not exclusively dependent on the initial state and on the passage of time, then what else is it dependent on and how does that "what else" work in time reversal. In this case, breaking determinism appears to break the notion of time itself. If there is another parameter, beyond time, that determines how "now" turns into "next", then that other parameter would be another time-like dimension and our common perception of time as one-dimensional is at odds with physics.

 

[DrChinese]

1. That QM only provides statistical results does not indicate either determinism or non-determinism.

2. ...and our common perception of time as one-dimensional...

1. Statistical results is certainly an indication of in-determinism and is certainly NOT an indication of determinism. You would certainly expect a statistical distribution of results from a truly random set of processes.

It is a proof of neither. It is possible to have a sequence of results that appears random but is not. But you wouldn't specifically expect that.

2. One-directional might be a better description, as one dimensional allows time reversal.

 

[.Scott]

One-directional might be a better description, as one dimensional allows time reversal.

The directionality of time, that we see the past as inherently different than the future, is another topic.

My attack is against anything "inherently random" in how the universe changes states as time passes. If there is such a phenomena, you could describe it as in-determinism, but you would be more consistent with science in describing the apparent randomness as the result of another time-like parameter. After all, calling it "inherently random" means that you have decided not to address it any further as an concern of science. Whereas calling it a function of an independent time parameter (a second dimension of time) allows it to be treated more broadly.

 

[bhobba]

My attack is against anything "inherently random" in how the universe changes states as time passes.

Its a meaningless issue.

There is no way to tell the difference between something that is genuinely random and something that simply looks random.

That's why we have interpretations of that are inherently random, some that are deterministic, and even some like many worlds that are a bit unclear with a number of sometimes very long threads on this forum discussing it.

After all, calling it "inherently random" means that you have decided not to address it any further as an concern of science.

Any scientist knows that any assumption is up for grabs as science progresses. In fact this the hallmark of science.

Whereas calling it a function of an independent time parameter (a second dimension of time) allows it to be treated more broadly.

Exactly how such a strange idea has anything to do with the issue has me beat.

Thanks
Bill

 

[Johan0001]

If the QM notion of "conservation of information" is accepted, then there is certainly a very tight tie between one moment and the next.

This seems logical to me. However how does one quantify Information WRT Quantum mechanics?
Is it perhaps related to entropy?
If information is continuously conserved at least we have a history of some sorts.

If a change from one state to the next is not determined by the previous history of states , then QM cannot be complete , just an approximation.
Not chaos like a pebble in the stream as mentioned above , but a more accurate version, given a good statistical approximation.
But still just an approximation.

 

[vanhees71]

I still think that your statement "all physics is causal" is misleading, on multiple accounts. I think you would better say something like "initial value problem with the evolution equation in quantum theory has unique solution".

But that's causality expressed in a mathematically concise way! The evolution equation for the probability amplitudes, and thus the observable probabilities, tells you uniquely the state, given the initial state (provided you have complete knowledge of the Hamiltonian of the system).

It's still not a deterministic theory, because the exact knowledge of the states implies only the knowledge of probabilities for the outcome of measurements of observables for which the state is not a ray in the eigenspace of the corresponding self-adjoint operator. So not all observables are determined although the state is completely known.

Thus I stay with the definition given by Schwinger: Quantum theory is causal but indeterministic.

 

[DrChinese]

If a change from one state to the next is not determined by the previous history of states , then QM cannot be complete , just an approximation.
Not chaos like a pebble in the stream as mentioned above , but a more accurate version, given a good statistical approximation.
But still just an approximation.

Whether or not QM is complete is dependent on interpretation and definition. Is there a "more complete" version out there?

 

[Jano L.]

But that's causality expressed in a mathematically concise way! The evolution equation for the probability amplitudes, and thus the observable probabilities, tells you uniquely the state, given the initial state (provided you have complete knowledge of the Hamiltonian of the system).

Then your notion of causality is just that - property of the evolution equation. Quantum theory has more parts than that - in some events like measurement the equation is not applicable and the new ket vector has to be chosen based on the results of measurement, which as you say, cannot be found from the evolution equation.

So not all observables are determined although the state is completely known.

The state is known only before the measurement occurs. After the measurement of the atom position, the state vector has to be changed manually into new value which can be only found experimentally, or one can consider all possible results and pass on to probabilistic description of the new ket vector. Either way the new ket is not uniquely determined by the initial conditions and the evolution equation.

 

[Johan0001]

Whether or not QM is complete is dependent on interpretation and definition. Is there a "more complete" version out there?

I doubt it , and many years of advancement has taken place in QM , but I suspect we are far from ideal.
It took 200 years before a revised theory replaced classical mechanics.
Thanks for your input guys.