# Quantum indeterminacy

#### Magical Realist

Valued Senior Member
What is the basis for quantum indeterminacy and does it refute the claims of causal determinism?

Causal determinism: "Causal determinism is, roughly speaking, the idea that every event is necessitated by antecedent events and conditions together with the laws of nature."-- https://plato.stanford.edu/entries/determinism-causal/

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One of the main differences between classical mechanics and quantum mechanics is the fact that QM is probabilistic in nature. You cannot say with certainty where a particle will end up. You can only assign a probability. You also cannot say what path it took.
If a particle decays there may be more than one way it does that.
There are a few features of QT that are not deterministic.
Heisenberg developed a principal on the uncertainty of "knowing" but that would be better coming from one of the other guys I think.

There are two properties of "causal determinism" - the first, that Pinball1970 has mentioned, is the deterministic property, and, no, QM is not generally considered deterministic in the usual sense. At best it could be described as probabilistic determinism. So where determinism means that if you have input A then this always leads to output B, in QM we might be able to state that if we have input A then this always leads to the probability-function B... but you may end up with any of the possible outcomes within that probability function (the likelihood of each being described by the function). If this was due to "hidden variables", for example, then determinism may still exist just hidden to the extent that the outcome appears indeterministic.
Of course, there are some interpretations that would have the entire universe as a single wave-function and thus deterministic as a result.

The second property is causal - and specifically the antecedent cause - i.e. cause and then effect. I think the answer to whether QM defies this part is that there is no definitive answer, although the general consensus would seem to be that it does not defy causation (cause preceding effect). There may be some studies that suggest it does, some that suggest not, and interpretation is key. Does the cause/effect need to convey information from cause to effect, for example, and if so, does QM allow effect to precede cause - or indeed any transference of info FTL? And what of uncaused events?

I'll try and dig into this latter if I get time, and see if I can come up with any studies / reports etc one way or the other. It's piqued my curiosity.

There are two properties of "causal determinism" - the first, that Pinball1970 has mentioned, is the deterministic property, and, no, QM is not generally considered deterministic in the usual sense. At best it could be described as probabilistic determinism. So where determinism means that if you have input A then this always leads to output B, in QM we might be able to state that if we have input A then this always leads to the probability-function B... but you may end up with any of the possible outcomes within that probability function (the likelihood of each being described by the function). If this was due to "hidden variables", for example, then determinism may still exist just hidden to the extent that the outcome appears indeterministic.
Of course, there are some interpretations that would have the entire universe as a single wave-function and thus deterministic as a result.

The second property is causal - and specifically the antecedent cause - i.e. cause and then effect. I think the answer to whether QM defies this part is that there is no definitive answer, although the general consensus would seem to be that it does not defy causation (cause preceding effect). There may be some studies that suggest it does, some that suggest not, and interpretation is key. Does the cause/effect need to convey information from cause to effect, for example, and if so, does QM allow effect to precede cause - or indeed any transference of info FTL? And what of uncaused events?

I'll try and dig into this latter if I get time, and see if I can come up with any studies / reports etc one way or the other. It's piqued my curiosity.
Yes, I can't see how QM can be argued to defy causality. But it does seem to defeat strict determinism, at least at the atomic level. In practice, almost all phenomena we are concerned with are determined by the behaviour of large enough ensembles of matter or radiation that this lack of determinism in principle can be ignored.

I came across this short article on quantum indeterminacy which argues that it is a real indeterminate property of reality and not just due to our not knowing. That causal determinism is really refuted by it. Being but a lowly layman in this area, I submit it for review by the other more educated posters here.

https://hilo.hawaii.edu/~ronald/310/Quanta.htm

"It is important that we understand what modern physicists say about quantum indeterminacy. It is a very unintuitive notion, and I sympathize completely with people who distrust it. My own reaction to it was this: "This can't be right. They must be confusing not knowing the event's cause with the event not having a cause."

If physicists were confused about this, then we wouldn't need to take them seriously. But they are not confused about this. They know the distinction, and they continue to believe in quantum indeterminacy (QI)."

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I came across this short article on quantum indeterminacy which argues that it is a real indeterminate property of reality and not just due to our not knowing. That causal determinism is really refuted by it. Being but a lowly layman in this area, I submit it for review by the other more educated posters here.

https://hilo.hawaii.edu/~ronald/310/Quanta.htm

"It is important that we understand what modern physicists say about quantum indeterminacy. It is a very unintuitive notion, and I sympathize completely with people who distrust it. My own reaction to it was this: "This can't be right. They must be confusing not knowing the event's cause with the event not having a cause."

If physicists were confused about this, then we wouldn't need to take them seriously. But they are not confused about this. They know the distinction, and they continue to believe in quantum indeterminacy (QI)."
Yes this is standard. Indeterminacy is intrinsic. It has nothing to do with our limited powers of knowledge as observers. It is a consequence of the Fourier transform relationship between some pairs of properties, i.e. a consequence of the wavelike nature of QM entities.