In which way does quantum mechanics disprove determinism?

  • I've heard this pop up in a discussion with my physicist/engineer roommates, but didn't care to ask at the time. Now I'm mighty curious about it. Wikipedia doesn't really seem to say much on this issue.

    From what I understand about the Uncertainty Principle, it says that there are certain properties of electrons and stuff that cannot be measured, and are therefore uncertain. Then Wikipedia (under indeterminism) states that Sir Arthur Eddington says that the Uncertainty Principle isn't really so because we can't measure these properties, but because turns out nature is indeterministic. At least that's what I took from those paragraphs. Even without my biased wording, it sounds more like an assertion than evidence.

    I've also read a few things about how other scientific conventions perceive the issue, like how a ball on the peak of a perfect mound might randomly roll down in any direction, and I'm still unconvinced. My belief of determinism is generally that if you knew every single variable that existed as a factor at the very beginning and birth of the universe, you could correctly determine all properties of any individual particle at any point in time.

    Could anyone provide some more background about this? Especially regarding quantum mechanics?

    You should look at a similar question I asked on the subject not too long ago. It may help clarify the confusion regarding fundamental nature of quantum physics in regards to the very idea itself being a positive claim as opposed to a "lack of knowledge" claim.

    Thanks for pointing me to your question. At first it wasn't evident, but reading these answers brought up that question for me.

    Although the uncertainty principle was originally proposed by Heisenberg as a limitation on measurement, it's now understood to be a limitation on what there is to be known about a physical system.

    I found the other day this video: This was a problem inside the scientific community, specially between Alberts Einstein and Niels Bohr, this is known as the Bohr–Einstein debates:

    Searle's Third Law: "Anything philosophers say about quantum mechanics is B.S. and quantum physicists aren't much better."

    Positing that quantum mechanics or 'uncertainty' by causal relationship, exercises any impact or interpretive value to any aspect of human experience, is the same as saying that the micro-organisms in the soil affect our ability to think. That is, that interchange and activity at the atomic and molecular level have no direct relationship when it comes to interpreting the nature of human experience. Any hypothesis which claims any connection is merely a case of 'reductionism' run amok. CMS

    There is interesting research that suggests changing the initial position of three interacting black holes by only a Planck length, can generate widely different outcomes Quantum mechanics suggests we can never measure to below that accuracy, so this points to limits on predicting the past, and to information possibly not being conserved.

  • I thought I would give a physicist's perspective here.

    There are two types of evolutions in quantum mechanics: unitary (or free) evolution and measurement. Free evolution is fully reversible and deterministic; a given operator takes a specific wave functions and maps it to a specific other wave function. The uncertainty comes from the non-unitary measurement evolution.

    Unfortunately, if you want to approach this problem from a realist point of view (how most people think of classical mechanics, etc) it becomes difficult to solve the measurement problem: i.e. what constitutes a measurement, where is the system and where is the measurement device? Isn't the measurement device + orginal system just a bigger system that should be undergoing unitary transformations? This question has puzzled many, with some notable scientists even linking measurement to the acts of conscious observers. But this is not a standard view.

    Most researchers on the foundations of quantum mechanics, however, usually side-step this question by taking the operationalist point of view. Tagline: "all we have is some procedures for setting up an experiment and the results of experiments". In this framework, you can derive Bell's theorem, which says that any phenomenon that is both deterministic and local must satisfy the Bell inequality. Quantum mechanics violates the Bell inequality (and there have been many experiments that mostly confirm this violation, there are some technical loopholes that need to be addressed in some of the experiments). This means that you must give up at least one: locality or determinism. Since without locality it becomes impossible to talk about causality, most people prefer not to give it up, and instead give up determinism.

    Thanks for this fantastic answer! I'm only unclear what you mean by the two evolutions in quantum mechanics; are you referring to branches of opinion or distinct sub-fields within the topic?

    Thanks, I meant evolution as in a transformation of state from time t to time t + 1.

    @ArtemKaznatcheev I don't see that locality is required for determinism. 'Action at a distance' makes perfect sense and is compatible with determinism, even if it seem incredible. So it isn't the violation of Bell's Inequality that makes systems non-deterministic, it is rather the statistical interpretation of the wave function presented originally by Born that is incompatible. A deterministic non-statistical interpretation has been presented by Bohm.

    That said, there are many problems with Bohm's approach to quantum physics (e.g. see Fine's excellent book, 'The Shaky Game'). So there is nothing wrong *in principle* with Bell and determinism, but there are many problems with the attempts so-far to create a deterministic theory (Einstein famously failed to do so).

    @adrianos I never said that locality is required for determinism. Read my second to last sentence; you have to give up either locality OR determinism. Most people prefer to give up determinism and keep locality. Bohm (who is linked in my answer as a realist) is a notable exception that preferred to give up locality in order to keep determinism. However, from my experience working in quantum computing, I do not feel that most practicing physicists share his views.

    Determinism works fine w/ a realist perspective if you consider that Many Worlds is strictly simpler than Collapse. EDIT: Not that you can determine/discriminate, from the starting point, whether you will end up in World1 or World2 because no matter which one your theory predicts, there will be a version of you in the other world thinking "Well, I guess that theory was wrong."

    It's a good answer. But calling some sect of people as non-notable, crack-pot etc., is too presumptuous and can be avoided. Since all the praxis of physics is based upon heuristic and empirical observations, the ontology is always missing. Since the knowledge gained out of epistemics, is subjective, we can never be sure to infer something objective from it. So non sense means that it's not in our mind, or brain to understand it. Before Galileo, sun in the middle was non-sense, and crack-potty attempt. @ArtemKaznatcheev

    So no science can formulate a consistent notion of reality, being axiomatic, always misses out on completeness. So there are many things yet to come, and we can't be so sure, to brand others easily. Thanks for your attempt, and good answer again, except that non-notable. Notable is again a kind of measurement, unless you make it, it wont appear, and there are still many non notable people, so it sounds demeaning intellect of many others, whose sweetness is getting wasted in desert wind, due to environmental circumstances.

    Would you mind clarifying by what you mean by "local" within the context of "any phenomena that is both deterministic and local".

    Also, would you mind elaborating on what you mean by "unitary" within the context of "The uncertainty comes from the non-unitary measurement evolution".

    Nice answer. For my two cents I would give up locality before determinism and feel there is no other way forward. For me QM is just further proof of the doctrine of the Upanishads, just as it was for Schrodinger and is for Mohrhof and others today. This keeps determinism but loses locality for the idea that space-time is not metaphysically real.

    Assuming "crack-potty" is a reference to the Free Will Theorem? I don't know what to make of it, and based on the source, I have to wonder if it's a "put on", more of an intellectual game than a proof. *(i.e. the idea that elementary particles have choice seems absurd, and possibly that's the point?)*

    I have revised the grammar in places. Excellent answer : +1.

    Non-local theories with retro-causality do not necessarily result in a paradox - one can imagine that they are "self-consistent" by the so-called _Novikov principle_ . The trick is whether or not any of the common non-local theories, e.g. Bohm, truly do end up being self-consistent and not contradictory (which will show up as the solution set of the equations being empty), and moreover, whether or not that even if there is consistency, the requirement may prune away so many solutions as to make a real difference in observable predictions.

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Content dated before 7/24/2021 11:53 AM