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It might seem logical to presume that the exact state of the world around us could have been predicted given a big enough computer to analyse all the particle's interactions and what not. Determinism seems to be logical.

Then comes quantum computing. Since a collection of entangled qubits are only coherent when isolated from their environment, is this new information being fed into our known universe system? Whats going on here? Since you could hypothetically have hardware that starts manipulating particles as a result of these isolated quantum wave collapses, does this put the nail in the coffin of the deterministic universe?

Or are we just awaiting a mechanism by which these wave function's chose the value to collapse to (quantum foam geometry or something)? As far as I understand we don't yet know how the wave function choses its collapsed spin state except that statistically it follows a predictable probability spread.

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  • $\begingroup$ There are too many questions here. $\endgroup$
    – DanielSank
    Commented Jun 10, 2014 at 14:46
  • $\begingroup$ Sorry, the main question is "is quantum computing compatible with determinism (interaction of particles and/or their corresponding fields)". Since quantum computing is by definition isolated from their environment how can it be consistent with the pool table analogies of determinism? @DanielSank $\endgroup$
    – Mike S
    Commented Jun 10, 2014 at 23:12
  • $\begingroup$ You should edit your question instead of putting the clarification in a comment. I think people are ignoring this question because it's all over the place. $\endgroup$
    – DanielSank
    Commented Jun 10, 2014 at 23:52

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Quantum mechanics does not contradict determinism. The relevant equation of motion is something like the Heisenberg equation of motion which predicts how observables change over time. Those observables are Hermitian operators not single numbers. They represent a larger structure than the universe we see around us, which under some circumstances can be approximated by a set of approximately non-interacting parallel universes:

http://arxiv.org/abs/quant-ph/0104033.

Collapse does not happen. All that happens is that when information about the outcome of a measurement spreads it is no longer possible for versions of the same system that produced different outcomes to interfere:

http://arxiv.org/abs/0903.5082.

You can't predict what the outcome of the experiment will be because there is no single fact of the matter about what outcome you will see. Rather there will be different non-interacting versions of you for each outcome.

The probabilities in quantum mechanics have nothing to do with a lack of determinism. They are a result of applying decision theory to quantum mechanics:

http://arxiv.org/abs/quant-ph/9906015

http://arxiv.org/abs/0906.2718.

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  • $\begingroup$ Hmm so your answer posits the multi-verse 'solution' for quantum mechanics. It seems to just fling the solution to a space where by feature of its externality to our universe can never be tested. In Roger Penrose's version of cosmology (which I believe throws out the multi-verse idea) is quantum mechanics still deterministic? $\endgroup$
    – Mike S
    Commented Jun 11, 2014 at 7:08
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    $\begingroup$ Two things. (1) The MWI is experimentally testable. It provides precise predictions for what probabilities we should expect to see in experiments. If those predictions are wrong so is the theory. If we're going to discount the existence of anything we can't detect directly, then the core of the sun and dinosaurs must be discounted since nobody has seen either of them. (2) If Penrose provides an equation of motion for his theory, including equations of motion for the collapse, it may be testable, otherwise it is not. $\endgroup$
    – alanf
    Commented Jun 11, 2014 at 8:49
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    $\begingroup$ Saying that the MWI is testable because it makes predictions totally misses the point. The claim that the MWI is better than other quantum interpretations requires some set of predictions that differ from those made by other quantum interpretations. And while I am not an expert in the foundations of QM, last I heard there are no such testable predictions. $\endgroup$
    – dmckee --- ex-moderator kitten
    Commented Aug 29, 2015 at 18:52
  • $\begingroup$ @dmckee There are three types of interpretations. (1) Claims that the equations of motion given by quantum mechanics are universally true, which gives the MWI. (2) Claims of some specific departure from those equations, such as the GRW theory. (3) Vague assertions about those equations being wrong in some unspecified way, e.g. - the Copenhagen and statistical interpretations. (3) is difficult to test because it is vague, and ought to be rejected for that reason alone. Some tests have been proposed, see chapter 4 of "Quantum Concepts in Space and Time" ed. Penrose and Isham. $\endgroup$
    – alanf
    Commented Aug 30, 2015 at 19:59

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