Why is Randomness so Hard to Prove?

[Zygote]

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Quantum mechanics does not disprove determinism; it just suggests that completely accurate predictions of the future are currently beyond us.

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QM does NOT suggest that accurate predicitons are currently beyond us. QM says that the most htat can be known by anyone (whether it be a god, a superhuman or supermachine) is the wave function!

[Piers]

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[ QUOTE ]

Quantum mechanics does not disprove determinism; it just suggests that completely accurate predictions of the future are currently beyond us.

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QM does NOT suggest that accurate predicitons are currently beyond us. QM says that the most htat can be known by anyone (whether it be a god, a superhuman or supermachine) is the wave function!

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Quantum mechanics says that if you model a wave or particle using quantum mechanics then the most that can be know by anyone (whether it be a god, a superhuman or supermachine) is the wave function.

Also for the moment quantum mechanics appears the best model we have for such wave/partial dynamics.

It is important not to confuse model and reality. The choice to apply any model is always subjective.

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Quantum mechanics does not disprove determinism; it just suggests that completely accurate predictions of the future are currently beyond us.

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I agree that my language was slightly sloppy.

The original poster claimed that QM could be used to disprove determinism.

The point I was trying to make is that if QM is the best model we have, then the most our current use of QM could do is show that determining the future is currently beyond us.

I was buying in to his assumption that determinism does not exist within a QM model, but pointing out that a model cannot give results outside of itself.

Personally I think the whole QM thing feels like the projection of some structure onto a subspace. If we could step back we would be able to see a way of lifting everything to some super-space where all the QM paradoxes disappear. But that’s just me guessing in the dark.

[chezlaw]

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The original poster claimed that QM could be used to disprove determinism.


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QM is not inconsistent with determinism and could never be used to disprove determinism. To see why this is true, imagine a deterministic simulation of a QM universe

[unless you make non-determinism an assumption of QM but its not a neccesary assumption]

chez

[Piers]

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It just seems to me there are plenty of things without determined outcomes. Why do we need QM to disprove determinism?

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[ QUOTE ]
The original poster claimed that QM could be used to disprove determinism.


[/ QUOTE ]
QM is not inconsistent with determinism and could never be used to disprove determinism. To see why this is true, imagine a deterministic simulation of a QM universe
[unless you make non-determinism an assumption of QM but its not a neccesary assumption]
chez

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That’s fine. If QM is not inconsistent with determinism, I do not need to do anything to show that QM does not disprove determinism, which is all I was trying to do.

I was instead making the point that the details of a particular model of some facet of the universe that is currently in vogue cannot be used to disprove determinism; which seems to achieve the much the same result.

[chezlaw]

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It just seems to me there are plenty of things without determined outcomes. Why do we need QM to disprove determinism?

[/ QUOTE ]

[ QUOTE ]
[ QUOTE ]
The original poster claimed that QM could be used to disprove determinism.


[/ QUOTE ]
QM is not inconsistent with determinism and could never be used to disprove determinism. To see why this is true, imagine a deterministic simulation of a QM universe
[unless you make non-determinism an assumption of QM but its not a neccesary assumption]
chez

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That’s fine. If QM is not inconsistent with determinism, I do not need to do anything to show that QM does not disprove determinism, which is all I was trying to do.

I was instead making the point that the details of a particular model of some facet of the universe that is currently in vogue cannot be used to disprove determinism; which seems to achieve the much the same result.

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Yeah but you'll never convince the evidence junkies your way, they'll start wittering on about the probability that randomness exists [img]/images/graemlins/smile.gif[/img]

chez

[gumpzilla]

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QM is not inconsistent with determinism and could never be used to disprove determinism. To see why this is true, imagine a deterministic simulation of a QM universe

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How do you propose to recreate the predictions of quantum mechanics deterministically?

[chezlaw]

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[ QUOTE ]

QM is not inconsistent with determinism and could never be used to disprove determinism. To see why this is true, imagine a deterministic simulation of a QM universe

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How do you propose to recreate the predictions of quantum mechanics deterministically?

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All that's needed is to show that our universe could be running as a simulation on a deterministic computer. (I'm obviously not claiming that's what is going on)

Computationally QM is like late evaluation, you never calculate a value until its needed.

Consider the up/down spin of two entangled particles (pretty much the classic QM experiment). This is consistent with a computer simulation that doesn't calculate the up/down values until they are needed for something. When one of the particles is force by measurement to have an up/down value the 'program' pseduo-randomly allocates the values up/down to the particles. This happens at the speed of the computer which is many orders of magnitude greater than the max speed within the simulation.

That's a bit of a hurried explanation but ask more if its not clear (or shoot it down in flames)

chez

[gumpzilla]

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Consider the up/down spin of two entangled particles (pretty much the classic QM experiment). This is consistent with a computer simulation that doesn't calculate the up/down values until they are needed for something. When one of the particles is force by measurement to have an up/down value the 'program' pseduo-randomly allocates the values up/down to the particles. This happens at the speed of the computer which is many orders of magnitude greater than the max speed within the simulation.

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The pseudo-randomness is key here. It means that you've essentially put forth a hidden variable theory, since we can completely characterize the expected measurements of various quantities (since the pseudo-random generator is presumably deterministic.) This might be acceptable, but thanks to Bell's theorem it has consequences about what your theory needs to look like, and thus might run into problems with reality. For this, and some other reasons (the computer that's going to classically simulate our QM universe is going to be mind-bogglingly huge compared to our universe itself), I don't think that the prospect of QM all being a deterministic simulation (some kind of brain-in-vat exercise writ large) is terribly realistic. I guess that's not your point, but it does at least suggest that there is strong evidence for inherent randomness.

I haven't really read the rest of the thread, but I'll make a comment about randomness, one that I'd be surprised if it hasn't already been brought up. Even in the face of perfect determinism, there is such an incredible degree of complexity that there are many things that are going to be essentially random in the end because you just can't control all of the important parameters precisely enough. And in the end, that's what's important about randomness anyway.

[chezlaw]

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The pseudo-randomness is key here. It means that you've essentially put forth a hidden variable theory, since we can completely characterize the expected measurements of various quantities (since the pseudo-random generator is presumably deterministic.) This might be acceptable, but thanks to Bell's theorem it has consequences about what your theory needs to look like, and thus might run into problems with reality. For this, and some other reasons (the computer that's going to classically simulate our QM universe is going to be mind-bogglingly huge compared to our universe itself), I don't think that the prospect of QM all being a deterministic simulation (some kind of brain-in-vat exercise writ large) is terribly realistic. I guess that's not your point, but it does at least suggest that there is strong evidence for inherent randomness.

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I'm not exactly sure what 'hidden variable' means but assumed it meant that the information that will decise the up/down spin is 'hidden' within the particle (or at least in the locality of the particle). If so the simulation is not an example of hidden variableness.

It is consistent with Bells inequalities as I understand it. Bell' idea is to show that either QM is random or locality is violated. The simulation violates locality (in a way consistent with the results of relativity) and so isn't bothered by bells result.

As for whether its realistic or not, thats beside the point here. The simulation is enough to prove that QM is consistent with determinism. [I don't think simulation or brain in the vat is realstic either but that doesn't mean that the universe we observe isn't entirely natural but a bit wierder than we currently think]

[Edit; Although I talk like I'm certain that's just my style (or lack of it). I originally posed this idea as a question and to the limits of my understanding it seems right. If someone can explain why QM isn't equivalent to late evaluation then I'd be very interested because that's how I currently think of QM]

chez

[Trantor]

[ QUOTE ]
[ QUOTE ]
The original poster claimed that QM could be used to disprove determinism.


[/ QUOTE ]
QM is not inconsistent with determinism and could never be used to disprove determinism. To see why this is true, imagine a deterministic simulation of a QM universe

[unless you make non-determinism an assumption of QM but its not a neccesary assumption]

chez

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I think you've alluded to a computer simulation of the universe before and here you put it forward as a possible (ie in principle) approach to show the QM is not inconsistent with determinism. BUT, this assumes it is possible, in principle, to carry out such a computer simulation wheras QM says this is not possible (as QM is understood at present, ie no hidden variable theory)