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I think it is pretty clear what is meant with local variables. In the case of polarised photons the question would be: is there some physical attribute of the photon that determines for a certain angle of the measuring device what polarisation will be measured? It means that when a polarised photon pair is created, both photons already have this attribute. Bell's theorem proves that if this were the case, we cannot get the predictions that QM makes. In experiments where this can be tested it turns out that QM's predictions are correct. So it proves that in these situations there are no local variables that determine exactly what the measurement will be. Of course that does not mean there is no determination at all. E.g. when both measurement devices are oriented exactly the same, I can predict for 100% sure that if I detect a photon on one side, I will also detect the photon at the other side. But on average, for random angles, QM's predictions differ from any possible theory that assumes that the measurement depends on any attribute the photons already have before measurement. This is even a finer example. Another source: MinutePhysics

Bell's theorem proves that not any possible theory that contains local variables can reproduce the predictions of QM. If you think it doesn't, then show us the error in Bell's theorem. You really should read the article Mordred linked to, I had a small glance at it. Here is its central statement: No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics. Follow his argumentation, and tell us where the author makes an error.

Until you prove that Bell's inequality is wrong, your words are empty. Go ahead, and get your Nobel-price. Really, the inequality is not difficult to understand, so it must not be too difficult to disprove it, and show why thousands of physicists are deluded. You argue from ill faith.

You are incredible. You show that you still do not understand Bell's theorem. Maybe I was a little ambivalent when I wrote ' Local variable theories comply to Bell's inequalities' here. So I'll try once again: Any possible theory (even a theory we haven't thought up yet) that contains local variables per definition obeys Bell's inequalities. The predictions of QM do not obey Bell's inequalities. The predictions of QM turn out to be correct in Bell test experiments. Conclusion: It is impossible that there are local variables in Bell like situations. Corrolarium: if it is impossible that there are local variables, then it is also impossible that there are hidden local variables. The interesting thing is that number 1. is the easiest to understand, if you put some concentration in it. You do not need any knowledge about mechanics, quantum or not, to understand it. Just google. Mordred's 'Chapter 4' surely explains it all, but it is not aimed at lay persons, as you obviously are one. After you understood point 1 you must believe the points 2 and 3. Of course, if you are really at it, you could learn QM, and then understand that 2 is correct too. Then you only have to believe number 3, but I am pretty sure after understanding number 2 you do not really doubt that the experiments done show exactly what they did: confirm QM, and therefore rule out the possibility of local variables. But if you do not even try to understand number 1, I can only say that your standpoint is done from ill faith. So your task, if you want to stick to your view point, is to refute number 1. If you can't, you must logically accept that it is proven that there are no local hidden variables. Any belief or opinion of yours is empty if you do not take the bull at the horns. Of course there is! We can measure when a photon arrives at a detector, we can measure the projection of its polarisation, but what we cannot do is measure its polarisation as it really was before measuring: simply because there is no local reality behind the scenes. Again, you do not understand QM enough, otherwise you would not say this. Again, only ill faith can explain you saying such things again and again. Again, a hidden variable theory might be possible: it is not ruled out by Bell's theorem. But local hidden variables logically cannot reproduce the empirically proven correct results of QM. I can only say: groundless metaphysical considerations, free flowing from any physics.

Blueyedlion, I suggest your read this small Wikipedia article on soundness. This should help you to understand what logic is, and how logical arguments (in the logic sense of the word!) differ from true statements. Oh, and, validity adds some more simple examples.

So, Itoero, when Mordred is correct: then you are just citing papers without understanding them. No hidden variables.

Randolpin, I would suggest that you start reading here. This was a topic in this forum already. But of course, if you have other insights or questions, feel free, but I for myself do not want to repeat the whole discussion.

Yes. Because the predictions of QM turn out to be correct. Must I spell it out for you? 1. Local variable theories comply to Bell's inequalities 2. The predictions of QM do not comply to Bell's inequalities. 3. The predictions of QM turn out to be correct in Bell test experiments. Conclusion: There are no local variables in Bell like situations. Corrolarium: if there are no local variables, then there are neither hidden local variables. On quantum level there is a tiny bit of 'disorder'. No idea why you think that. As you obviously do not understand the Bell theorem and its consequences, you say things that are far over your head. Let me know if it is interesting. Seems above my head. But at least I have the strong impression that has not much to do with local hidden variables.

Bell's theorem shows that no local hidden variable theory can reproduce the predictions of QM. If you leave out the word 'local', then the discussion is open. But I really doubt that we can look behind the scenes of what we observe. There are no observations we can do below the level of quantum events: we measure photons, or electrons arriving at screens or in counters. Do you suggest that there is some mechanism in photons and electrons?

No, because we have empirical proof that local hidden variable theories impossibly can reproduce the predictions of QM. You simply do not understand Bell's inequalities and the fact that QM violates them.

Yes. No.

It is mathematically proven that the predictions of QM are inconsistent with theories with local variables. It is empirically proven that QM's predictions are correct. You behave like a creationist who cannot accept scientifically proven facts. So you did not learn anything. Your opinion is against established science.

Of course. But you have no argument anymore that for typical QM processes every event is locally caused. If you still think so, you are denying established, empirically proven science. Repeating the arguments you already have given will not help.

Well, what do you think of the reactions in that thread? No physicist supported your view, I think on good grounds. Do you still hold to the view that the world is determined, with local causes?

This is misuse of the word 'logic'. Logic has nothing to with how people experience the world. It is about how truth of propositions are related. One can study this independent of what proposition you think are really true. 1. If the world is a disc, one cannot travel around the world. 2. The world is a disc. Conclusion: One cannot travel around the world. This is a logical valid reference. Only proposition 2 happens to be wrong. But the argument is correct.

But there is empirical proof! Why do you repeat this over and over again? QM's predictions violate the Bell inequalities. QM's predictions turn out to be correct. Bell's theorem says that no theory based on local (hidden) variables can reproduce QM's predictions. So it is proven there are no local hidden variables. You behave as a trisector who does not understand the difference between 'nobody has found a method to trisect an angle' and 'there is mathematical proof that trisection of an angel is impossible'. Your argument 'absence of evidence is not evidence for absence' is not valid: there is evidence for absence! Again: repeating the same argument over and over again does not make it more true. According to QM there is enough order to explain the order of the universe. The 'uncaused' events average out to a for nearly all practical, daily purposes determined universe. Why do you think did it took so long in our history of science that this statistical behaviour of matter was discovered? Because we do not notice it in our daily life

You can think that, but no such influences are found. So at this moment you only express a belief, not grounded in any science. Eh, yes? And what? Just translate correctly 'characteristic time' with 'half life', and it really is mainstream science. Note the use of the word 'spontaneously', which in this context means, 'having no cause'. Same as above: there is no empirical proof of such a cause, or causes. There are only strong arguments for the opposite. Do not forget: QT works. And really, as Strange already noticed: you think there must be causes, because you believe determinism must be true (begging the question). But until now you have not given any convincing argument, except misinterpretations of Bell-like experiments. Pure formally, you might be right. But it is a mathematical fact that that QM violates Bell's inequality. And all empirical experiments point to the fact that QM's predictions are correct. Of course you have heard about the 'loopholes'. But they are closed more and more. See e.g. here. In the light of the empirical evidence, you are inconsistent here. Or you believe that QM is wrong. Given above. This is vague as vague can be. Unless you come with a mathematical description, that can be tested empirically, you have nothing more than your belief that determinism must be true.

Of course, that is possible. But I would say that non-locality is just as 'spooky' as uncaused events. No, no, that does not work. If decaying particles were just 'leaking energy' continuously, all decays of a certain kind (e.g. muons) would take just as long. We would not have a halflife, but an exact lifetime, the same for all muons. But we know that is not the case. But of course a decaying muon is not an example of non-locality. You made this error already our discussion in the philosophy section. QM events are caused, but not exactly. A bit of indeterminism does not drop all relations with properties of the environment, it does so only a tiny bit. Why do you think it is difficult to realise Bell experiments? You do not seem to understand the character of Bell's theorem. In Bell-like experiments, it is not so that we cannot measure precise enough. Bell's theorem states that no local variable theory can reproduce the predictions of QM. So what we must do is setup situations in which QM predicts something that does not fit Bell's inequality. These experiments have been done, and QM's predictions are right. That proves that local variables (hidden or not) do not play a role. I am wondering what exactly your viewpoint is: is causality in your view 'saved' by non-local causes, or by hidden local variables? You use both in your arguments.

OK. And? Sources?

I think that you forget people can do something, without explicitly knowing what, or how they are doing it. This is obviously true for speech (children can speak without knowing grammar explicitly, same for people who never were at school). So you do not necessary need formal logic to make valid arguments. Also, you should distinguish between the chronological order of discovery and, well, logical dependency: one can do logic without doing math, but doing math without logical argumentation is of course impossible. Same for physics and math. Edit: see that Ophiolite made a similar point already.

Randolpin, you have a strange idea about what logic is. Logic tells us e.g. what valid arguments are, when propositions are contradicting each other, etc. What logic definitely isn't is a source of truth about empirical reality. The example you gave here are definitely not examples of logic. Logic tells us e.g. when you know on other grounds some true propositions, what follows from these. So except tautologies (A is the case or A is not the case) which are always true, logic produces no truths on its own. But it tells us how the truth of propositions depends on the truth of others. So it is an absolutely necessary tool in science, and even more in mathematics.

I am a bit in a dangerous area here, because I am not a physicist. But I think the established interpretation is this: particles are correlated with all particles in their light cones, or better all particles they ever interacted with. But if a particle is entangled with trillions of other particles, there is no way that you can see this. But please, raise your question in the QT forum, where more professional physicists are around. That's a hard one. But you can say this of any experiment. I can only say that Bell's theorem is generally accepted, and given that the predictions of QM in EPR-like experiments turn out to be correct, there cannot be local causes. If you doubt this fact, please also open a thread in the QT forum. Late Night edit: Maybe you can chime in here?

It is not illogical. The only thing is that if you try to picture what happens with objects and movements as you know them from daily life, you fail. It is not logical to think about light as a wave, spread out over a certain area, but then is only measured at one point. But that is only because you think about classical waves. The mathematics of QM is consistent, so why call it illogical? Well, it is a scientific fact that QM makes predictions that do not allow for local hidden variables. Until now these predictions are confirmed. This is a stronger statement than 'we are not able to detect potential local hidden variables'; it says 'we have proven there are none'. Well, you can tell them that indeterminism does not help. If people think that their free will lies in the disconnectedness of their action actions and thoughts, or the random character of their thoughts, they clearly have not thought deep enough.

We can't know what. I propose you open a thread in the QT forum under physics to see why is this. I am not a professional physicist. No, of course this is not proven. It is only proven that the statistical distribution is always the same. I also propose to discuss this in the QT forum. I think you have some real problems understanding (or accepting...) QT. No!! Why doesn't this go into your head? If QT predicts that the chance of a photon arriving is close to 100% in a certain area, then why do you say simply it can arrive anywhere. And in the double split experiment, a photon simply does not arrive at the dark stripes: QT predicts a statistical chance of zero. So what is this with an 'event can be present everywhere'? No. Bohm's theory, while conceptually possible, can impossibly be empirically proven: we cannot observe the complete universe, adding up the influence of all particles in the universe. Relativity already makes this impossible. And you forget: it is proven there are no local causes. That's great, at least something we agree upon. But then, still, why are you interested in knowing if people believe in determinism or not?

I more or less reacted on this in my previous posting. You seem to think that a bit of indeterminism means 'no determinism at all'. A photon arriving at a screen in a double split experiment is determined to arrive at certain places: but not exactly at which place. Take many billions of photons, and on repeated doing the experiment, you will always get the same interference pattern. No idea what you are talking about. You did not mention 'correlation' before. Not quite. It is also based on the experimental proof that local causes are ruled out. Non-local causes are, well, spooky. And I do not see that even with spooky, non-local, causes an experiment can be done that proves that there are non-local causes. I have no idea what such an experiment would look like. That is what Einstein thought. He turned out to be wrong. So is your interest in if we are determinists or not really fed by thoughts about free will?