This part is incorrect. The original particle does not have a known spin, zero or otherwise. It is simply a thing not measured.and that the particle-pair comes from an original single particle with spin zero — tim wood
The particle does not have angular momentum. Spin in quantum theory is not a measurement of its rotation, a classical concept meaningful only to something with extension. It just means that they send the particle through a pair of charged plates and it is deflected one way or the other, never not at all, and always the same magnitude of deflection. This has been dubbed 'spin', but the word has nothing to do with the classical meaning of the word.The sum of the angular momentum of the two must then always be zero. — tim wood
That assumption should not be made. I'm pretty sure it can be falsified. It's a counterfactual assumption, and I'm not sure how counterfactual interpretations describe the state before measurement.It is a simple step to assume that before the measurement, the particle really has a determinate spin value that the detector measures. — tim wood
Indeed! But I will quibble with you. In what sense do you suppose I do not understand the theorem, against what I do claim to understand about it? I recognize spin and entanglement in this context as terms of art and do not pretend to understand them - nor do I think anyone does understand them. And Bell was able to express and make clear just how mysterious some of the results of experiments are by showing that two mathematical descriptions, one seeming incontrovertible and the other making accurate predictions, were inconsistent. I get it, the referral to a specialist forum, but too often the content, as with a forum we're both familiar with, is not worth the candle. But if you can enlighten my darkness here, please go ahead!with an often poor attempt to convert it into language. — Philosophim
Indeed! But I will quibble with you. In what sense do you suppose I do not understand the theorem, against what I do claim to understand about it? — tim wood
So you have a mathematical expression of a limit, and a mathematical description that accurately predicts the actual outcomes, and they're inconsistent with each other. And alas, there's no more than that to it. — tim wood
The Bell inequality constitutes an explicit prediction of the outcome of an experiment. The rules of quantum mechanics can be employed to predict the results of the same experiment. I shall not give the details of how the prediction is derived from the mathematical formalism of the quantum theory; it can be stated, however, that the procedure is completely explicit and is objective in the sense that anyone applying the rules correctly will get the same result. Surprisingly, the predictions of quantum mechanics differ from those of the local realistic theories. In particular, quantum mechanics predicts that for some choices of the axes A, B and C the Bell inequality is violated, so that there are more A+ B+ pairs of protons than there are A+C+ and B+ C+ pairs combined. Thus local realistic theories and quantum mechanics are in direct conflict. — Scientific American
And certainly not like the spin of a billiard ball or a basketball. My own opinion is that both spin and entanglement are defined as a kind of behavior of particles. I.e., if they behave that way, then they have spin and are entangled, and if they have spin and are entangled then they behave that way. I am unaware of anything more substantive than that, though I'm sure more is said. — tim wood
the popular explanations of things just seem always to leave out some critical step or detail. — tim wood
The speed of light as speed limit is what is sacrificed, but with an interesting qualification: that the particles “communicate” instantaneously, but that no message can be sent using entanglement. — tim wood
This confuses me. What does it mean that communication takes place instantaneously but no information can be transmitted? I would have thought that "communication" means the transfer of information. I have to do more reading
At the moment, to borrow an inequality, I would say that my understanding is now less than or equal to yours. I looked at Bell's paper long ago, but the math was too much, and I too ignorant. He works it out in three dimensions as I recall. So, whatever comment you care to make and whenever you care to make it, I'll be more than glad to read it.I'm going to take a look at Bell's original paper and see what I find. That may take a while. — T Clark
I think it works like this: Alice is on earth and Bob on a spaceship near Arcturus about 37 light years' distant, monitoring his particle detector. Its bell rings and Bob sees that it registers "up." What information does that convey to him? Ans. none. — tim wood
Different because the respective spins are not limited to opposites. — tim wood
So you have a mathematical expression of a limit, and a mathematical description that accurately predicts the actual outcomes, and they're inconsistent with each other. And alas, there's no more than that to it. — tim wood
if you've tried and struggled to understand it, I definitely recommend at least one go of the above article. It took some effort but it really clarified everything for me. — flannel jesus
The implications of those results are a bit harder to get a grip on - What do they say about realism and locality? — T Clark
Sure, I thought the article maybe did a good job at explaining that but perhaps it's not as explicit as it could be. I'm only a layman, but I do have what I consider to be a relatively compelling analogy, if you're interested. — flannel jesus
Quantum measurements are indeterminate prior to measurement, genuinely and actually indeterminate rather than just a question that we don't yet have the answer to. Ontologically indeterminate, if you will. Bells theorem settles that question pretty cleanly, which is why it's so valuable in the history of quantum mechanics. — flannel jesus
Hi and thank you! I've read it, without yet doing the hard work of it, and I don't yet understand the second part of it. I think I have a general understanding of Bell's attack, in that he worked out the math of the probabilities, which I could not follow, having to be satisfied with the dumbed down version, and the inequality itself. So think I pretty get both sides. What comes after that is interpretation/speculation, and these are beyond Bell's theorem.I've found this article to be the most straight forwardly comprehensible explanation of bells theorem.... I will say I think you've done bells theorem a little bit of a disservice here. — flannel jesus
...the results have nothing definitive to say about QM interpretations.... Except you'll find people who disagree with that. The whole many earth's interpretation was developed to address that issue. Reality is a metaphysical characteristic, not a scientific one. — T Clark
"When certain elementary particles move through a magnetic field, they are deflected in a manner that suggests they have the properties of little magnets. In the classical world, a charged, spinning object has magnetic properties that are very much like those exhibited by these elementary particles. Physicists love analogies, so they described the elementary particles too in terms of their 'spin.'
"Unfortunately, the analogy breaks down, and we have come to realize that it is misleading to conjure up an image of the electron as a small spinning object. Instead we have learned simply to accept the observed fact that the electron is deflected by magnetic fields. If one insists on the image of a spinning object, then real paradoxes arise; unlike a tossed softball, for instance, the spin of an electron never changes, and it has only two possible orientations. In addition, the very notion that electrons and protons are solid 'objects' that can 'rotate' in space is itself difficult to sustain, given what we know about the rules of quantum mechanics. The term 'spin,' however, still remains." — tim wood
May I know what you were drinking before you wrote your post? I should like to try some for those occasions when I too would like to loosen my grip on reality. — tim wood
Just as I said, the so-called "spin" is not a property of a particle at all. The 3-d geometrical representation which is called "spin" cannot be the property of a non-dimensional point. — Metaphysician Undercover
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