Eise

Because I feel treated as a stupid moron here, I asked the question on another (German, sorry) physics forum. There, one of the moderators answered me in the following way. First he gave me link to this article, in which following phrases can be found (you can check if I have taken them out of context, but I do not believe so): After I explained Swansont's line of argument he reacted with the remark that one can say it like this (... the particle becomes spin down at the moment the other particle is measured), but that it is an unfortunate expression prone to lead to misunderstanding because it implies a wrong picture of what is happening. I also happily see that you changed 'determine' in 'precede'. That takes at least some of the misunderstanding away.

OK. I understand that. For the rest you are so short in your answers, that it does not help me to understand the points you are making. Maybe somebody else can explain this? How can we say that from one frame of reference event 1 determines event 2, but from another that event 2 determines event 1?

So Wikipedia is wrong here (hey, of course Wikipedia can be wrong, I know that). Italic and bold by me. If you think I am saying something differently let me know. Or correct the Wikipedia article. Or explain to me what the difference is between determining and causing. ('To determine' has a gross ambiguity: it can mean, in daily context, 'to find out, to ascertain', or 'to settle, to direct'. Maybe we should take care in what we mean here, because it seems as if in QM both meanings are practically the same...) Hmmmm. I think this is the point where we disagree. Classically you're surely right. I'll think over the rest of your post. I might come back at some points. That we do not know. The only thing we know is that the particles had no definite spin before the measurement of one of these particles: that is ruled out by Bell's theorem. What we do know is what we will measure if we already happen to know what was measured at detector 1. And there is a gap between these two, which we cannot fill up, even if we can make the gap as small as you want.

Did I suggest something else? This is tiresome, Swansont. I did not present this article as proof that that the other experiments are wrong or something. It shows that the correlations as predicted by QM are correct, even when viewed from different inertial frames. Right. I fully agree and never denied it. Somehow you seem to think I do. Right. I even agree with this. But the statement above is more general than the one you originally did: Let's try once again: detector 1 measures the spin of particle 1 as spin up detector 2 measures the spin of particle 2 as spin down From inertial frame A particle 1 is measured first: so according to you from that moment on the spin of particle 2 becomes spin down. This of course also means that it becomes spin down in front of detector 2. From inertial frame B particle 2 is measured first: so according to you from that moment on the spin of particle 1 becomes spin up. This of course also means that it becomes spin up in front of detector 1. This means that in a. the measurement of particle 1 determines the spin of particle 2, but in b. measurement 2 determines the spin of particle 1. In my eyes that makes no sense, as from both inertial frames we look at the same experiment. Therefore I conclude that the only thing we are justified to say is that the measurements are correlated, not that one determines the other. So, now instead of just saying I am wrong, or do not understand QM or Bell-experiments, say what my confusion is, and why clarification of this confusion leads to the justification of your statement that particle 2 becomes down when the measurement of particle 1 is measured up. I think I am pretty precise in why I think what I think, so I would appreciate it if you make some effort in showing where according to you my error lies.

Neither. See here. Hey, your the one who wants to get the Nobel prize for physics because you found a bad explanation of special relativity in the internet! Now I understand your question... You find BS everywhere.

No. I found one myself: Simply said: if the detectors are at nearly the same distance from the source, then an inertial frame can be found in which the order of detection can be opposite, then in the laboratory frame. So I have no idea how you can say what the moment is that particle 2 becomes spin down when the other one is measured. These are just tests of the violation of the Bell-inequalities by QM. That is not our discussion. Our discussion is the question if it is justified to say: (Bold by me) Given the experiment I linked to, even I was wrong: according to this experiment it is not even justified to say that the measurement of particle 1 determines from that moment on what the measurement of the particle 2 will be, because an inertial frame can be found in which the order of measurements was opposite. The only thing we can conclude is that the measurements are correlated, nothing more.

Please mention the experiment(s), with a link please.

I think you did, when you said that the spin of the particle becomes down. If you mean with 'becoming down' that 'will measure down from then on' I agree with you. Otherwise I do not. Exactly. But you cannot give an experimental setup, that justifies your statement that a single particle becomes spin down at the moment its entangled counterpart is measured. You can only say that from the moment its counterpart is measured having spin up, it is determined that it will be measured spin down.

Only if you know in what direction it was measured. If I send particles to you, one by one, and sometimes I measure their spin, sometimes I do, but I do not say in which direction I measured, you cannot distinguish between which particles I have measured, and which I didn't. So having a 'definite spin' is not intrinsically for the particle: it is at most intrinsically to the complete experimental setup. In EPR-like experiments, if I vary the distance of the particle source, I cannot decide on my measurements of particle 2 alone if I measured the spin first, or if the measurement of particle 1 was first. Even if I compare my list of measurements of particle 2 afterwards with the list of measurements of particle 1, I cannot decide which was measured first: I only see their correlation. If I cannot decide this, what sense does it make to speak of the moment one of the particles becomes spin down? No. It is only when comparing the measurements, that I can see that the measurements are correlated. And that this correlation is faster than light. But I cannot say when particle 2 became down. Only when particle 1 is measured first, I can say that this measurement determined the measurement of particle 2. That is an interesting point... But I must confess I have seriously troubles to understand your first paragraph, which is in fact one single sentence. I would be glad if you could formulate your point a bit more extensive and clear. (Really! I am glad somebody tries to understand where the confusion lies.) But on your second sentence: I think this 'determinate state' is context dependent. If I know that particle's 1 spin is measured vertically, and it is up, then I know, when I measure also in the vertical direction, that I will measure down. Is that what you mean with a determinate state? But then, when I don't know in what direction particle 1 was measured, how can I find out if particle 2 is in a determined state? What is a determined state when it is dependent on the measuring context? Swansont says I can find out by measuring many particles (which he forgot I already mentioned before), but that is not the point in EPR-like situations (if it was, and I was using photons, I could use my polaroid sunglasses to prove E, P and R were wrong...).

No. I am saying it makes no sense to talk about the moment that the spin of particle 2 becomes down. Which is inconsistent with QT, and why? Do you have empirical support for this?

I do not want to invent a new form of QM. I want to retract to the only point we can really know: that the measurements of particle 1 and particle 2 are correlated; that we cannot look behind the scenes of quantum measurements. I understand that, so I am not so clear where I say something that contradicts this. Maybe you can spell this out? In my opinion, the problem lies in the word 'determined'. If I measure particle 1, then I immediately know what a measurement of particle 1 will be (or has been, it could already have been measured before I measured mine. I can only know this if I compare lists of observations from measure station 1 and measure station 2). So, as I see it, Swansont (and you?) on one side, and I on the other, understand different things under 'determined'. Say, particle 1 is measured first, and its spin is up. - Then I say from that moment on I know what a future measurement on the spin of particle 2 will be: down. - Swansont says: at that moment the spin of particle 2 becomes down. I state that both are empirically equivalent, because any experiment to try to prove the second, implies a measurement. And that is exactly the first statement. The same holds for single particle measurements, as I described above. I try to translate this in English (Anton Zeilinger, Einsteins Spuk, page 208): Then he refers to Kochen and Specker. (BTW, the first possibility Zeilinger mentions is to give up locality. Zeilinger notices that this option is the most popular under physicists...) PS On reading about Zeilinger's professional work, I encountered (for the first time) the Leggett inequality. From Wikipedia:

Perhaps because you do not express yourself clearly enough to be understood? Where I always make a clear distinction between 'measuring of particle 1' and 'measuring of particle 2', you just say 'measurement'. Of course nature is not tricking us. If I measure the spin of one single particle (no EPR situation), and it is down, then it really was down at the moment of measurement. But to say it was therefore down all the time is an empirically empty statement. Now this measurement has a consequence: for every subsequent measurement, I know that I will measure spin down again and again. This suggests what you are stating all the time: that the particle has spin down after my first measurement. But what I am saying is that I only know that there is a 100% correlation between the measurements. To say that the particle has spin down means that an independent observer can determine its spin without knowing its measurement history. And that is impossible: if I don't know that it was measured vertically, there is no way I find out that it has spin down when measured vertically. So I can only conclude that the measurements correlate, but empirically there is nothing special with the particle for any independent observer. See? How can I answer such a question if you do not say which measurement in which situation? What is the operational definition of 'having a definite spin'? What upper bound of what delay? Which experiments? How do these experiments decide between 'a particle becoming spin down' and 'being sure that spin down will be measured'?

No. They are determinate. I only don't know which half is in which envelope. That is exactly the 'revolutionary' insight of the Bell-inequality: that no theory with local variables can reproduce the predictions of QM. And so even hidden variables won't do. In your example there are hidden local variables, so your explanation is worthless. Sorry for my anger, but I get tired of Swansont (and now you) thinking that I do not understand the Bell theorem and its consequences, only because I give a different interpretation then he does. Possibly you mix me up with the OP. I did not say one was a defence of the other. I am saying that it is the viewpoint I defend. Right. That means my viewpoint was valid all the time. Or the video is wrong, when it says: I already noticed that the key difference between us is what here is meant with 'once they are measured'. I interpret 'they' as plural, i.e. when both particles are measured. You say that the spin of one particle is measured, you know the spin of the other. But I see that as a logical consequence (because of the law of preservation of angular momentum), not as a measurement. Of course you can be sure as if you measured it directly, but you did not measure it. But you can be sure that if you measure the spin of particle 2, you will measure down, because you measured the other one up. So for all practical purposes, you can treat the particle as having spin down. But that does not mean it has spin down. But as said before, you go one step further: You seem to know when particle 2 becomes down. (Of course I know the particle did not have those spins from the beginning. (Really, you seem to think I am stupid)). But I don't know how you can know when the spin of particle 2 becomes down, if there is no way to empirically verify this. If I change the distance of my 'particle 2 measurement' device from the source, the only thing I will ever notice is that the measurements are correlated, nothing else. I know that. I thought you meant something else, but was not sure. The relevance for the topic is what Kris_o_O wrote here: My point is that one does not know if it is instantaneous. We only know that the measurements correlate, so if you measure the spin of particle 1, you know what a measurement of the spin of particle 2 will be (or was).

I did here: The video says at this point: So what is the difference? 'eliminate the particles having a definite spin before the measurement'? No idea what you mean. Can you please explain?

Yes, I know that and I understand that. But it seems you have only read my last sentence, and then you just say something we are not discussing. My point is that it is impossible to empirically distinguish between the situations where one measures the spin of particle 2 before or after the measurement of particle 1. That is the reason that I say that at the moment you measure particle 1, you know what will be measured at particle 2. That is a proposition that is independent of the order of measurements. Say I am the observer of particle 1, independently of exactly when you measured particle 2, I know you will have measured particle 2. Then you are not reading very well. Once again: The video says, literally: I defend this point, and you say I am wrong. If I am wrong, then the video is wrong, or at least not precise enough. E.g. one could change it as follows: ...it only makes sense to talk about spin once one of them is measured. Is that what you mean? OK, I understand that. So do you defend a hidden variable scenario? Or what do you mean by 'Even...'? OK. But AFAIK the experiments done in Bell-like situations show at least that there are no local hidden variables. And again you are unclear: you say the "particles' spins", and just 'measurement'. Do you mean I measure particle 1, and then the particles' spins are determined? And -BTW- by using the word 'determined' you introduce just another version of this unclarity: If you say that determined means that it is fixed that I will measure spin down at particle 2, I agree. If you say that determined means that the spin of particle 2 becomes down at the moment I measure spin up at particle 1, I do not agree, because there is no empirical way to find out when this happens. If I for example change the distance of my second measuring device, I just will always find the same correlation between measurements.

Especially this, from the article: That is what relativity is based on. So when Einstein says light speed is invariant he is wrong, but when you say it, it is correct???? And then suddenly all the argumentations of Einstein, based on the invariance of the speed of light are wrong???? And ehhh... why are you so angry, already in your first post?

But you are not explaining. Your posts here are nothing more than 'no you are wrong, I have studied physics, and it is like I say.' If I give a transcription of a part of the video, and I give an argument based on that transcription, but then only only say 'No, actually, it doesn't' but do not say why, it is not much help. This is what you said: Where are your particles 1 and 2? I think the ambiguity lies in 'the measurement'. So let me try to rephrase what you write above: a. There is 100% correlation of the spins, which are undetermined before the measurement of particle 1. Right, I understand that, with only this catch: there is 100% correlation between the measurements of the spins. b. If the particles had a pre-determined spin before the measurement, you would get different results. Right, that is what the Bell-inequality is all about. c. So in essence, particle 2 does become spin down when the other particle is measured to be spin up, because we know the specific spins could not have been in place before the measurements And this I do not understand. The part I do understand is what you said in b.: the spins are not determined before I measured particle 1. The part I do not understand is that you claim that at the moment I measure the spin of particle 1 being up, the spin of particle 2 becomes down. The reason is that I do not understand how you can know this. The only thing you know is that if you measure particle 2 in the same direction as particle 1, you will measure down. The reason I say this is, that you cannot empirically distinguish, based on your measurement of particle 2 alone: - if particle 1 was measured before you measured particle 2 - if particle 1 was measured after you measured particle 2 - if particle 1 was measured was measured at all If you cannot distinguish these, then what sense does it make to say that 'particle 2 does become spin down when the other particle is measured to be spin up', when there is no way to find out when this happens? Of course. But only one of the interpretations would suffice, isn't it? Both being correct interpretations is a kind of overkill. The problem I have with Swansont is that the video says: But then when I defend this position he says I am wrong. Can you help me out? Your remark between the brackets helps a little. But what is wrong, when I state more precisely that, after measuring particle 1, I know what spin I will measure with particle 2 in the same direction? What is the justification to say that it becomes spin down already before the measurement or particle 2?

I did not tell you what you believe: I wrote: 'If he is right...'. The maker of the video suggests that there are 2 possible interpretations: it only makes sense to talk about spin once they are measured entangled particles can signal each other faster than light to update their hidden information when the one is measured You told me the particle has a spin down as soon as the other is measured up: That excludes the first possibility. And it fits the second. Of course the particle has spin down at the moment it is measured spin down. But you said it already has spin down before you measured it, on basis of the measurement of the other. Yes, every followup measurement in the same direction will show us a spin down. But if you say that the particle already has spin down, before every subsequent measurement, you are going one step too far. Say, I measure the spin of just a single particle: it has spin down. Do you say then that it already had spin down before I measured it? Now it turns out, I was fooled: it was in fact an entangled particle. Laughing the other observer comes into the room, and says to me: 'I knew you would measure spin down, because I measured spin up.' Do you say now that it already had spin down before I measured it? But I was fooled again: the other particle was measured after I did my measurement. How does this change your position about the question of the particle already was spin down before you measured it? This citation is a literal transcription of the video: So I really do not understand you: you say that the spin becomes down at the moment the other particle is measured, but then you claim there is no hidden state before I measure the particle. A correction must be convincing. Maybe you are right, but then you did not explain it well enough. Can you show me where I make an error in my understanding of entanglement? Maybe that helps.

As you called this link as your 'wittness a decharge' (supposing I do not understand entanglement?), I carefully listened to this great explanation. See for yourself what phrases he uses: And last but not least: If he is right, then you belong to the second group, that obvious believes that hidden information is changed (faster than light!) because of the measurement of the first particle. Measuring real behaviour, means the spin is already there before it is measured, no? Isn't the 'revolutionary aspect' of QM that it shows that this 'assumption in science' is not correct?

Swansont, I think I understand what you mean, but I am inclined to formulate your last sentence differently: measuring the particle spin down means that if I measure it again in the same direction as before, I will measure down again. The italic part is important: if I ask you to measure the direction of the spin of a particle I give to you, but do not say in which direction I measured it, you have no way to find out that I measured spin down. Of course, if I give you thousands of particles, all measured down, you will find out: but not with one single particle.

Until here I follow you, assuming that you mean that the measurements of the spins correlate 100%. Otherwise you must explain this more detailed. And here I am not sure. QM says that the spin of a particle is not determined until it is measured. Now if you say that the spin becomes down you suggest it has a determined spin. What does that mean: that a local variable in the particle flipped to down? That makes no sense of course. As far as I can see the only thing you can say according to Bell's theorem is that the measurements are correlated, not the particle themselves. I know that sounds absurd, but if you formulate it in terms of the particles themselves, you make your self 'guilty of local variables-talk'.

Seasoned physicists correct me when I am wrong, but.... the spin of the other particle does not become spin down instantaneous. What Bell's theorem says is that when you measure the spin in a vertical direction you will measure spin down. That's it. All the rest is metaphysical speculation. There is no causal relationship between measuring one particle and the other. So we know there is no mechanism.

Would questions in a box do?

Me to. So let me repost what I have once written before: So, no, philosophy is not science, but it isn't 'fluff' either.

That is true. Two clocks, made according the same blueprint and exactly the same materials will be exactly alike. That means you will not care which clock you get, they will function exactly the same. Let's take your wife into the game: you are duplicated to Mars, 2 days later, you die on earth, but your wife doesn't know anything about it. Even worse, an hour after the duplicating she has phoned with your duplicate, and the duplicate says that everything went fine, he felt nothing of the whole process, and he wishes your wife a nice week, because you will return next week... with the teletransporter of course. At earth your wife welcomes you at the teletransporter gate, during your duplicate on his turn dies after two days on Mars in great pains. (Want to add some emotion...). Your wife is happy that your back, she notices no difference at all, you tell what you did on Mars, you remember the party where you both were 2 weeks before. Now here is the difference: for you the two clocks are the same, as long as you have one. For your wife, you your first duplicate and your second duplicate are exactly the same. So we are all happy. But for you, yourself: did you really die? Even twice? The difference is that for your there is another point of view: your experience of you being you. A clock has no inner experience. But if you believe that your are a brain process, and the brain process is exactly copied, you should believe that it doesn't matter in what piece of matter this process is running. Or you believe that your brain is something special, that is not copied to Mars. But then I want to know what this speciality of your present brain is. If you really believe that you are a process of your brain, then on Mars that other brain is then your brain. Where is the difference?