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If we take two balls that change colours white and black, if we set that change in colours is always opposite one from another, for sure if we take one ball to the end of universe, if that ball will have black colour and second will have white colour..

How we know that spin (black and white balls) are not set from start when two entangled photos are made?

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Norbert Schuch
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user78495162
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    "Two entanglement photons are set in opposite polarization when leave crystal,so for sure they will keep this "synchronization" for ever..." is not true, they are called entangled for a reason. – jd27 Sep 30 '23 at 07:59
  • @jd27 So they dont leave crystal with opposite polarization? – user78495162 Sep 30 '23 at 08:03
  • the hazard of thinking about colored balls is that black and white are the only basis states, and they don't live in a Hilbert space. Nevertheless, I saw Gell-Mann do it, in person. – JEB Sep 30 '23 at 08:13
  • Of course that argument was made decades ago, and for the most part it was experimentally disproven (see for example Aspect's experiments). That's the point of entanglement. Assuming that "colors" are defined from the start boils down to assuming hidden variables. See Bell's inequalities. – Miyase Sep 30 '23 at 08:28
  • @Miyase How we know that spin/polarization are not set from start when two entangled photos are made? – user78495162 Sep 30 '23 at 08:55
  • That's the point of Bell's inequalities: there are measurable differences depending on whether the parameter is set from the start or not. I wrote that name in my comment so that you could check those out. – Miyase Sep 30 '23 at 10:08
  • @Miyase But physically he did not take into account the effect of indistinguishable particles. Hence, the premises of Bell's derivation are not complete enough for a description of the quantum reality. After Bell's theorem is refuted, we can no longer conclude that nature is non-local. – user78495162 Sep 30 '23 at 10:12
  • I don't know what you read about Bell's inequalities, but there's a large body of work going strong to this day, and numerous experimental tests with positive results. At this point in time, you really can't say that they've been "refuted". – Miyase Sep 30 '23 at 10:19
  • @Miyase so you dont believe in superdeterminism? – user78495162 Sep 30 '23 at 10:21
  • I don't even know what that is. I'm a physicist, studied and worked a lot on quantum mechanics, but I make a strong separation between, on one side, formalism and experimental results and, on other side, philosophical debates on the nature of physical laws. Both are interesting, but the latter cannot be allowed to influence the former (except as a source of inspiration, maybe). There was nothing in your question that hinted that it touched philosophical topics. – Miyase Sep 30 '23 at 10:24
  • @Miyase https://www.youtube.com/watch?v=ytyjgIyegDI – user78495162 Sep 30 '23 at 11:12
  • Thanks, but for this kind of topic, I'd much rather read a book written by an expert. I added this topic to my TODO list, out of curiosity. If it's scientifically relevent, I should be able to find a good book written by someone who also knows the physical aspects well too (although I have nothing against Sabine Hossenfelder, she makes good videos). – Miyase Sep 30 '23 at 14:28
  • @Miyase if first photon has always opposite spin from second one, it is not hard to conculde that they always show oposite spin,even they are separate bilions km ...i dont understand what is weird here?? – user78495162 Sep 30 '23 at 15:59
  • If you assume that photons have a defined spin from the start, then you're automatically in a situation without entanglement. So I fail to see how you're going to say anything useful about entanglement. But the comment section isn't the place for such an extended discussion, so I'll stop here. – Miyase Sep 30 '23 at 16:28
  • @JEB :"black and white are the only basis states, and they don't live in a Hilbert space" --- What about the Hilbert space spanned by black and white? – WillO Oct 07 '23 at 22:07
  • @WillO if they are on opposite sides of a Bloch sphere: fine. I'm just saying classical 2 state systems don't elucidate entanglement. Although Murray Gell Mann split 30 cents with Val Talegdi ...and then he walks across the room, and looks at his quarter and says "Val has a nickel"..there is no spooky action. Val was pissed. They argued constantly. – JEB Oct 08 '23 at 13:40

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What OP is suggesting is not entanglement. In OPs case the properties of both the particles that shoot in opposite direction is predefined albeit unknown to the observer due to lack of full knowlegde so to say.

Bell famously showed that one can experimentally test if thay is really the case in nature.

[Partly quoting from wikipedia] He showed that if measurements are performed independently on the two separated particles of an "entangled pair", then the assumption that the outcomes were predefined (also see Einstein–Podolsky–Rosen paradox) implies a mathematical constraint on how the outcomes of the two measurements (i.e., performed on each particle) are correlated. This constraint is called Bell inequality. Bell showed that quantum mechanics predicts correlations that violate this inequality.

In other words quantum mechanics (with its definition of entanglement) predicts a different correlation for the output of measurement then what one might expect from OPs proposal.

In addition experiments have shown that quantum mechanics description is correct. The 2022 Nobel prize was awarded for this verification.

S.G
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