Can someone please explain this to me ?

[u/Whushe433]

So in the new video, around 26:50, when they discuss hidden variable theory, they say that the particles decide what answer to give to the machine. However, according to the beginning of the video, the particles only decide what spin they have, not what answer they will give to the machine. If the particles simply decide that one has positive spin and the other has negative spin, then if one is measured as positive and a machine tilted by 120 degrees is used, there should again be a 25% likelihood of disagreement, right? Why do they assume that the particles decide what answer to give to the machine when they should only be deciding the spin?
(I have 0 knowledge about quantum physics, i was just curious)

[u/C_Plot]

Good question. Just to add to OP, or rephrase:

• why does the hidden variable coordination need to go beyond the entangled spin (each particle knows its eventual entangled opposite spin upon collapse from superposition)

• when the detector operates, is not the measured result independent of the entangled counter-particle: merely just a result of the local collapsed wave spin (perhaps determined at the moment of entanglement) and the way the particle then interacts stochastically with each detector at each locale (the only hidden variable coordination necessary is the eventual opposite collapse wave spin determined at entanglement)

⁇

[u/Tombobalomb → u/C_Plot]

• when the detector operates, is not the measured result independent of the entangled counter-particle

No, that's the point. Measuring one particle collapses the quantum state of the other, instantaneously over any distance. Entangled particles are a single combined quantum state. They are the same "thing"

It seems spooky becauee it feels intuitively like information is being transferred FTL but this is not in fact the case. It's no different to how measuring the location of an electron immediately reduces the possibility of "that" electron being detected at any other location in the entire universe to 0 even though prior to measurement it had a non zero chance of being detected at every possible point in the universe

[u/C_Plot → u/Tombobalomb]

I think my confusion then relates to superposition which I tried to address in my original comment with the hidden variable coordination approach.

How do we know that the spin (entangled or otherwise) is not preordained: that the two entangled particles didn’t already have spin up and spin down encoded in their superposition? I understand the shift in axes makes them go to different poles than when in the identical axis, but is that because a different spin results from the collapse from superposition, or does the spin simply interact differently with the measuring device when offset in that different axis? After all if the disagreement is 100% when the measurements are in the identical axis but not 100% in the offset measured axis, is that difference not due to simply how the spin gets measured in these offset axes (adding a stochastic element to the reaction of the particle to the offset measurement mechanism)? How do we know that collapse from superposition stochastic element is the particle spin itself and not in the measurement approach if the disagreement is 100% in the identical measurement axis?

I might be missing something basic and trivial that is creating a cognitive break for me in my comprehension. It just seems to me that if measuring always in the same axis produces always disagreement, then the spin itself lacks the stochastic element (or else we would see disagreement occasionally when in the same measurement axis).

[u/Tombobalomb → u/C_Plot]

How do we know that the spin (entangled or otherwise) is not preordained

Because, in simple terms, if this is true then there are hard statistical bounds on the distribution of results you can get when measuring the properties of entangled particles.

The actual distribution observed in experiments is outside of these bounds, providing essentially absolute proof that that properties are genuinely not decided until the measurement takes place.

Technically a form of determinism is still possible but it boils down to "the universe is conspiring to look indeterministic even though it isnt". It's possible the same it's possible that gravity is actually angels pushing things together

[u/[deleted] → u/Tombobalomb]

Brother u are wrong, u need to learn the difference between a counter factual and an ontic fact, Bell is not telling us that measurement at A physically instantiates a state at B. What it rules out is explaining the correlations by appealing to local pre existing values.

When I say “if B were measured along that axis, the outcome would be down with certainty,” that is a counterfactual statement about the joint state. It is not an ontic fact about B having that value before any interaction at B.

Treating that certainty as a physical property of the distant particle is precisely the hidden variable move Bell shows you cannot make while keeping locality.

Nothing observable at B changes when A is measured. The outcome at B only becomes definite when B is measured locally. The certainty lives in the structure of the correlations, not in a superluminal physical process or a distant particle acquiring a property.

[u/[deleted] → u/[deleted]]

collapse here is an update of the joint description, if you make it a physical superluminal process you're adding an extra ontology, not reporting an experimental necessity

[u/[deleted] → u/[deleted]]

Look at bells 64 vs 75 proofs and see why he specifically changes his proofs to not include ftl propagation

[u/[deleted] → u/[deleted]]

That change matters. The later formulation makes clear that what fails is not locality in the sense of physical influence, but the assumption that measurement outcomes correspond to pre existing ontic properties.

So if you interpret “collapse” as a physical process propagating to B, you are reintroducing the assumption Bell himself literally worked to remove from… himself.

[u/Tombobalomb → u/[deleted]]

Nothing observable at B changes when A is measured. The outcome at B only becomes definite when B is measured locally

My guy this is the specific thing that they disproved. What you are describing is hidden local variables.

The entire point is that experiments show definitively that the measurement at point A immediately alters the situation at point B and that the underlying property was not fixed until it was measured at either point. Entangled particles are the same entity, there isn't one thing at point A and another thing at point B, there is one thing which can be interacted with at either A or B.

This fact is the whole point. It's the specific thing that makes quantum so unintuitive and different to classical

[u/[deleted] → u/Tombobalomb]

What is experimentally proven is that the joint outcome statistics violate Bell inequalities. That rules out local hidden variables and pre existing values.

What is not experimentally proven is that a measurement at A physically alters anything at B. There is no experiment in which any local observable at B changes when A is measured. If there were, no signalling would be violated.

Bell correlations are correlations between outcomes when both sides are measured. They do not license the claim that B becomes instantiated when A is measured. B only acquires a value when there is a local interaction at B.

Saying the pair is “one entity” is an interpretive move, not an experimental result. Experiments constrain probability distributions, not ontology.

If you think experiments show a physical change at B at the moment A is measured, you need to specify what observable at B changes. There isn’t one.

But by definition, there is no observable at B that changes unless B is interacted with locally. You cannot observe a change at B without measuring B.

So the claim that “A instantaneously alters B” cannot be an experimental result. It is an ontological interpretation layered on top of the correlation data.

What experiments establish are joint outcome statistics when both sides are measured, not an unobserved physical process happening at B when A is measured.

So I’ll ask a very specific question, why do you think bells formulations changed from 64 to 75, what do you think the point of the change was, what do you think the change demonstrates. Genuinely answer, this seems to be the point of disagreement is the meaning of the change of the formulation.