So that's called "hidden variable theory". We've done tests that show it's not true. Basically, there are certain measurements you can do on entangled particles where you can prove each measurement is affecting the other measurement.

These tests you are referring to, are they a recent discovery? There is a long repeated misconception that violations of Bell's theorem has shown hidden variable theories to be false. If that's what you're referring to, then no we haven't. If, on the other hand, there's been some developments in the last 5 or 10 years, then it's very likely I've missed those.

If you are referring to violations of Bell's theorem, then what they show is that hidden variables are incompatible with locality. In other words, non-local hidden variable theories are compatible with these violations and have not been shown to be false.

The whole point is to show that something non-local is happening (or an equivalent), so of course I'm talking about local hidden variables. I don't understand your objection.

I'm being a little loose about casualty but that's because I don't want to write extra paragraphs about what "simultaneous" means.

You said "So that's called "hidden variable theory". We've done tests that show it's not true". But that claim is not true — hidden variable theory hasn’t been shown to be false, but local hidden variable theories have been.

In your latest comment, you say that "The whole point is to show that something non-local is happening". I'm not sure what thing's "whole point" you're referring to, but I suspect in the context of our conversation you're talking about the "whole point" of the implications of violations of Bell's inequality. But in that case, it's also not true that the point is that "something non-local is happening". There are QM interpretations that are entirely local, and compatible with the observed violations of Bell's inequality.

I found this paper to be a helpful breakdown of how the matter might be resolved, with some views embracing locality, and some rejecting it (some parts of the paper went over my head): https://arxiv.org/abs/1503.06413

> You said "So that's called "hidden variable theory". We've done tests that show it's not true". But that claim is not true — hidden variable theory hasn’t been shown to be false, but local hidden variable theories have been.

People usually assume locality. I was talking about local hidden variable theory.

I was using unclear language to say something true, which is different from saying something false.

> There are QM interpretations that are entirely local, and compatible with the observed violations of Bell's inequality.

They are either breaking locality or doing something equivalent. This is getting into metaphysics, not physics, isn't it? Unless a conversation is deep into the weeds of quantum physics, I feel comfortable making answers that assume a particular commonplace interpretation.

> They are either breaking locality or doing something equivalent. This is getting into metaphysics, not physics, isn't it?

We probably are into metaphysics. We're talking here about different theories that are all compatible with observations to date. Theory selection is very much a philosophical pursuit, though it's something physicists will do to.

Anyway, my main claim is that, as I understand it, the most popular or common QM interpretation (Copenhagen) embraces locality, so it's incorrect to say that "They are either breaking locality or doing something equivalent".

Here's an example of that from an article by Reinhard Werner ('What Maudlin replied to'), arguing (as I understand him) for locality. Some particles are entangled, separated, and then one particle is changed so as to impact (via entanglement) the other. However, the change on one to the other isn't real until later. "The state change only becomes effective when the results from the two labs are brought together and are jointly analyzed, which can happen centuries later."

In the other paper I linked you to, it has the realists (such as hidden variable theories) rejecting locality, with the operationalists (which, as I understand it, is the most common view) embracing it.

Sounds like the physicists maybe mixed up the concepts of correlation and causality.

Mixed up in what way?

Note that if you have two observers a light-second apart, and they only choose what measurement to do 0.01 seconds before performing it, at least one of those choices affects both results.

Using your analogy, you don’t put the legos in opposite orientation and walk away with one, it’s more like the two legos keep spinning and you walk away with one and you stop it from spinning and instantaneously the other one stops in the opposite direction.

What does “instantaneously” mean if we (afaiu) can’t even have “simultaneously” in general?

Aiui, it doesn’t at all matter which one is measured “first”, or if the two measurements are spacelike separated such that which one is first depends on frame of reference.

Whenever the two measurements are made, they will be correlated in a certain way.

You cannot communicate information from one to the other via how you choose to measure them, but you can in some cases coordinate on how your actions are correlated by choosing how to measure based on some info learned on one side.

So, if the direction along which A chooses to measure the spin depends on something A learned after A and B went far away from each-other, this can’t change the probabilities of B getting a result of 0 or 1, but it can change the probabilities of things like “A and B both get 1” or “A gets 1 and B gets 0”, etc. , even though not in a way that changes how likely it is for A to get 1, nor how likely for B to get 1.

This could conceivably be useful if uh, how useful it is for both parties to do something vs only one party doing it, changes based on the info, I guess?

All that pops into my head here, is that in this case, the two particles, when twinned, are actually the same particle... simply at different time references.

This behaviour makes zero sense to me otherwise.

That makes me think that all particles are actually the same particle, and we're only observing them at different time references. The twinning only objectifies that, so as observers, we are viewing them at time references which allow for known state.

Yes, this has a gazillion holes in it.

edit: to add to this, there is no reason to infer that because things are separated by distance, they are not the same thing. The universe does not have to play nice, to ensure that humanly derived, evolved logic thinks that things make sense from a classical perspective.

If all electrons, for example, are the same electron? Just observed at different time references and locations? Then things such as entanglement make more sense.

edit2: What I mean by 'the same particle', is that theoretically all matter in the universe was one ball of whatever prior to the big bang. Everything already is one particle, prior to diffusion and differentiation due to cooling.

Thus, every electron in the universe was at one point in time the same, single thing. Therefore, they are the same thing. If time does not exist, it means that this electron here, and over there, can be the same electron, for it can spend <unlimited time> here, and then <unlimited time> there, while at the same moment co-spanning the same time reference as we view it.

OK, I'll shut up now, because this is gibberish.

>That makes me think that all particles are actually the same particle

This sounds similar to Quantum Field Theory[1], which might interest you. I won't try to summarise it here because I don't have a good grasp on it myself, as a layperson (with a below-average understanding of physics, realistically!)

1: https://en.wikipedia.org/wiki/Quantum_field_theory

Thanks I shall poke at this.

Its... weirder than that. The issue is that the measurement of the particle changes it - and changes the entangled particle.

PBS Space Time - Quantum Entanglement and the Great Bohr-Einstein Debate https://youtu.be/tafGL02EUOA (and then watch the referenced Veritasium video)

The way they are linked is that each particle (in this case lego) actually has no orientation until you measure it, it's in a quantum superposition. But the 2 legos are guaranteed to have opposite orientations. One lego has orientation x, the other has !x

> until you measure it, it's in a quantum superposition

I assume it's been proved that it's in superposition, rather than in a static state? If so, how? Wouldn't knowing require measuring?

Or, maybe to make myself more productive, what's a good search term for this? :)

Bell's Theorem and the many experiments that followed allegedly prove that they couldn't have taken on any state before measurement, based on probability theory. If they had predetermined states before you measured them, there is a limit to how often an experiment could yield a certain result. But in these experiments, that limit is exceeded.

Search for "bell inequality".

There are reliable ways to create superposition particles: when you measure in one direction, the other direction is a superposition (https://physics.stackexchange.com/questions/43974/how-can-we...). I have no idea how to create entangled superposition particles: maybe read https://www.eurekalert.org/news-releases/473741.

You can tell the particles are in a superposition because they behave differently than those in a static state:

- Double-split experiment: https://en.wikipedia.org/wiki/Double-slit_experiment - only particles in a superposition create interference patterns

- Bell's paradox: https://www.youtube.com/watch?v=v7jctqKsUMA, https://www.youtube.com/watch?v=hiyKxhETXd8 - entangled particles in a superposition can be measured to make predictions with more confidence than if they were simply static particles with different states

I guess a good search term would be "Polarized light and quantum mechanics" because IMO polarized light is a good example which you can even simulate yourself if you have a polarizing filter (https://www.youtube.com/watch?v=zcqZHYo7ONs&t=736s, https://www.youtube.com/watch?v=ZudziPffS9E, https://chem.libretexts.org/Bookshelves/Physical_and_Theoret...)

The polarised one is really crazy as it is macroscopic and daily life.

It's also dead easy to do - use a cheap laser pointer, a tinfoil cap with a pinhole, and some polarising lenses from an optician (he gave me a couple for free).

This is also my question/confusion.

You're describing a Hidden Variable Theory, which does not work https://en.wikipedia.org/wiki/Hidden-variable_theory

Local hidden variable theories are ruled out by Bell's Theorem. Not hidden variable theories in general. I realise GP was describing a local HVT, but it's still an important distinction.

Sure it can. Bell's theorem implies you can have locality or hidden variables, but not both. de Broglie-Bohm is an example of a non-local hidden-variable theory.