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How Bell’s Theorem proved ‘spooky action at a distance’ is real

quantamagazine.org

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Re: How Bell’s Theorem proved ‘spooky action at a distance’ is real

#71

Post by jfengel »

lisper wrote: post #18

Note that there is a very important property of entangled particles that is hardly ever mentioned in this kind of exposition, which IMHO casts a lot of light on what is really going on, and that is that entangled particles do not self-interfere the way non-entangled particles do. For more details see: https://flownet.com/ron/QM.pdf

I don't think the paper justifies the statement as you put it, though perhaps you can point out what I'm missing. I don't think you can tell just from looking at the particle itself whether it has an entangled partner somewhere in the universe.

It is, however, possible to use the entangled partners to create systems with decidedly counter-intuitive properties that change the way the un-involved partner interacts. That's also the essence of Bell's Theorem.

It only works when you're controlling the experiment as a whole and thus not transmitting information faster than light... though you can set up the experiment in a way that makes the conventional transmission of information incredibly obscure. Bell's Theorem requires you to jump through a lot of hoops to exactly mimic that, which is why it took a long time to definitively rule out other interpretations of the experiments.

Re: How Bell’s Theorem proved ‘spooky action at a distance’ is real

#72

Post by Retric »

0majors wrote: post #62
drcode wrote: post #34

Earlier quoted context omitted.

Imagine you have a pouch with a red and a blue marble in it, then take out a marble without looking at it and hand the pouch to a friend. Later, if you look at your marble, you instantly have information about the other marble at a speed greater than the speed of light... but you couldn't use that fact to send a message. The only difference in quantum physics is that there are actually two parallel universes: One in…

That’s not quite correct. There are no good analogies between classical objects like marbles or socks and entanglement. In fact, Bell’s inequality was stated as a collaboration game that can only succeed if you use entangled particles. No classical object will get you the same results. You still can’t communicate faster than light but the reason is more subtle. The article does a good job but for a deeper explanation…

All analogies are flawed because the underlying reality is different. They can still be useful if they can communicate some more abstract idea.

An analogy I like for entanglement is to picture two atoms that will both decay at the same time. You could place them on other sides of the planet and until one is observed to decay nobody learns anything because the timing is unpredictable. After the observation people agree with that timing independent of distance but can’t communicate anything because the timing was random. Still, having two people both knowing some fact at the same time which can’t be observed by outsiders is a useful in it’s own way.

What I like about this is it’s clear what’s going on is different from what’s being described, it’s describing a property of something, and it separates information from communication. On the other hand it’s got plenty of it’s own problems.

Re: How Bell’s Theorem proved ‘spooky action at a distance’ is real

#73

Post by Gunax »

I've been posting this explaination for more than 10 years now:

http://www.felderbooks.com/papers/bell.html

I think I prefer Felder's explaination more than Quanta's. It's omitting some details (eg. the angles) but is better at explaining the difficulties of Bell's Inequality--why it seems like spooky action at a distance and why it cannot be used for communication.

Re: How Bell’s Theorem proved ‘spooky action at a distance’ is real

#74

Post by morpheos137 »

drcode wrote: post #34
nsxwolf wrote: post #27

I'll never understand entanglement. Every explanation makes me wonder why it can't be used to instantaneously send a message. I never fully understand the explanations why it can't be used to do so. I don't understand how you can be sure about the state of the other particle, what if someone already measured it and then did something to it?

Imagine you have a pouch with a red and a blue marble in it, then take out a marble without looking at it and hand the pouch to a friend. Later, if you look at your marble, you instantly have information about the other marble at a speed greater than the speed of light... but you couldn't use that fact to send a message. The only difference in quantum physics is that there are actually two parallel universes: One in…

Personally I prefer the superdeterminism arguement: i.e. the state of every "future" entanglement was already set "before" the big bang. The anthropocentric corollary is that "free will" is an illusion.

Re: How Bell’s Theorem proved ‘spooky action at a distance’ is real

#75

Post by morpheos137 »

TheOtherHobbes wrote: post #69
drcode wrote: post #34

Earlier quoted context omitted.

Imagine you have a pouch with a red and a blue marble in it, then take out a marble without looking at it and hand the pouch to a friend. Later, if you look at your marble, you instantly have information about the other marble at a speed greater than the speed of light... but you couldn't use that fact to send a message. The only difference in quantum physics is that there are actually two parallel universes: One in…

The only difference is that in QM the marbles don't really exist until you look at them. Somehow they still manage to align themselves so if one person sees red the other sees blue. Although it's even more accurate to say that if one person sees [colour] the other person sees [opposite colour]. The colours are random, but the relationship between them is fixed. Very crudely (and rather misleadingly but never mind) th…

>we have no idea where it is.

It is probably encoded in the cosmic horizon a la Green's Theorem.

Re: How Bell’s Theorem proved ‘spooky action at a distance’ is real

#76

Post by choeger »

Does the article do justice to the hidden variables hypothesis?

In case of the hidden variables, the spin is a (3-dimensional?) value that is identified by the measurement result. In case of quantum theory we have have a probability distribution. How is that probability distribution different from a hidden variables, except that it's not a straight number but a function instead?

Speaking as a programmer, is the difference between hidden variables and quantum mechanics that the former postulate a real-valued property whereas the latter speak of something like a monad?

Re: How Bell’s Theorem proved ‘spooky action at a distance’ is real

#77

Post by nikhilgk »

Kranar wrote: post #46
tylerhou wrote: post #20

Earlier quoted context omitted.

A classical analogy for entanglement: suppose I have two balls in a bag. They are identical in every way, except one is red and the other is blue. I randomly grab one in each hand and show my hands closed. Now the states of the ball are entangled: as soon as you see the color of one ball, that "determines" the color of the other. (Not claiming that this is a perfect analogy, but I don't see where it diverges from how…

>They are identical in every way, except one is red and the other is blue. I randomly grab one in each hand and show my hands closed. Now the states of the ball are entangled: as soon as you see the color of one ball, that "determines" the color of the other. This gets used to explain entanglement but it really has absolutely nothing to do with it. This is nothing that the ancient Greeks wouldn't have known. Not to p…

> This gets used to explain entanglement but it really has absolutely nothing to do with it. This is nothing that the ancient Greeks wouldn't have known.

To be fair, this usually crops up in entanglement discussions to deomonstrate how it can't be used for FTL communication and not to actually explain what entanglement is.

Re: How Bell’s Theorem proved ‘spooky action at a distance’ is real

#78

Post by 6gvONxR4sf7o »

choeger wrote: post #76

Does the article do justice to the hidden variables hypothesis? In case of the hidden variables, the spin is a (3-dimensional?) value that is identified by the measurement result. In case of quantum theory we have have a probability distribution. How is that probability distribution different from a hidden variables, except that it's not a straight number but a function instead? Speaking as a programmer, is the diffe…

Speaking as a lay person, I think the difference might be that it's specifically about local hidden variables. If two particles are coupled, there's no per-particle hidden variable?

Re: How Bell’s Theorem proved ‘spooky action at a distance’ is real

#79

Post by blueplanet200 »

choeger wrote: post #76

Does the article do justice to the hidden variables hypothesis? In case of the hidden variables, the spin is a (3-dimensional?) value that is identified by the measurement result. In case of quantum theory we have have a probability distribution. How is that probability distribution different from a hidden variables, except that it's not a straight number but a function instead? Speaking as a programmer, is the diffe…

I think Einstein would've considered nonlocal hidden variables the same as spooky action at a distance.

>How is that probability distribution different from a hidden variables, except that it's not a straight number but a function instead?

Because for entangled particles (separated by a large distance! but also any entangled particle) their PDFs will be correlated in a way that is impossible to define for just a single particle. This makes physicists uncomfortable because of relativity and things happening faster than light.

Re: How Bell’s Theorem proved ‘spooky action at a distance’ is real

#80

Post by blueplanet200 »

nsxwolf wrote: post #27

I'll never understand entanglement. Every explanation makes me wonder why it can't be used to instantaneously send a message. I never fully understand the explanations why it can't be used to do so. I don't understand how you can be sure about the state of the other particle, what if someone already measured it and then did something to it?

You can measure a particle's spin to be up or down. But you can't choose to measure it to be up. It's random and up to nature. This is exactly why it can't be used to send information.
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