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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

#131

Post by eigenket »

tick_tock_tick wrote: post #96
dvt wrote: post #12

Earlier quoted context omitted.

If we were in a simulation, it feels overzealous to make the assumption that the computing model would be anything at all like what've developed. Best assumptions you can make is that it follows some kind of consistent logic (though there's caveats here, too).

The speed of light is the exact kinda of constant a programmer would add to a system to solve problems.

But quantum mechanics is exactly the opposite of what a programmer would add. At least as far as we understand it is (exponentially) harder to simulate quantum systems than classical ones.

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

#132

Post by feoren »

tsimionescu wrote: post #39
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…

The problem with your classical analogy for entanglement is that it doesn't match the data. Or rather, it only matches the data for quantum properties that are similarly blue or red. The non-classical properties of entanglement start appearing once you start measuring combinations of the redness and blueness of those balls. Let's say that instead of looking at the balls, you pass them through some machine that will l…

This is a great thought experiment, thank you. I'm not totally clear how the machines could work without actually taking a measurement, though. It sounds like you're saying the 2nd machine (P = 0.5) takes measurements (and therefore "paints" the balls), but the other two don't?

I've heard of the apocryphal "half-silvered mirror", but I don't get why reflection isn't an observation/interaction there either.

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

#133

Post by naasking »

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?

> I'll never understand entanglement. Every explanation makes me wonder why it can't be used to instantaneously send a message.

Say you and Bob share a bunch of entangled particles. Bob wants to send you a message using those particles, so he takes one particle at a time and encodes his information. How would you know he did so? At the very least, Bob would still have to send you a classical signal to say he did something.

There are more subtle arguments why this doesn't work even at the particle level, but that at least should give you an idea why superluminal communication won't work.

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

#134

Post by jdb1729 »

Zamicol wrote: post #68

If you "measure" the bits per character in the base 45 alphanumeric encoding used in QR code, you'd get 5.5 bits per character as 11 bits is used for two characters. How is it possible to have information less than a bit, a partial bit? What is that ".5" part? Isn't a bit indivisible? Only in the context of a character doublet is all information expressed. To know the "half bit" part, you cannot "look" at just one ch…

5.5 bits is also the average information content of a single run of the GHZ experiment. In this setup three parties independently choose a binary detector setting and each observe a binary outcome. The first two parties observe an independent random bit regardless of their settings. If an odd number of the parties have their setting "on", then the third party also observes an independently random bit (6 bits total to record, 3 for the settings and 3 for the observations). But if an even number of of the three settings are "on", then the third party's observation is completely determined by the other 5 bits. When the settings are chosen randomly these two possibilities are equally likely so on average it takes 5.5 bits to record the results of the experiment.

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

#135

Post by feoren »

naasking wrote: post #126
UncleOxidant wrote: post #124

Earlier quoted context omitted.

It's kind of interesting how people who would never consider a creationist explanation seem quite willing to embrace the idea that we're in a simulation.

One is an assertion with no logic to justify it, the other is an assertion with a somewhat persuasive argument justifying it [1]. They are simply incomparable. [1] https://www.simulation-argument.com/simulation.html

Of the 3 assertions in the abstract, the obviously false one is #2: "Any posthuman civilization is extremely unlikely to run a significant number of simulations of their evolutionary history". When you realize that running a simulation of the universe requires more processing power than is available in the universe, this is very obviously false.

I respect people who believe in a bearded White omnipotent homophobic God who lives in a sky palace more than I respect people who believe in this insane drivel about the probability of living in a simulation. At least the former were indoctrinated as their brain was forming.

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

#136

Post by danbruc »

joe_the_user wrote: post #116
danbruc wrote: post #48

Earlier quoted context omitted.

The only difference in quantum physics is that there are actually two parallel universes: One in which you took out the red marble & one in which you took the blue one. You don't know what universe you're in until you look at the marble, but still it doesn't help you to transmit a message to your friend. I don't think it is helpful to talk about multiple universes, that makes a strong implication towards a many world…

I don't think it is helpful to talk about multiple universes, that makes a strong implication towards a many world interpretation. You're correct but the point is "many worlds" or Copenhagen interpretation having no implications , they each describe the same mathematical/experimental results. They're just "ways to think about the results". They matter as much as whether you label the axes of a graph x and y or A and…

Even if they have no observable differences, they still make different metaphysical claims. If I see Schrödinger's cat alive, many world claims that there actually also exists a dead cat while Copenhagen claims that there is only one alive cat. You may argue that the differences are irrelevant for all practical purposes but you don't get to claim that there are no differences between different interpretations.

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

#137

Post by mrkstu »

cma wrote: post #35
SV_BubbleTime wrote: post #14

Earlier quoted context omitted.

I could be WAY off, but if locality isn’t entirely true, and the “read success” is 33-67%, doesn’t that still leave quite a bit of wiggle room for communicating information in some fault tolerant method?

Correlations only but no useable communication. You can both make a decision on the same random info that isn't determined until later when you are apart, but can't know anything other than that if they followed the plan they made their choice based on the same later-determined random info, correlated with your random info. If they didn't follow the plan and measured orhogonal/same (can't remember which) spins, then…

If we agree before parting that one of us is going to Alpha Centari and the other is staying on Earth and going to assassinate either the President of Russia or America depending on the observed state on an entangled pair of particles, once I reach the star system.

Doesn't the traveler have more information than anyone else on ship about whether an assassination attempt was made in Russia or America? and have it faster than the speed of light? We don't have it with certainty, but we have shared knowledge that is unknowable to others and instantaneous.

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

#138

Post by danbruc »

tbabb wrote: post #91
danbruc wrote: post #48

Earlier quoted context omitted.

The only difference in quantum physics is that there are actually two parallel universes: One in which you took out the red marble & one in which you took the blue one. You don't know what universe you're in until you look at the marble, but still it doesn't help you to transmit a message to your friend. I don't think it is helpful to talk about multiple universes, that makes a strong implication towards a many world…

> that makes a strong implication towards a many world interpretation You say that like it's a shortcoming. :) There are many who take the (very reasonable) position that the many worlds interpretation is the most epistemologically parsimonious one. Contrary to some misunderstandings of it, it doesn't "add" extra worlds; it removes the concept of "wave function collapse", and leaves all the other known laws of quantu…

Contrary to some misunderstandings of it, it doesn't "add" extra worlds; it removes the concept of "wave function collapse", and leaves all the other known laws of quantum mechanics completely unchanged.

Yes, it gets rid of the collapse postulate, but no, it actually introduces many worlds. You can wiggle a bit around, claim that prior to the wave function collapse there are also many worlds in Copenhagen or whatnot, but in the end many worlds makes a metaphysical claim that two cats exist, one dead, one alive while Copenhagen claims only one cat exists in the end.

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

#139

Post by feoren »

tbabb wrote: post #91
danbruc wrote: post #48

Earlier quoted context omitted.

The only difference in quantum physics is that there are actually two parallel universes: One in which you took out the red marble & one in which you took the blue one. You don't know what universe you're in until you look at the marble, but still it doesn't help you to transmit a message to your friend. I don't think it is helpful to talk about multiple universes, that makes a strong implication towards a many world…

> that makes a strong implication towards a many world interpretation You say that like it's a shortcoming. :) There are many who take the (very reasonable) position that the many worlds interpretation is the most epistemologically parsimonious one. Contrary to some misunderstandings of it, it doesn't "add" extra worlds; it removes the concept of "wave function collapse", and leaves all the other known laws of quantu…

My understanding is that "Wave function collapse" is an artifact of one of the many possible ways of describing quantum mechanics mathematically. There's really nothing to remove, is there?

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

#140

Post by sawalk4 »

feoren wrote: post #130
Kranar wrote: post #66

Earlier quoted context omitted.

Fair enough we'll simply disagree on that. Entanglement is not a property about wave functions and really has nothing to do with waves. It's a logical consequence of the uncertainty principle and was ironically deduced by Einstein, Rosen, and Podolsky (EPR Paradox) as a way to argue that quantum mechanics is an incomplete description of physical reality. Being that it's strictly a consequence of the uncertainty princ…

While I believe that entanglement is genuinely something new and interesting, your explanation of it simply feels like a semantic difference. There is no way in which the universe you describe would be different from a classical universe, at least up to the limits of your description. I'm simply "not allowed" to say that one of the balls is red and the other is blue, before I've looked? It's just, what, against the l…

Isn't this distinction exactly what the article is about? By saying ahead of time, "one ball is red, the other is blue", you're describing a hidden-variables theory of entanglement. It may be unknowable (before measurement) which color the ball in your left hand is, but it has a color.

But Bell's theorem provides a very measureable counterexample to this type of explanation of entanglement. Sure, in the article they talk about electron spins instead of ball colors, but the analogy is that there isn't a well defined "color of the ball" before it's measured.

Of course, the analogy breaks down a bit: electron spin can be measured in multiple axes with somewhat complicated interactions.

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