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Quantum ‘spookiness’ passes toughest test yet

nature.com

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Re: Quantum ‘spookiness’ passes toughest test yet

#21

Post by skarap »

stefantalpalaru wrote: post #16
skarap wrote: post #11

Every time I read something on quantum theory I can't help but notice how close to notion of magic it feels like. And I've studied physics in college. Some time ago I thought how strange these all would look to someone who had no knowledge in physics at all. But then I got it: two particles in different galaxies being entangled is not much different from calling someone on the other side of the globe using a cellphon…

I see it as a failure of the model. When the explanation is irrational, does a scientist stop to wonder at the irrationality of the universe instead of trying to come up with better explanations?

While I agree that science is currently seeing only small part of the picture, I don't believe scientists have stopped trying to find explanations.

And what is more important - it's very hard to judge if the explanation is rational. Every science is built on some axioms which define what is rational and what is not. That's why I guess the progress happens step by step (each next step expanding what one would consider rational).

Re: Quantum ‘spookiness’ passes toughest test yet

#22

Post by jcr »

saurik wrote: post #2

FQXi (39 comments): https://news.ycombinator.com/item?id=10130203 Nature (1 comment) (same link as this one): https://news.ycombinator.com/item?id=10135260 Scientific American (0 comments): https://news.ycombinator.com/item?id=10139598 Ars Technica (0 comments): https://news.ycombinator.com/item?id=10141658 Forbes (0 comments): https://news.ycombinator.com/item?id=10129946

Thanks saurik, I somehow missed the fqxi.org article submission when searching before (re)submitting the nature.com article.

Re: Quantum ‘spookiness’ passes toughest test yet

#23

Post by dools »

jblow wrote: post #10
dools wrote: post #7

Earlier quoted context omitted.

What you've quoted there is a good analogy of an entangled state. In reality there are several differences, and the biggest piece of misinformation is that measurement of one system somehow "collapses a wave function" in the other system which isn't the case. The phenomenon of entanglement is that measurements of certain things are either perfectly correlated or anti-correlated. Eg. Measurement of spin along some axi…

I don't see how you can claim that the idea of wave function collapse here is a misunderstanding. The mathematical meaning of the statement "two things are entangled" is that you cannot factor the states into the product of two separate quantities. So there is only one equation for the two particles. So once you "collapse" this for one particle (whether or not collapse is a physical action) it is by necessity collaps…

Yes that's a good way of putting it. What I've seen around is talk that "measurement of one particle effects the other" and often people use the term "collapse the wave function of the other particle" to articulate this (because they'd heard the term). The fact that the entangled state of the 2 particles is described by the same wave function resolves this.

Re: Quantum ‘spookiness’ passes toughest test yet

#24

Post by dools »

coldtea wrote: post #9
dools wrote: post #7

Earlier quoted context omitted.

What you've quoted there is a good analogy of an entangled state. In reality there are several differences, and the biggest piece of misinformation is that measurement of one system somehow "collapses a wave function" in the other system which isn't the case. The phenomenon of entanglement is that measurements of certain things are either perfectly correlated or anti-correlated. Eg. Measurement of spin along some axi…

> The similarity to 2 coins is: if i have a 1972 coin and a 1973 coin, and give one to you randomly, then you go a million light years away and look at your coin and find you have the 1973 coin, you will know I have the 1972 coin. Although this is only a simplified analogy of entanglement the important point is that the state was prepared before we separated, and no information has been communicated. When you try to…

No what I'm describing is a way of understanding why entangled states aren't spooky. It's also a direct lift from Leonard Susskind so it's not even me doing it. The point is that the state is prepared in some way X, and the state is such that by knowing something about one thing, you also know something about the other thing.

The actual mechanism by which this occurs is only "spooky" if you try and interpret it classically. But if you just accept that "hey, it's quantum mechanics" then it's very easy to understand. Same as I can't visualise a 5-sphere but I have mathematical tools to work with one.

I can't "picture" the mechanism that allows measurements of quantum states to be anti-correlated, but I can use maths to express that behaviour and make predictions about how the universe behaves.

Re: Quantum ‘spookiness’ passes toughest test yet

#25

Post by dools »

ikeboy wrote: post #17
dools wrote: post #7

Earlier quoted context omitted.

What you've quoted there is a good analogy of an entangled state. In reality there are several differences, and the biggest piece of misinformation is that measurement of one system somehow "collapses a wave function" in the other system which isn't the case. The phenomenon of entanglement is that measurements of certain things are either perfectly correlated or anti-correlated. Eg. Measurement of spin along some axi…

The entire point of Bell's theorem is that there can't be something corresponding to "the state was prepared before we separated", because no local hidden variable theory can predict the same as QM predicts.

This is not local hidden variable theory. The measurement of one half of an entangled pair doesn't modify the probability distribution of the other half of an entangled pair. There is no modification, just a phenomenon unexplainable by classical physics whereby certain measurements on either system are either perfectly correlated or anti-correlated.

Re: Quantum ‘spookiness’ passes toughest test yet

#26

Post by dools »

sago wrote: post #15
z92 wrote: post #14

Earlier quoted context omitted.

The similarity to 2 coins is: if i have a 1972 coin and a 1973 coin What you have explained is "Quantum local hidden variable theory". Which has been proven wrong again and again. The article says this test has closed the last loopholes that made this theory a possibility. https://en.wikipedia.org/wiki/Local_hidden_variable_theory

You're misunderstanding his point, I think (or I'm being overly generous in interpreting him!). Though I admit he over-eggs it to a confusing degree. The two coins metaphor illustrates the anti-correlation of two particles and why that doesn't allow faster-than-light communication. By observing one, you can deduce the other. Of course it isn't a metaphor for the whole process, such that you can derive implications fr…

Yes that was my point.

Re: Quantum ‘spookiness’ passes toughest test yet

#27

Post by ikeboy »

dools wrote: post #25
ikeboy wrote: post #17

Earlier quoted context omitted.

The entire point of Bell's theorem is that there can't be something corresponding to "the state was prepared before we separated", because no local hidden variable theory can predict the same as QM predicts.

This is not local hidden variable theory. The measurement of one half of an entangled pair doesn't modify the probability distribution of the other half of an entangled pair. There is no modification, just a phenomenon unexplainable by classical physics whereby certain measurements on either system are either perfectly correlated or anti-correlated.

How are you saying "the state was prepared before we separated" without meaning a local hidden variable theory? The only way for that to make sort of sense would be superdeterminism, or a nonlocal HV theory, which is definitely not the consensus in QM.

>The measurement of one half of an entangled pair doesn't modify the probability distribution of the other half of an entangled pair.

That's just saying it's local. Not relevant.

Re: Quantum ‘spookiness’ passes toughest test yet

#28

Post by dools »

ikeboy wrote: post #27
dools wrote: post #25

Earlier quoted context omitted.

This is not local hidden variable theory. The measurement of one half of an entangled pair doesn't modify the probability distribution of the other half of an entangled pair. There is no modification, just a phenomenon unexplainable by classical physics whereby certain measurements on either system are either perfectly correlated or anti-correlated.

How are you saying "the state was prepared before we separated" without meaning a local hidden variable theory? The only way for that to make sort of sense would be superdeterminism, or a nonlocal HV theory, which is definitely not the consensus in QM. >The measurement of one half of an entangled pair doesn't modify the probability distribution of the other half of an entangled pair. That's just saying it's local. No…

The only way for that to make sort of sense would be superdeterminism, or a nonlocal HV theory, which is definitely not the consensus in QM.

The only for it to make sense classically. It doesn't need to make sense, it just is. It's how QM works, you can't understand it by some classical mechanism.

Basically this:

https://en.wikipedia.org/wiki/Hidden_variable_theory#Declara...

Re: Quantum ‘spookiness’ passes toughest test yet

#29

Post by coldtea »

dools wrote: post #24
coldtea wrote: post #9

Earlier quoted context omitted.

> The similarity to 2 coins is: if i have a 1972 coin and a 1973 coin, and give one to you randomly, then you go a million light years away and look at your coin and find you have the 1973 coin, you will know I have the 1972 coin. Although this is only a simplified analogy of entanglement the important point is that the state was prepared before we separated, and no information has been communicated. When you try to…

No what I'm describing is a way of understanding why entangled states aren't spooky. It's also a direct lift from Leonard Susskind so it's not even me doing it. The point is that the state is prepared in some way X, and the state is such that by knowing something about one thing, you also know something about the other thing. The actual mechanism by which this occurs is only "spooky" if you try and interpret it class…

>No what I'm describing is a way of understanding why entangled states aren't spooky.

I think that if the explanation doesn't also convey the spookiness, it's not right.

>The actual mechanism by which this occurs is only "spooky" if you try and interpret it classically. But if you just accept that "hey, it's quantum mechanics" then it's very easy to understand.

That's just pushing the spookiness under the carpet.

Re: Quantum ‘spookiness’ passes toughest test yet

#30

Post by ikeboy »

dools wrote: post #28
ikeboy wrote: post #27

Earlier quoted context omitted.

How are you saying "the state was prepared before we separated" without meaning a local hidden variable theory? The only way for that to make sort of sense would be superdeterminism, or a nonlocal HV theory, which is definitely not the consensus in QM. >The measurement of one half of an entangled pair doesn't modify the probability distribution of the other half of an entangled pair. That's just saying it's local. No…

The only way for that to make sort of sense would be superdeterminism, or a nonlocal HV theory, which is definitely not the consensus in QM. The only for it to make sense classically . It doesn't need to make sense, it just is. It's how QM works, you can't understand it by some classical mechanism. Basically this: https://en.wikipedia.org/wiki/Hidden_variable_theory#Declara...

You chose to use the phrase. If it doesn't make sense, don't use it. Saying "indeterminism" is fine.
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