Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

quantamagazine.org

Post reply on HN
Print view View original

181–190 of 356 posts

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

#181

Post by tylerhou »

lisper wrote: post #155
serverholic wrote: post #146

Earlier quoted context omitted.

You didn't add anything to his example. This is just purely to be pedantic.

No. The only way you can actually observe entanglement is in an isolated entangled system (this is the reason quantum computers are hard to build). It is true that at a philosophical level there is no difference, but from the point of view of physics , which is to say, what is observable , isolation is crucial. Non-isolated systems behave classically, notwithstanding that they are actually quantum systems.

Would you claim that when Einstein developed his theories of relativity, they were invalid (from the point of view of physics) because their consequences were not yet observable? For example, Einstein used thought experiments to develop special relativity in 1905, but since kinematic time dilation was only experimentally confirmed in 1971, his work was not a contribution to physics until then?

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

#182

Post by void_mint »

qwerty456127 wrote: post #179

How long is it going to take until we can have a near-zero-latency Internet connection on Mars (e.g. on a Mars rover) or Moon?

At the speed of light, it would take between 4 minutes and 14 minutes to travel between Mars and Earth. A quick google says fiber optic cable can transfer data at roughly 70% of that speed. It may not be possible to get the latency you're describing. Mars is far away.

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

#183

Post by ithkuil »

tylerhou wrote: post #171
sawalk4 wrote: post #140

Earlier quoted context omitted.

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…

> By saying ahead of time, "one ball is red, the other is blue", you're describing a hidden-variables theory of entanglement. No, consider the case of neutral pion decay, which emits one spin up electron and one spin down electron. We can clearly say ahead of time one electron will be spin up, and the other will be spin down. But there is no hidden variable that determines which. If there were a hidden variable, then…

This a good source for learning this stuff for real instead of pop-sci approximations:

https://ocw.mit.edu/courses/physics/8-04-quantum-physics-i-s...

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

#184

Post by dw-im-here »

ericb wrote: post #3

If we were in a simulation, would the speed of light be the processing speed of the universe as each area re-renders, and spooky action at a distance be two variables pointed to the same memory location, populated with a lazy-loaded value, with copy-on-write semantics? edit: seems like it is lazy loaded, so revised my summary.

no

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

#185

Post by mr_gibbins »

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…

No, I'm sorry, I'm not going to pull out heaps of regurgitated quantum information to back this up but that's straight-up wrong.

The red ball and the blue ball exist as physical objects, it is us, the observers, who are unaware of whether they are red or blue at either position. There's no superposition here. They are red, or blue, assigned randomly. Not both, not none. These are facts - properties - about the balls that are real, that exist, but we simply don't have that information at that point. It is meaningless that there is no observer that can 'see through' our hands to know which is correct.

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

#186

Post by [deleted] »

Kranar wrote: post #157
feoren wrote: post #130

Earlier quoted context omitted.

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…

OPs explanation is that entanglement is when there is a red ball and a blue ball and when you know which ball is red, you determine that the other ball must be blue. My explanation is that entanglement is when there is no red ball or blue ball, there are simply two balls and the color of both balls is both red and blue simultaneously. It's not simply that one ball is red, the other is blue, but we don't know which on…

[deleted]

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

#187

Post by danbruc »

tbabb wrote: post #153
danbruc wrote: post #138

Earlier quoted context omitted.

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,…

it actually introduces many worlds No, this is the misunderstanding that I'm talking about. The extra "worlds" follow directly and exclusively from the existence of the various basis states in a wave function, and the laws of entanglement. No other postulates are needed. Before the measurement/entanglement, the system and environment are independent, and can be written (|0> + |1>) ⊗ (|0> + |1>). After the entanglemen…

The extra "worlds" follow directly and exclusively from the existence of the various basis states in a wave function, and the laws of entanglement. No other postulates are needed.

The many worlds are in the entangled state but then the collapse postulate reduces them to one world. If you remove the collapse postulate you put them back in. And sure, the collapse postulate is an awful solution breaking unitary evolution and you have every right to reject it, but that does not change the fact that many world introduces - or at least not removes - additional worlds that are not there in Copenhagen.

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

#188

Post by 6gvONxR4sf7o »

6gvONxR4sf7o wrote: post #78
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?

edit-too-late-to-edit: I remembered something that makes me think it's actually more complicated.

If I write 0 and 1 on two different pieces of paper, then flip a coin to decide which paper to give you, we have "entangled" unknowns. When I reveal my paper, we instantly know what's on yours. The joint distribution can't be described per-particle, but we don't consider it spooky. So I think there's something more to it.

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

#189

Post by gus_massa »

lisper wrote: post #143
gus_massa wrote: post #122

Earlier quoted context omitted.

I agree with the GP. If you only have a single member of the pair, then you will see the same interference pattern in a double slit experiment than with a not-entangled particle. It doesn't matter if the other particle has collided with a brick, went thru a double slit experiment, went thru a bad double slit experiment, or is flying to Andromeda. (In spite that the calculation to get the correlation with any result i…

What can I say? You're wrong. The math shows that you're wrong (as does the elementary argument presented in the paper). Find a physicist and ask them if you don't believe me.

I have at least 8 Physicist that I email/zoom regularly (at least twice per month). I also have half a degree in Physics, with at least 2 courses of Quantum Mechanics (all the advanced courses also use QM, but there are 2 courses only about QM). [I also have a degree and a PhD in Math, but it's not too relevant here.]

Anyway, I'll read the article thoughtfully and write a long comment tomorrow. Can you take a look tomorrow?

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

#190

Post by uh_uh »

qwerty456127 wrote: post #179

How long is it going to take until we can have a near-zero-latency Internet connection on Mars (e.g. on a Mars rover) or Moon?

You can not use QM for faster-than-light communication: https://en.wikipedia.org/wiki/No-communication_theorem
Post reply on HN