How Bell’s Theorem proved ‘spooky action at a distance’ is real • Hacker News Board

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

#81

Post by dane-pgp » Tue, Jul 20, 2021, 6:31 PM UTC

themgt wrote: post #16

nobodyandproud wrote: post #11

Earlier quoted context omitted.

Those objections to super determinism seem weak, or more along the lines of “I don’t like the implications, so I won’t consider it.” Genuine question: Would quantum computers work in any deterministic framework?

I've quoted it before but I will again just because I hate superdeterminism so much: First, the logical flow: Bell’s theorem proves that no local, realistic theory can reproduce the predictions of quantum mechanics. It does so by considering a very specific situation of entangled particles being measured by spin detectors set at different angles. Critically, the angles of these spin detectors are assumed to be set in…

> I would be tempted to call these people philosophically desperate.

Wouldn't it be equally valid to say that the Quora commenter is philosophically desperate to avoid the natural conclusion that there is an entity that is able to influence the actions of Newton and Caesar etc. and the commenter themselves?

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

#82

Post by lisper » Tue, Jul 20, 2021, 6:32 PM UTC

jfengel wrote: post #71

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. Tha…

See section 4.2, and in particular the paragraph that starts "Here's the kicker..."

It is true that you can't tell if a single particle is entangled or not. But if you have an ensemble of particles all prepared in the same state then you can tell if that state is entangled or not. Non-entangled (a.k.a. pure) states have a preferred basis that produce self-interference. Entangled (a.k.a.) mixed states do not.

(The pure-mixed dichotomy is a little misleading because it depends on your point of view. A single member of an EPR pair is in a mixed state, but the pair as a whole is in a pure state.)

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

#83

Post by 0majors » Tue, Jul 20, 2021, 6:35 PM UTC

Retric wrote: post #72

0majors wrote: post #62

Earlier quoted context omitted.

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 agre…

The problem with that analogy is it gives an illusion of understanding while being completely misleading about what Bell’s inequality actually tells us about nature.

The whole point of Bell’s inequality is that quantum entanglement is fundamentally different than classical correlation between two objects which have some opposite properties the observer simply does not know about before observing one of them.

It’s not helpful to use an analogy which teaches the reader the exact opposite of the point you are trying to make.

Your example with decaying atoms suffers from the same misunderstanding. Quantum entanglement is not about lack of information about some specific states, if that was the case, why would anyone talk about loss of locality?

Understanding entanglement and Bell’s inequality requires a completely different ontology than your everyday experience with classical objects. I highly recommend the video I linked above for an approachable explanation. It is not as simple as these analogies but at least it gets to the actual point of this result which tells us something profound about how nature works.

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

#84

Post by mensetmanusman » Tue, Jul 20, 2021, 6:35 PM UTC

morpheos137 wrote: post #74

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…

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.

The universe seems to have surely went to great lengths to trick its own atoms into believing they have free will. :)

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

#85

Post by 725686 » Tue, Jul 20, 2021, 6:37 PM UTC

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?

Funny, I never understood how you could possibly send a message using entanglement. Try to explain how would you do it, and either you will understand why it can't be done... or earn a Nobel prize. Win-Win.

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

#86

Post by tsimionescu » Tue, Jul 20, 2021, 6:40 PM UTC

tylerhou wrote: post #52

tsimionescu wrote: post #39

Earlier quoted context omitted.

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…

Bell's inequality (as you allude to) describes how transformations on quantum wave functions cannot behave classically. But classical wave functions can certainly be entangled as entanglement is a property of a wave function, not transformations on wave functions.

I'm not sure what you mean by classical wave functions - I've only seen the term 'wave function' used for quantum mechanics. Are you referring to classical wave equations? I'm not sure how the concept of entanglement is supposed to apply to classical waves though.

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

#87

Post by morpheos137 » Tue, Jul 20, 2021, 6:41 PM UTC

mensetmanusman wrote: post #84

morpheos137 wrote: post #74

Earlier quoted context omitted.

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.

The universe seems to have surely went to great lengths to trick its own atoms into believing they have free will. :)

I don't know what you mean. The number of atoms involved in the free will delusion is infintesimal compared to the number of atoms in the universe.

Number of atoms in 8 billion human brains:

about 10^35

number of atoms in the universe

about 10^82

according to search results.

Maybe there are no aliens but homo sapiens are just the first stage of the universe becoming self aware.

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

#88

Post by normac2 » Tue, Jul 20, 2021, 6:43 PM UTC

Retric wrote: post #72

0majors wrote: post #62

Earlier quoted context omitted.

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 agre…

You describe that as an analogy, but I always took that to be what it actually is (or at least one very simple example). Are you saying that that is how we interpret our experience intuitively, but we need a more radical account under the various mainstream interpretations of quantum physics (Many Worlds, Copenhagen, etc.)?

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

#89

Post by codezero » Tue, Jul 20, 2021, 6:51 PM UTC

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?

It's easy to understand (I'm being a bit hyperbolic) if you can believe that space and time are emergent properties of matter and not required for the underlying physics.

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

#90

Post by abetusk » Tue, Jul 20, 2021, 6:53 PM UTC

abetusk wrote: post #53

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?

Let's say particles have a 'direction angle' that we can measure with a detector that only gives 'up' or 'down' relative to a direction angle measurement. We can change this direction angle measurement with a knob to set what the measured 'up' and 'down' answers are relative to the detector's direction angle. Further let's say particles can be quantum entangled so that when when two detectors are placed very far apar…

I see, I actually answered the wrong question, sorry about that.

I'm also a bit confused by why it can't be used to send information but here's a try:

In the above scenario, if the particle (pair) has completely random spin, one that can only be observed by detection and not by some sort of construction, then each observer sees a completely random bit, regardless of whether it gets "flipped" by the "non-local" observation/communication of the other particle. They'll only be able to discover the correlation after the fact, if they compare notes and thus have to meet up, destroying any non-local benefit.

Put another way, if you have a bit with probability p of being 1 ((1-p) of being 0) that you're communicating over the wire but the wire is so noisy as to flip it with probability 1/2, then you won't be able to recover what the transmitted information was.

You'll be able to discover the correlation between the bits if you compare notes after the fact but since the "wire" acts as a completely noisy channel, you can't recover the transmitted bit.