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

#211

Post by GuB-42 » Tue, Jul 20, 2021, 11:11 PM UTC

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.

Isn't it the non-local hidden variable model? The idea that if local hidden variables do do not explain Bell inequalities, make the hidden variables non-local.

I think this model kind of works and some scientists are working on it, but it is not the preferred interpretation.

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

#212

Post by lisper » Tue, Jul 20, 2021, 11:13 PM UTC

feoren wrote: post #132

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…

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.

> I don't get why reflection isn't an observation/interaction there either.

I know this comment is going to get lost in the noise, but that is a really excellent point, one of the best that has been raised here so far. This is a point that is often glossed over, but it is actually really important, and quite challenging to explain without getting deep into the weeds. The answer is that passing through a half-silvered mirror is an observation/interaction, but it is special because it can be practically reversed by using additional mirrors so that you can get back to a state where you can no longer tell what the outcome of the "measurement" was. All measurements are reversible in principle, but some are irreversible in practice because the number of things you'd have to reverse is just too large. And in particular, by the time a measurement has affected the state of any macroscopic system (like a ball) it is absolutely impossible to reverse in practice, though not in principle. This process of becoming irreversible-in-practice is called "decoherence".

See [1] for a more detailed explanation.

[1] http://blog.rongarret.info/2014/10/parallel-universes-and-ar...

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

#213

Post by danbruc » Tue, Jul 20, 2021, 11:19 PM UTC

tbabb wrote: post #200

danbruc wrote: post #187

Earlier quoted context omitted.

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 evolutio…

The distinction between "adding" and "removing" a postulate is an important, non-arbitrary one. The "worlds" are there in both theories; Copenhagen adds a new phenomenon (non-unitary evolution) which makes some of them disappear at unspecified times. The "worlds" are direct consequences of suppositions shared with Copenhagen . Many worlds has N postulates, Copenhagen has no fewer than N+1. One theory is a strict subs…

I think it is not as simple as counting the number of postulates. The ultimate arbiter is physical reality and that decides whether removing or adding postulates is what brings you into agreement. The fact that the quantum state in some equation before wave function collapse looks like many worlds say nothing whether you should take this at face value or whether you are missing an additional postulate that gives you only one world.

If you argue that the collapse postulate is stupid because it is non-unitary and therefore in conflict with experimental evidence, then sure, I totally agree with this. But just because it is an additional postulate it does not per se make many worlds the better theory. Relativity without the constant speed of light is also a theory with one fewer postulate but it of course in much worse agreement with reality.

The problem with the interpretations is that we are currently unable to distinguish them experimentally which unfortunately adds much more personal preferences to the discussion then there should be.

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

#214

Post by Tomminn » Tue, Jul 20, 2021, 11:21 PM UTC

tylerhou wrote: post #20

lisper wrote: post #13

Earlier quoted context omitted.

That's not a bad analogy, but you have to be very careful here because no classical analogy can be a perfect fit for entanglement. The wave function is deeply and fundamentally different than our classical reality, and there is no way to reproduce its behavior classically. Among the fundamental differences is the fact that classical information can be copied but quantum states cannot be cloned. This is IMHO the singl…

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…

If you wanted to make this quantum, one is red and the other is blue only if you're looking for a red ball when you stick your hand in the bag. If you're looking for a purple ball when you stick your hand in the bag, then one is purple and the other is green.

That's the spooky part.

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

#215

Post by serverholic » Tue, Jul 20, 2021, 11:26 PM UTC

Kranar wrote: post #210

unparagoned wrote: post #203

Earlier quoted context omitted.

The analogy is fine for explaining entanglement. Sure it's more complicated when you consider superposition.

Entanglement is only applicable when there is a superposition of conjugate pairs. Without it, there is literally no entanglement whatsoever.

Please tell me you aren’t always this autistic

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

#216

Post by phscguy » Tue, Jul 20, 2021, 11:28 PM UTC

tylerhou wrote: post #20

lisper wrote: post #13

Earlier quoted context omitted.

That's not a bad analogy, but you have to be very careful here because no classical analogy can be a perfect fit for entanglement. The wave function is deeply and fundamentally different than our classical reality, and there is no way to reproduce its behavior classically. Among the fundamental differences is the fact that classical information can be copied but quantum states cannot be cloned. This is IMHO the singl…

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…

As others here have already noted, this analogy is wrong. But I think people here haven't given a convincing example of a system that behaves differently due to entanglement than it would if the behaviour were simply conditionally random (the ball example behaves identically if the balls are entangled or otherwise just classically random). The issue in finding a good example is that the effect of entanglement is rather subtle and hard to interpret intuitively.

Here is an example that may make it more obvious:

There exists a game that can be played cooperatively between two players that share two random bits. It is possible to win this game only 75% of the time if the bits are not entangled. If the bits are entangled there is a strategy for winning the game about 85% of the time. The details of the game and a good explanation can be found here: https://www.scottaaronson.com/blog/?p=2464

Basically, there is a game that involves sharing two bits, if they are entangled, it can be won 85% of the time. If they are not entangled but otherwise random (like the red and blue ball example), it can be won only 75% of the time.

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

#217

Post by lazide » Tue, Jul 20, 2021, 11:38 PM UTC

UncleOxidant wrote: post #173

lazide wrote: post #159

Earlier quoted context omitted.

If a simulation exists, and there is evidence of it, then sure we could surmise that someone created the simulator - and would have some evidence of such? I think the parent poster was noting that it is a pretty fundamentally different argument than say, positing the existence of a creator, because we exist at all - and that said creator has certain specific requirements of us regarding what we do on Sundays, for ins…

> and that said creator has certain specific requirements Is that a requirement of every flavor of creationism? Actually, maybe I shouldn't use 'creationism' in this context because that's a loaded term with a lot of baggage at this point. What else to call a hypothesis that asserts there's some kind of intelligence behind the universe that we see? Simulationists would seem to fall into that broader category as would…

Well, there are Simulationists which start going on wild flights of fancy about what said simulation creator intended/created it for, which yeah would start going into that territory pretty quickly.

Seems like first you'd need to have some kind of falsifiable evidence that we were in a simulation first before jumping there? Plenty of folks trying to do that though, without falling into the first case.

Personally it seems to have little to no real impact on anything I care about one way or another, so filed in the 'cute but who cares' bin.

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

#218

Post by lazide » Tue, Jul 20, 2021, 11:39 PM UTC

bdamm wrote: post #178

lazide wrote: post #148

Earlier quoted context omitted.

Ah, but that’s the tough part - there IS a measurable difference in behavior of the universe between these two examples! (albeit hard to experimentally prove exists, but it has been!) They really are in a superposition, not just ‘not known’ until one is measured. Just like light was proven to (truly, actually) be both a light and a wave through the double slit experiments. It doesn’t feel right, but it is - and that…

It could also be that we simply don’t understand something about light phase, and that’s causing us to get confused about superpositions. After all, the experiments aren’t on single photons, they are on beams of photons.

Not sure if we're confusing threads here - double slit experiments have been run on single photons and the results are pretty conclusive. Even a single photon is a wave that interferes with itself.

I would expect similar here. Intuition is terrible at understanding what is going on at the atomic and smaller level, or anywhere relativistic anything is happening.

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

#219

Post by jussij » Tue, Jul 20, 2021, 11:39 PM UTC

Couldn't that 'hidden variable' be just another dimension?

So while those particles might have been separated in space by a large distance, on that fifth dimension they haven't moved and are still sitting side by side.

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

#220

Post by danbruc » Tue, Jul 20, 2021, 11:41 PM UTC

joe_the_user wrote: post #206

danbruc wrote: post #191

Earlier quoted context omitted.

If you are only worried about analyzing a specific quantum system, then yes, for most part the interpretation does probably not matter. But I think in general the differences are very important, especially as we do not understand quantum mechanics and different interpretations will direct future research in different directions. If you believe in Copenhagen, you will try to figure out how to reconcile unitary evoluti…

If you believe in Copenhagen, you will try to figure out how to reconcile unitary evolution with wave function collapse. This is saying the interpretations "exist". The interpretation like intermediate values in some calculation process that are never returned. If the interpretations are true, they can be seen, not just "locally". It seems like a lot of this basically involves people who've "suspended disbelief" prov…

I am not really sure what you are trying to say. Are you talking about the difference between an interpretation as a way of thinking about something and an interpretation as describing what something really is?

It's like people who accept that general relativity specifies curved space, understand the implications but are still expecting to somehow find a higher dimensional space that all this is suspended in 'cause that's what a fundamental reality feels like to them.

General relativity works just fine without an embedding space but there still could be one. Not that you should think about it in this way without good reasons but only because it is more intuitive. But in the case of quantum mechanics we do - at least that is what I think - understand things so poorly that it is hard to judge what one should reasonably consider while making contact with questions about the fundamental nature of things.