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Chinese scientists test quantum entanglement over unprecedented distance

scientificamerican.com

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Re: Chinese scientists test quantum entanglement over unprecedented distance

#71

Post by dragonwriter »

novalis78 wrote: post #40
lucozade wrote: post #37

Earlier quoted context omitted.

With quantum entanglement, what happens to one particle prior to measurement affects the other even if the effect occurred after they were parted. That's where it gets really spooky. To belabour the colours and boxes analogy: We have 2 balls, if one is orange the other is always purple and vice versa. Now these balls have an extra property. If you shake them vigorously they may or may not change colour randomly. So,…

Sounds like they never were two separate entities to begin with or never parted location. Which is spooky too, in a different way.

> Sounds like they never were two separate entities to begin with

“Separate entities” may just be an artifact of intelligences trying to divide sense data about the universe into chunks they are capable of processing.

Re: Chinese scientists test quantum entanglement over unprecedented distance

#72

Post by Atwood »

heimdall wrote: post #17
sliken wrote: post #6

A staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destination. By my understanding that's impossible, although I always wondered if you could coordinate FTL, by detecting when a particle was no longer entangled. Can someone with the background comment?

Caveat: I only have a B.Science degree in Engineering Physics (Colorado, USA) and hobbyist-type research in PhD-level physics. I've always found it easier to explain quantum entanglement thusly: Imagine you have 2 cubes that alternate glowing between purple and orange. And they stay in one color for a random amount of time (100s of milliseconds). Holding both in your hands, you would just have randomly color-shifting…

Boojums All the Way through http://www.cambridge.org/catalogue/catalogue.asp?isbn=052138...

Re: Chinese scientists test quantum entanglement over unprecedented distance

#73

Post by indolering »

pishpash wrote: post #52
indolering wrote: post #30

Earlier quoted context omitted.

Damn, all of these explanations are overly complex! The most basic reason it doesn't work is because measuring your particle breaks the entanglement. So you would know that your partner has the opposite spin (or whatever) but you can't bootstrap any sort of communication system with that.

Not overly complex, but overly simple. I wish people talking about physics learn for the last time that analogies are a horrible way to explain a complex concept that at best adds an unnecessary translation layer increasing cognitive load and at worst hand waves away the most critical parts.

They just get too excited : )

Re: Chinese scientists test quantum entanglement over unprecedented distance

#74

Post by indolering »

EGreg wrote: post #68
Strilanc wrote: post #59

Earlier quoted context omitted.

How? You can't just keep measuring the position of the particle and keep a list. Recording quantum information entangles the recorder and the system under test, which affects how interference plays out, which affects the later parts of the path in a way that makes your path-computer not work.

How? Think a bit harder. It's pretty obvious once you get it. John Titor explained it to me last year. I'm just kidding. Yeah, what you said makes sense. How do we know though that IN PRINCIPLE we can't figure out which QM interprtation is correct? Because we are sure there is no additional data/math that can be developed?

I'm pretty sure you are just mistaken in that assertion. There are experiments we could do that would validate it ... but it allows for FTL communications and thus breaks causality. It might be like string theory in that there are extensions which you can't rule out....

Bohmian Mechanics is a pretty garbage theory, it was literally invented as a way to show that the math could be done in a certain way. It's only been of interest to fringe theorists and in pop-science venues because it preserves notions of discrete/continuous space in exchange for violating causality. It might be easier to imagine time-travel than throw away human notions of physical reality, but the universe doesn't care about our puny brains : )

Re: Chinese scientists test quantum entanglement over unprecedented distance

#75

Post by greeneggs »

MrZongle2 wrote: post #50
greeneggs wrote: post #46

Earlier quoted context omitted.

> A staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destination. Of course this is complete nonsense. It's useful for plotting stories, but seems to have imprinted on a large fraction of readers a total falsehood. Do you know where the idea started? I think the first time I saw it was in Orson Scott Card's novel "En…

Looks like it may have started in 1966 with a story by Ursula K. Le Guin. She called the device an ansible , which is what it was also called in OSC's books. https://en.wikipedia.org/wiki/Ansible

According to that Wikipedia page, Le Guin's ansible might not be relying on entanglement.

It "doesn't involve radio waves, or any form of energy. The principle it works on, the constant of simultaneity, is analogous in some ways to gravity ... One point has to be fixed, on a planet of certain mass, but the other end is portable."

About Card's ansible, it says, "Card's description of the ansible's functions in Xenocide involves a fictional subatomic particle, the philote. In the "Enderverse", the two quarks inside a pi meson can be separated by an arbitrary distance while remaining connected by "philotic rays"."

So perhaps Card's "Xenocide" (1991) is where the entanglement => FTL communication myth began?

Re: Chinese scientists test quantum entanglement over unprecedented distance

#76

Post by EGreg »

indolering wrote: post #74
EGreg wrote: post #68

Earlier quoted context omitted.

How? Think a bit harder. It's pretty obvious once you get it. John Titor explained it to me last year. I'm just kidding. Yeah, what you said makes sense. How do we know though that IN PRINCIPLE we can't figure out which QM interprtation is correct? Because we are sure there is no additional data/math that can be developed?

I'm pretty sure you are just mistaken in that assertion. There are experiments we could do that would validate it ... but it allows for FTL communications and thus breaks causality. It might be like string theory in that there are extensions which you can't rule out.... Bohmian Mechanics is a pretty garbage theory, it was literally invented as a way to show that the math could be done in a certain way. It's only been…

Right, well I can say the same about your intuition regarding causality and locality. Personally, I never thought that the locality requirement or speed of light limit was an absolute necessity. After all, you get spooky action at a distance either way. In fact, I would submit that avoiding pilot wave theory doesn't rid you of the possibility of non-locality. It might still be the case and now you have even more baggage.

Frankly, it's much easier for me to imagine a particle traveling along a pilot wave, and non-local events, then to imagine the world splitting into an infinite number of possibilities at every instance and everything being entangled with everything else in infinite to the third power set of possibilities.

By the way, is this an accurate overview? https://youtu.be/rbRVnC92sMs

Re: Chinese scientists test quantum entanglement over unprecedented distance

#77

Post by EGreg »

EGreg wrote: post #76
indolering wrote: post #74

Earlier quoted context omitted.

I'm pretty sure you are just mistaken in that assertion. There are experiments we could do that would validate it ... but it allows for FTL communications and thus breaks causality. It might be like string theory in that there are extensions which you can't rule out.... Bohmian Mechanics is a pretty garbage theory, it was literally invented as a way to show that the math could be done in a certain way. It's only been…

Right, well I can say the same about your intuition regarding causality and locality. Personally, I never thought that the locality requirement or speed of light limit was an absolute necessity. After all, you get spooky action at a distance either way. In fact, I would submit that avoiding pilot wave theory doesn't rid you of the possibility of non-locality. It might still be the case and now you have even more bagg…

Also https://www.quantamagazine.org/pilot-wave-theory-gains-exper...

Re: Chinese scientists test quantum entanglement over unprecedented distance

#78

Post by RugnirViking »

yorwba wrote: post #62
RugnirViking wrote: post #53

Earlier quoted context omitted.

Isn't that no better than a one-time pad if you need a classic channel?

Quantum key-exchange solves the distribution problem for one-time pads. And a one-time pad is the best security you could possibly get, so I'm not sure what you mean by "no better", since that's a given.

If you need a classical channel doesn't that just create another distribution problem though?

And yeah, but im considering one time pad as good as the security of its key in transfer

Re: Chinese scientists test quantum entanglement over unprecedented distance

#79

Post by darkerside »

lucozade wrote: post #45
darkerside wrote: post #42

Earlier quoted context omitted.

What is the equivalent to "shaking" in QM? I'm trying to figure out why it matters whether you shake the box or not (i.e. could the shaking simply not have an effect if you're not looking?)

The shaking represents any sort of action that doesn't perform a measurement. It was the first thing I thought of that could affect the ball without opening the box. It could be that the shaking didn't have an effect. But equally, it could have had an effect. The spooky bit is that the other ball 'knows' whether it did or not in a non-local way.

But isn't it possible that performing "shaking" might not affect any "ball" when it's "inside of a box"?

Re: Chinese scientists test quantum entanglement over unprecedented distance

#80

Post by indolering »

EGreg wrote: post #76
indolering wrote: post #74

Earlier quoted context omitted.

I'm pretty sure you are just mistaken in that assertion. There are experiments we could do that would validate it ... but it allows for FTL communications and thus breaks causality. It might be like string theory in that there are extensions which you can't rule out.... Bohmian Mechanics is a pretty garbage theory, it was literally invented as a way to show that the math could be done in a certain way. It's only been…

Right, well I can say the same about your intuition regarding causality and locality. Personally, I never thought that the locality requirement or speed of light limit was an absolute necessity. After all, you get spooky action at a distance either way. In fact, I would submit that avoiding pilot wave theory doesn't rid you of the possibility of non-locality. It might still be the case and now you have even more bagg…

> Personally, I never thought that the locality requirement or speed of light limit was an absolute necessity.

The only thing weirder than wave/particle dualism is violating causality.

> Frankly, it's much easier for me to imagine a particle traveling along a pilot wave, and non-local events...

Yup, that's why pilot wave theory is a hot topic in pop-science. You can totally imagine Marty McFly traveling back in time, that doesn't mean it would work.

I'm now entering tricky territory as I usually walk through this stuff with an actual physicist, but I don't have one one hand. So with the disclaimer that the following thought experiment is subtly incorrect [0].

We conceptualize things as either continuous or discrete. Take a solid block of matter and across the surface it is continuous. Break the matter in half and you now have two discrete units. If you keep breaking the matter in half, the conceptualization of a continuous/discrete has to break down.

So when you get rid of discrete space, is it really that weird when two "particles" seemingly "interact" when separated by ... space? Now trash the idea that time has discrete units and suddenly it's not that weird when particles "interact" across what we perceive to be discrete units of time.

The discrete/continuous paradigm is an artificial mental model that we impose based on our sensory inputs. That model is incorrect and you have to replace it with really complex metaphors derived from observing the behavior of these particles in experiments. From all the weird stuff we see in Quantum mechanics, we've never experienced FTL communication ... which is why Pilot Wave theory isn't taken seriously.

> then to imagine the world splitting into an infinite number of possibilities at every instance

The multiverse theory is a bullshit cop-out.

> By the way, is this an accurate overview? https://youtu.be/rbRVnC92sMs

Probably not, I stopped when they said that a particle travels all paths simultaneously. That's not correct, a particle does not exist in all places at the same time.

0: I'm pretty sure that the conceptual metaphors above still make use of global hidden variables....

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