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Why quantum entanglement doesn't allow faster-than-light communication (2016)

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Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#111

Post by taeric »

drwiggly wrote: post #109
taeric wrote: post #67

Earlier quoted context omitted.

This is still a part that annoys me. I have asked why you can't use the correlations to facilitate communication, and people always seem to think I'm asking why you can't do this per particle. I get that the the individual measures are basically useless on their own. Question is if the correlations can be confirmed so well, why can't that be used?

From what I'm gathering. Alice measures at angle X, gets value V1 Calls Bob on the phone, okay I measured angle X. Bob measures at angle X, also gets value V1 Bob measures at angle Y, gets value V2. Bob calls Alice back says, okay I measured angle Y. Alice measures angle Y, also gets V2. The correlation here is nobody can do other measurements while the other party is in the process of measuring. Each party can't kno…

I think my mind bend is more over 3 actors. Note that my understanding, also, is that it has been shown that changing a detector changes what is detected at the other detector.

    A is sending entangled stuff to B and C.
    B measures and gets a set of angles that tells them what C would be measuring
    C changes what they are measuring.
The question is, how rapidly does the "spooky" distance change happen? I get that it would not be communication between A and B or C. I similarly get that you could not coordinate between B and C. But, from all of the framings I've seen so far, I don't understand why the change between B and C is not faster than speed of light.

(And just to rapidly get it out there, I fully expect that I'm merely misunderstanding something here.)

Edit: Also, to add, my understanding is that they are not "getting angles" per se, but would be seeing distributions. Which is why you would need more than 1 particle, as it were. So, you would say of the X I have recorded, 30% have been blue, 70% have been green. I suppose the concern is that you have no way of knowing when the "100%" mark is done until after classical communication, such that it is impossible to know what the final distribution you are measuring is? Effectively?

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#112

Post by onlyrealcuzzo »

altruios wrote: post #110

This is my two cents: Maybe entanglement is a much more 'immediately physical' phenomenon than 'spooky action at a distance'. Just guessing as a layman here: maybe entangled particles are just physically connected {along some higher dimension / some unknown process}. Spinning together (effectively switching spaces constantly) such that they are always the same state. So the undetermined measurement stems from being u…

> maybe entangled particles are just physically connected {along some higher dimension / some unknown process}.

I have always thought this might be a possibility - but wouldn't we be able to observe this somehow?

Is it actually possible this could happen and there's no way we could observe it?

Gravity distorts space-time - but it's observable.

For these particles to be connected still - wouldn't that be some disturbance in space-time?

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#113

Post by d_tr »

mrkeen wrote: post #3

The gap I still have in my understanding: One hypothesis is that there is no spooky action. One particle was 'always' going to resolve one way, likewise with the other. Like inspecting 'heads' on one side of a coin 'forces' 'tails' onto the other side. I accept that this coin-hypothesis has been disproved by people who actually know what they're talking about. But to me, this implies that you should build your spooky…

From the perspective of the MWI there is no spooky action.

If you measure one of the particles and look at the result, you then know what term of the quantum state you ended up in, so you know the probability distribution of the other particle's results.

Nature does not need to work according to what our brains consider reasonable, but the MWI getting rid of several very weird notions makes it very appealing, I won't lie...

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#114

Post by superposeur »

gaze wrote: post #51

I’ve been working on quantum computing and quantum communication for 15 years now and what I really want people to know is that entanglement is “beyond classical correlation.” Correlation which is not beyond classical is shaking up a shoebox with a pair of gloves in it, and having two people take the gloves far away from each other to then observe what hand they got. They then understand the hand the other has. There…

> Many quantum information theorists don’t even believe the wave function is “real” but just a mathematical tool for making predictions about measurement outcomes

You are correct that many say this, but this is a constant source of frustration for me (a physicist who does believe the wave function is the only real thing). These physicists never seem to articulate what then is supposed to actually be “real” (under their definition) or what laws govern the “real” things as opposed to the wave function. Implicit seems to be that there is some kind of separate classical realm that obeys non quantum mechanical laws. Is this separate classical realm to be understood as a macroscopic limit of the quantum realm? But if so then the whole picture is circular since wavefunctions are supposed to be mere bookkeeping devices for classical things.

Or to put this more succinctly, if the wave function is a mere bookkeeping device, then bookkeeping for __what__?

(I should mention that yes I know about QBism and all that and my confusion is not for lack of talking to QBists about such things — I just can’t make heads or tails of what they tell me!)

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#115

Post by PaulDavisThe1st »

addaon wrote: post #64
amingilani wrote: post #4

Earlier quoted context omitted.

To expand on this, it uses quantum entanglement for FTL communication over a distance of 4 light years. Still a great story, though.

> To expand on this, it uses quantum entanglement for FTL communication over a distance of 4 light years. Still a great story, though. Although I read the book when it first came out, I have basically zero memory of it, so I don't recall if FTL communication is essential to the story. However, having just watched the first season of the Netflix season, I explicitly noticed that even though it mentions use of FTL comm…

FTL comms are absolutely essential to the story, and it is specifically accomplished using quantum entanglement.

When Evans speaks with the San Ti/Trisolarians, he is talking to them via one of a pair of sophons - quantum entangled protons.

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#116

Post by PaulDavisThe1st »

TheDudeMan wrote: post #59
snapcaster wrote: post #22

Earlier quoted context omitted.

I wanted to like it so badly but the show just didn't hook me. Need to give it another chance sometime

You gotta get through the political stuff in the first episode or so. Just push through. No need to follow it in detail.

s/episode/season/

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#117

Post by PaulDavisThe1st »

azulster wrote: post #65
causi wrote: post #35

Earlier quoted context omitted.

It's dumb on two levels. Firstly, for a planet to evolve sapient life it must be inhabitable for, at minimum, millions of years if not billions, therefore if this orbital instability was going to wipe out the trisolarans it would've done it already. Secondly, the trisolarans are hyper-advanced. They turn individual protons into sapient robots and play with antimatter, therefore they can make a damn air conditioner. M…

broad strokes yes, you are right. however you missed some explanatory details: !!!SPOILERS BELOW!!! the trisolarans specifically evolved to survive their chaotic orbit, by being able to completely "dry out" and wait in stasis for a safer time. this is based on how some worms and bacteria on earth have the ability to survive extreme conditions by similar protective stasis methods. the trisolarans are very intelligent…

> its also implied that the trisolarans did not think themselves very far advanced compared to humans,

not quite. they are aware that they are significantly ahead of humans, but have also observed human scientific and technological progress following an exponential curve, since we do not get our civilization(s) wiped out periodically.

they fear that we will easily catch up with them in 400 years unless they somehow intervene.

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#118

Post by Jensson »

d_tr wrote: post #113
mrkeen wrote: post #3

The gap I still have in my understanding: One hypothesis is that there is no spooky action. One particle was 'always' going to resolve one way, likewise with the other. Like inspecting 'heads' on one side of a coin 'forces' 'tails' onto the other side. I accept that this coin-hypothesis has been disproved by people who actually know what they're talking about. But to me, this implies that you should build your spooky…

From the perspective of the MWI there is no spooky action. If you measure one of the particles and look at the result, you then know what term of the quantum state you ended up in, so you know the probability distribution of the other particle's results. Nature does not need to work according to what our brains consider reasonable, but the MWI getting rid of several very weird notions makes it very appealing, I won't…

> From the perspective of the MWI there is no spooky action.

There is a spooky world split that separates the entire universe instead of just having a spooky thing having to the particle. Some prefers having a small spooky thing over a large spooky thing.

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#119

Post by archgoon »

stephc_int13 wrote: post #33

Most people don't understand enough about the fundamental properties of modern Physics. What we usually call the speed of light is in fact the maximum speed of information propagation. It is not about light, and you should think about quantum entanglement as a hidden variable, there is no magic there.

I mean, it's pretty impressive that Quantum Mechanics forbids FTL communication without referencing the speed of light at all and relies entirely on linearity.

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#120

Post by jayrot »

tombert wrote: post #75

It makes me a little sad, because we're in this frustrating position of knowing how "effectively unlimited" the universe is, but also knowing how impossible it is to realistically explore it, at least not without a fundamental change to our understanding of physics. I think it'd be cool to set up colonies on other planets, or hell, other solar systems, but the inability to communicate seems like a pretty hard blocker…

It’s still wild to me that early exploration (or I suppose colonization) of earth had the same limitation, though. The latency of packet transmission by sailing ship was pretty insane.
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