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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)

#101

Post by trimethylpurine »

Jensson wrote: post #97
bilsbie wrote: post #87

Earlier quoted context omitted.

Thanks. So how is it not analogous to the glove example?

The gloves doesn't change their state when you check on them. Quantum particles do. Example: Lets say you check if the glove is white or black, you see it is white. Then you check if the glove is half white/half black, or half black/half white, you see it is half white/half black. Then you check again if it is white or black, now it is black. That is how quantum gloves would work, but real gloves doesn't work that wa…

>Then you check again

You only get to check once, I think. The rest doesn't matter, supposedly.

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

#102

Post by Jensson »

trimethylpurine wrote: post #101
Jensson wrote: post #97

Earlier quoted context omitted.

The gloves doesn't change their state when you check on them. Quantum particles do. Example: Lets say you check if the glove is white or black, you see it is white. Then you check if the glove is half white/half black, or half black/half white, you see it is half white/half black. Then you check again if it is white or black, now it is black. That is how quantum gloves would work, but real gloves doesn't work that wa…

>Then you check again You only get to check once, I think. The rest doesn't matter, supposedly.

That is false, it changes every time you check along another axis. If you make the same check it doesn't change, but if you change what you check then you can update the particle as my example shows.

Changing a particle like this by making repeated measurements is a standard example in undergrad quantum mechanics.

Edit: There is always a part of the particles state that you can't know, you know Heisenberg's indeterminacy principle, so if you measure position you now makes velocity undetermined, and then if you measure velocity now you make position undetermined, and then if you go back and try to measure position the particle will be in a new random spot.

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

#103

Post by trimethylpurine »

Jensson wrote: post #102
trimethylpurine wrote: post #101

Earlier quoted context omitted.

>Then you check again You only get to check once, I think. The rest doesn't matter, supposedly.

That is false, it changes every time you check along another axis. If you make the same check it doesn't change, but if you change what you check then you can update the particle as my example shows. Changing a particle like this by making repeated measurements is a standard example in undergrad quantum mechanics. Edit: There is always a part of the particles state that you can't know, you know Heisenberg's indetermi…

So if you check that the gloves are black they are black every time you check (axis 1). And then if you check that they have five fingers, they have five fingers every time(axis 2).

So, it sounds exactly like a "gloves in a box" example, right?

I'm not trying to be cheeky, I'm just pointing out that the example really does sound analogous, as stated so far.

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

#104

Post by Jensson »

trimethylpurine wrote: post #103
Jensson wrote: post #102

Earlier quoted context omitted.

That is false, it changes every time you check along another axis. If you make the same check it doesn't change, but if you change what you check then you can update the particle as my example shows. Changing a particle like this by making repeated measurements is a standard example in undergrad quantum mechanics. Edit: There is always a part of the particles state that you can't know, you know Heisenberg's indetermi…

So if you check that the gloves are black they are black every time you check (axis 1). And then if you check that they have five fingers, they have five fingers every time(axis 2). So, it sounds exactly like a "gloves in a box" example, right? I'm not trying to be cheeky, I'm just pointing out that the example really does sound analogous, as stated so far.

It depends on how those states interact with each other. Lets say you can't know a gloves fingers and a gloves color at the same time, so checking number of fingers resets the color and checking color resets number of fingers.

Then if you check number of fingers many times, you get the same result every time. But if you alternate checking fingers and color, you will get random results every time.

Edit: Not that I'm saying this is what original poster meant, just that this is the main difference between quantum particles and our macroscopic objects like gloves.

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

#105

Post by Lerc »

MPSimmons wrote: post #90
joecarrot wrote: post #74

I read a book about particle physics and understood a very small amount of it. My understanding is that you cannot have faster than light anything because nothing can travel faster than light. For instance, the gravitational field of this coffee cup in my hand spans the entire universe. The cup is gravitationally attracting me, the Earth, the Sun, and every other atom in the universe (albeit at a remarkably low level…

Photons, like everything else, travel along the curvature of spacetime (though a physicist has told me that they do have some mass and thus warp spacetime themselves, too), and the speed of light is just how fast spacetime can curve. The faster you go, the more curved it is, and the harder it is to bend it further, but there's a point where you can't bend it any faster than you are because it doesn't go faster.

I always imagined it as everything always moved at the speed of light in spacetime, like 4d motion vectors that were always the same length. Acceleration is changing the angle of the vector to move through more space and less time. Space curvature causes motion on stationary objects (gravity) because of some of the time motion becomes space motion.

I kind of assume this is incorrect because it seems like a simple explanation and explanations of this stuff tend to not be simple

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

#106

Post by spintin »

moate wrote: post #99
spintin wrote: post #84

Earlier quoted context omitted.

lol classic HN down vote without comment...

Lol classic smug comment about HN comment culture acting as if you're owed discourse. FWIW, I'm also pretty sure this type of comment (and therefor my comment?) are against the rules, but I've been rate limited for like 90% of my time here because I don't use burners to get into fights so dafuq do I care. Anyway, hope you have a Good Friday. If it makes you feel better, you're much lower on the crucifixion scale than…

Actually I prefer no comment if you have no arguments:

"While I'm on the topic of concurrency I should mention my far too brief chat with Doug Lea. He commented that multi-threaded Java these days far outperforms C, due to the memory management and a garbage collector. If I recall correctly he said "only 12 times faster than C means you haven't started optimizing"." - Martin Fowler

https://martinfowler.com/bliki/OOPSLA2005.html

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

#107

Post by [deleted] »

taeric wrote: post #67
magicalhippo wrote: post #14

Earlier quoted context omitted.

> If the measurement choices are not aligned, the outcomes are also random Just to be a bit pedantic, as it can otherwise lead to some confusion: the measurement outcomes are always random. If the particles are entangled, then it is the correlations that are not random.

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?

[deleted]

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

#108

Post by kremlin »

leetharris wrote: post #88
joecarrot wrote: post #74

I read a book about particle physics and understood a very small amount of it. My understanding is that you cannot have faster than light anything because nothing can travel faster than light. For instance, the gravitational field of this coffee cup in my hand spans the entire universe. The cup is gravitationally attracting me, the Earth, the Sun, and every other atom in the universe (albeit at a remarkably low level…

The "speed of light" is actually a somewhat poor common name for the limitation. It should be called the "speed of information." If the sun somehow magically disappeared, we would continue to orbit that empty space for about 8 minutes.

or the speed of causality

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

#109

Post by drwiggly »

taeric wrote: post #67
magicalhippo wrote: post #14

Earlier quoted context omitted.

> If the measurement choices are not aligned, the outcomes are also random Just to be a bit pedantic, as it can otherwise lead to some confusion: the measurement outcomes are always random. If the particles are entangled, then it is the correlations that are not random.

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 know the other party is done until traditional communication has happened.

If each party acted independently they would randomly change the state on the other side and each party would get what appears to be random values.

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

#110

Post by altruios »

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 unable to tell which particle specifically you have at the time of measurement.

The idea of a particle's spin being 1/2 feels tied to this idea - (that a 720 rotation happens: if a particle P1 spins 360 in space A, spins 360 in space B before returning to space A, maybe entanglement is P1 and P2 filling space A and B to 'full'?)

In other words - detector A may receive particle B or A depending on the particle's current orientation at measurement.

Weird thoughts. Take with a lot of salt.

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