7 ms·

Entanglement isn't like how it's described in the post at all. Entangled particles are correlated across spacetime in a way that goes beyond "instantly knowing

by emrah 5y ago

Entanglement isn't like how it's described in the post at all. Entangled particles are correlated across spacetime in a way that goes beyond "instantly knowing there is red in one envelope when blue is in the other". First of all, we don't know which color is in which envelope at the start. And revealing of one instantly determines the other physically regardless of whether it came up red or blue. So entanglement is "spooky action at a distance". This property doesn't constitute FTL communication though since we can't encode any information this way, we don't know what the particles will reveal when measured. We just know that measuring one will affect the other particle no matter how far apart they are physically. So I imagine Einstein meant both.

headmelted 5y ago
I was trying to think of a way to explain this to a family member a while back who had a background in mechanical engineering. The best example I could think of to analogise it were meshed gears. There is no messaging happening between them. When one rotates, the other rotates in the opposite direction at the same exact time because they are interlinked. They are two parts of one connected set. That entangled particles are interlinked in this way shouldn’t be surprising. Having what to us seem to be arbitrary distances between the particles could simply mean that they’re interlinked outside of the three spatial dimensions we’re used to perceiving the universe in - but this last part is just my own understanding and I’m quite happy for someone who knows better to tell me if (and why) it’s wrong.
- TeMPOraL 5y ago
  > There is no messaging happening between [meshed gears]. Isn't there? Atoms rub against atoms, electric fields interact and transfer forces. The gears communicate by touching, but it happens so fast that it looks instantaneous. This can be experimentally verified by weakening one of the teeth of one gear, and driving some load with that gear set - eventually, the weakened tooth will break off.
  - rleigh 5y ago
    There is messaging through physical contact. It occurs at the speed of sound as opposed to the speed of light.
    - redis_mlc 5y ago
      No, physical ("intermolecular") forces are electromagnetic, and the force between atoms is transmitted at the speed of light. Vibration in gears travels at the speed of sound for the material that the gears are made of, but that is not what separates the gears physically from merging at an atomic level.
    - deleted 5y ago
      [deleted]
  - headmelted 5y ago
    If there’s a delay, it’s not perceptible to an onlooker, which is probably good enough for an analogy in this case I hope? It would need to be, given that the gears aren’t going to reverse time and break apart into light beams just because I looked at them. Quantum physics doesn’t fit very well into simple examples.
russdill 5y ago
The envelope description doesn't allow the core of the issue to be expressed. Just allowing for a single measurement of a single property is completely uninteresting. Being able to measure spin at arbitrary angles is the best description, but I don't know any good analogies to it, especially ones involving envelopes.
- k__ 5y ago
  Yes. The envelope example always seem obvious. But when particle physicists talk about the problem, it sounds like it isn't that obvious.
  - eigenket 5y ago
    I don't think many physicists really think of entanglement as a problem now. Its kinda weird, but its also completely consistent, doesn't lead to any wild paradoxes and turns out to be very useful in a variety of scenarios. I think there are people who are concerned with the foundations of quantum mechanics more generally, and they might be concerned with entanglement as an emergent feature of the weirdness in the foundations they don't like, but most of the work I see these days is on interesting ways to use entanglement.
    - tarsinge 5y ago
      That’s a good point and a lot of incomprehensions come from that, in classical physics you can develop an intuitive understanding of the how with the foundation, but in QM it’s distinct. Physicist usually only answer on the how because that’s where the work is (“entanglement works like this, here is the model”) but there is interest in the foundation too, even if it’s a bit philosophical.
deleted 5y ago
[deleted]
zelphirkalt 5y ago
You state this as a fact, but there seems to be an interpretation of entanglement in what you wrote, so I will ask a question: Sticking to the metapher, how do you know, that looking at the content of one envelope will _affect_ the content of the other envelope, in contrast to you _discovering_ the other envelope's content to be the other color? Asked differently: Why do you necessitate that viewing one envelope's content _affects_ the other, rather than merely allowing to conclude the other, because some law of the universe makes it happen to be always the other color? To me this seems really an interpretation, rather than a fact, that one can simply put there without dispute.
- simcop2387 5y ago
  Part of this is because of tests like the ones involved with Bells theorem. Minute physics does a better job explaining it then I can. https://m.youtube.com/watch?v=zcqZHYo7ONs&vl=en https://m.youtube.com/watch?v=zcqZHYo7ONs&vl=en
- ahelwer 5y ago
  This is something you can experimentally test. First you should know that "red ball or blue ball" is a simplification. Staying with the metaphor, if you open one envelope differently you might get a purple ball and so know the other envelope contains a green ball. What we're actually dealing with are vectors on the complex unit sphere instead of ball colors, and opening the envelope is choosing two perpendicular axes along which to measure the state, causing probabilistic collapse to one or the other axis. Since you can choose which axes you measure, there are all sorts of tricky experiments you can do (called Bell tests) to test the theory that you're just discovering a pre-existing value vs. causing collapse to those values. The pre-existing value idea is called a local hidden variable, the existence of which has been conclusively experimentally disproven. I wrote a post on this you might find useful, explaining a Bell test called the CHSH game that computer scientists will find intuitive. All you need is your rememberance of the unit circle from high school path! https://ahelwer.ca/post/2018-12-07-chsh/ https://ahelwer.ca/post/2018-12-07-chsh/
  - zelphirkalt 5y ago
IncRnd 5y ago
Well, Einstein prefaced that exact portion by saying, "To see what I mean, forget all about quantum mechanics for a moment." You misunderstood what he wrote. He did not describe entanglement when discussing the red and blue pair of socks. He was creating an analogy to build his argument that he later transferred to "spooky action at a distance".
DebtDeflation 5y ago
>Entanglement isn't like how it's described in the post at all. Entangled particles are correlated across spacetime in a way that goes beyond "instantly knowing there is red in one envelope when blue is in the other". When I watched this on YouTube yesterday, I knew that as soon as she used the sock example that someone would get salty about it without listening to the rest of what she says. She addresses this right towards the end: "Yes, that explains the case for the socks. But in quantum mechanics, that explanation does not work. If you think that really it was decided already which spin went into which direction when they were emitted, that will not create sufficiently strong correlations. It’s just incompatible with observations." >So I imagine Einstein meant both I think her view is that when Einstein said "spooky action at a distance" he was referring SPECIFICALLY to the instantaneous effect of measurement on the wave function. Entanglement, then, is just an example of this where we can increase the distance in the lab to experimentally confirm the implication.
- deleted 5y ago
  [deleted]

by emrah 5y ago

headmelted 5y ago

I was trying to think of a way to explain this to a family member a while back who had a background in mechanical engineering. The best example I could think of to analogise it were meshed gears. There is no messaging happening between them. When one rotates, the other rotates in the opposite direction at the same exact time because they are interlinked. They are two parts of one connected set. That entangled particles are interlinked in this way shouldn’t be surprising. Having what to us seem to be arbitrary distances between the particles could simply mean that they’re interlinked outside of the three spatial dimensions we’re used to perceiving the universe in - but this last part is just my own understanding and I’m quite happy for someone who knows better to tell me if (and why) it’s wrong.

TeMPOraL 5y ago
> There is no messaging happening between [meshed gears]. Isn't there? Atoms rub against atoms, electric fields interact and transfer forces. The gears communicate by touching, but it happens so fast that it looks instantaneous. This can be experimentally verified by weakening one of the teeth of one gear, and driving some load with that gear set - eventually, the weakened tooth will break off.
- rleigh 5y ago
  There is messaging through physical contact. It occurs at the speed of sound as opposed to the speed of light.
  - redis_mlc 5y ago
    No, physical ("intermolecular") forces are electromagnetic, and the force between atoms is transmitted at the speed of light. Vibration in gears travels at the speed of sound for the material that the gears are made of, but that is not what separates the gears physically from merging at an atomic level.
  - deleted 5y ago
    [deleted]
- headmelted 5y ago
  If there’s a delay, it’s not perceptible to an onlooker, which is probably good enough for an analogy in this case I hope? It would need to be, given that the gears aren’t going to reverse time and break apart into light beams just because I looked at them. Quantum physics doesn’t fit very well into simple examples.

russdill 5y ago

The envelope description doesn't allow the core of the issue to be expressed. Just allowing for a single measurement of a single property is completely uninteresting. Being able to measure spin at arbitrary angles is the best description, but I don't know any good analogies to it, especially ones involving envelopes.

k__ 5y ago
Yes. The envelope example always seem obvious. But when particle physicists talk about the problem, it sounds like it isn't that obvious.
- eigenket 5y ago
  I don't think many physicists really think of entanglement as a problem now. Its kinda weird, but its also completely consistent, doesn't lead to any wild paradoxes and turns out to be very useful in a variety of scenarios. I think there are people who are concerned with the foundations of quantum mechanics more generally, and they might be concerned with entanglement as an emergent feature of the weirdness in the foundations they don't like, but most of the work I see these days is on interesting ways to use entanglement.
  - tarsinge 5y ago
    That’s a good point and a lot of incomprehensions come from that, in classical physics you can develop an intuitive understanding of the how with the foundation, but in QM it’s distinct. Physicist usually only answer on the how because that’s where the work is (“entanglement works like this, here is the model”) but there is interest in the foundation too, even if it’s a bit philosophical.

deleted 5y ago

[deleted]

zelphirkalt 5y ago

You state this as a fact, but there seems to be an interpretation of entanglement in what you wrote, so I will ask a question: Sticking to the metapher, how do you know, that looking at the content of one envelope will _affect_ the content of the other envelope, in contrast to you _discovering_ the other envelope's content to be the other color? Asked differently: Why do you necessitate that viewing one envelope's content _affects_ the other, rather than merely allowing to conclude the other, because some law of the universe makes it happen to be always the other color? To me this seems really an interpretation, rather than a fact, that one can simply put there without dispute.

simcop2387 5y ago
Part of this is because of tests like the ones involved with Bells theorem. Minute physics does a better job explaining it then I can. https://m.youtube.com/watch?v=zcqZHYo7ONs&vl=en https://m.youtube.com/watch?v=zcqZHYo7ONs&vl=en
ahelwer 5y ago
This is something you can experimentally test. First you should know that "red ball or blue ball" is a simplification. Staying with the metaphor, if you open one envelope differently you might get a purple ball and so know the other envelope contains a green ball. What we're actually dealing with are vectors on the complex unit sphere instead of ball colors, and opening the envelope is choosing two perpendicular axes along which to measure the state, causing probabilistic collapse to one or the other axis. Since you can choose which axes you measure, there are all sorts of tricky experiments you can do (called Bell tests) to test the theory that you're just discovering a pre-existing value vs. causing collapse to those values. The pre-existing value idea is called a local hidden variable, the existence of which has been conclusively experimentally disproven. I wrote a post on this you might find useful, explaining a Bell test called the CHSH game that computer scientists will find intuitive. All you need is your rememberance of the unit circle from high school path! https://ahelwer.ca/post/2018-12-07-chsh/ https://ahelwer.ca/post/2018-12-07-chsh/
- zelphirkalt 5y ago

IncRnd 5y ago

Well, Einstein prefaced that exact portion by saying, "To see what I mean, forget all about quantum mechanics for a moment." You misunderstood what he wrote. He did not describe entanglement when discussing the red and blue pair of socks. He was creating an analogy to build his argument that he later transferred to "spooky action at a distance".

DebtDeflation 5y ago

>Entanglement isn't like how it's described in the post at all. Entangled particles are correlated across spacetime in a way that goes beyond "instantly knowing there is red in one envelope when blue is in the other". When I watched this on YouTube yesterday, I knew that as soon as she used the sock example that someone would get salty about it without listening to the rest of what she says. She addresses this right towards the end: "Yes, that explains the case for the socks. But in quantum mechanics, that explanation does not work. If you think that really it was decided already which spin went into which direction when they were emitted, that will not create sufficiently strong correlations. It’s just incompatible with observations." >So I imagine Einstein meant both I think her view is that when Einstein said "spooky action at a distance" he was referring SPECIFICALLY to the instantaneous effect of measurement on the wave function. Entanglement, then, is just an example of this where we can increase the distance in the lab to experimentally confirm the implication.

deleted 5y ago
[deleted]