5 ms·

I'm a dummy. Why does this make them "linked"? If I have two legos, always put them in opposite orientations, then walk away with a random one, being careful t

by nomel 4y ago

I'm a dummy. Why does this make them "linked"? If I have two legos, always put them in opposite orientations, then walk away with a random one, being careful to not change its orientation, are the two legos "linked"? When I look down at the one in my hand, I will know the other ones orientation. How is the different with entangled particles? Is "entangled" just a way to say "still related because it's undisturbed"?

drexlspivey 4y ago
Using your analogy, you don’t put the legos in opposite orientation and walk away with one, it’s more like the two legos keep spinning and you walk away with one and you stop it from spinning and instantaneously the other one stops in the opposite direction.
- wruza 4y ago
  What does “instantaneously” mean if we (afaiu) can’t even have “simultaneously” in general?
  - drdeca 4y ago
    Aiui, it doesn’t at all matter which one is measured “first”, or if the two measurements are spacelike separated such that which one is first depends on frame of reference. Whenever the two measurements are made, they will be correlated in a certain way. You cannot communicate information from one to the other via how you choose to measure them, but you can in some cases coordinate on how your actions are correlated by choosing how to measure based on some info learned on one side. So, if the direction along which A chooses to measure the spin depends on something A learned after A and B went far away from each-other, this can’t change the probabilities of B getting a result of 0 or 1, but it can change the probabilities of things like “A and B both get 1” or “A gets 1 and B gets 0”, etc. , even though not in a way that changes how likely it is for A to get 1, nor how likely for B to get 1. This could conceivably be useful if uh, how useful it is for both parties to do something vs only one party doing it, changes based on the info, I guess?
    - b112 4y ago
      All that pops into my head here, is that in this case, the two particles, when twinned, are actually the same particle... simply at different time references. This behaviour makes zero sense to me otherwise. That makes me think that all particles are actually the same particle, and we're only observing them at different time references. The twinning only objectifies that, so as observers, we are viewing them at time references which allow for known state. Yes, this has a gazillion holes in it. edit: to add to this, there is no reason to infer that because things are separated by distance, they are not the same thing. The universe does not have to play nice, to ensure that humanly derived, evolved logic thinks that things make sense from a classical perspective. If all electrons, for example, are the same electron? Just observed at different time references and locations? Then things such as entanglement make more sense. edit2: What I mean by 'the same particle', is that theoretically all matter in the universe was one ball of whatever prior to the big bang. Everything already is one particle, prior to diffusion and differentiation due to cooling. Thus, every electron in the universe was at one point in time the same, single thing. Therefore, they are the same thing. If time does not exist, it means that this electron here, and over there, can be the same electron, for it can spend <unlimited time> here, and then <unlimited time> there, while at the same moment co-spanning the same time reference as we view it. OK, I'll shut up now, because this is gibberish.
      - garblegarble 4y ago
        >That makes me think that all particles are actually the same particle This sounds similar to Quantum Field Theory[1], which might interest you. I won't try to summarise it here because I don't have a good grasp on it myself, as a layperson (with a below-average understanding of physics, realistically!) 1: https://en.wikipedia.org/wiki/Quantum_field_theory https://en.wikipedia.org/wiki/Quantum_field_theory
        b112 4y ago
        Thanks I shall poke at this.
armchairhacker 4y ago
The way they are linked is that each particle (in this case lego) actually has no orientation until you measure it, it's in a quantum superposition. But the 2 legos are guaranteed to have opposite orientations. One lego has orientation x, the other has !x
- nomel 4y ago
  > until you measure it, it's in a quantum superposition I assume it's been proved that it's in superposition, rather than in a static state? If so, how? Wouldn't knowing require measuring? Or, maybe to make myself more productive, what's a good search term for this? :)
  - assetlabel 4y ago
    Bell's Theorem and the many experiments that followed allegedly prove that they couldn't have taken on any state before measurement, based on probability theory. If they had predetermined states before you measured them, there is a limit to how often an experiment could yield a certain result. But in these experiments, that limit is exceeded. Search for "bell inequality".
  - armchairhacker 4y ago
    There are reliable ways to create superposition particles: when you measure in one direction, the other direction is a superposition (https://physics.stackexchange.com/questions/43974/how-can-we-create-superposition-in-qm https://physics.stackexchange.com/questions/43974/how-can-we...). I have no idea how to create entangled superposition particles: maybe read https://www.eurekalert.org/news-releases/473741 https://www.eurekalert.org/news-releases/473741. You can tell the particles are in a superposition because they behave differently than those in a static state: - Double-split experiment: https://en.wikipedia.org/wiki/Double-slit_experiment https://en.wikipedia.org/wiki/Double-slit_experiment - only particles in a superposition create interference patterns - Bell's paradox: https://www.youtube.com/watch?v=v7jctqKsUMA https://www.youtube.com/watch?v=v7jctqKsUMA, https://www.youtube.com/watch?v=hiyKxhETXd8 https://www.youtube.com/watch?v=hiyKxhETXd8 - entangled particles in a superposition can be measured to make predictions with more confidence than if they were simply static particles with different states I guess a good search term would be "Polarized light and quantum mechanics" because IMO polarized light is a good example which you can even simulate yourself if you have a polarizing filter (https://www.youtube.com/watch?v=zcqZHYo7ONs&t=736s https://www.youtube.com/watch?v=zcqZHYo7ONs&t=736s, https://www.youtube.com/watch?v=ZudziPffS9E https://www.youtube.com/watch?v=ZudziPffS9E, https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Quantum_Tutorials_(Rioux)/Quantum_Fundamentals/08%3A_Quantum_Principles_Illuminated_with_Polarized_Light https://chem.libretexts.org/Bookshelves/Physical_and_Theoret...)
shagie 4y ago
Its... weirder than that. The issue is that the measurement of the particle changes it - and changes the entangled particle. PBS Space Time - Quantum Entanglement and the Great Bohr-Einstein Debate https://youtu.be/tafGL02EUOA https://youtu.be/tafGL02EUOA (and then watch the referenced Veritasium video)
wyager 4y ago
You're describing a Hidden Variable Theory, which does not work https://en.wikipedia.org/wiki/Hidden-variable_theory https://en.wikipedia.org/wiki/Hidden-variable_theory
- mtlmtlmtlmtl 4y ago
  Local hidden variable theories are ruled out by Bell's Theorem. Not hidden variable theories in general. I realise GP was describing a local HVT, but it's still an important distinction.
- tadfisher 4y ago
  Sure it can. Bell's theorem implies you can have locality or hidden variables, but not both. de Broglie-Bohm is an example of a non-local hidden-variable theory.
Dylan16807 4y ago
So that's called "hidden variable theory". We've done tests that show it's not true. Basically, there are certain measurements you can do on entangled particles where you can prove each measurement is affecting the other measurement.
- rightbyte 4y ago
  Sounds like the physicists maybe mixed up the concepts of correlation and causality.
  - Dylan16807 4y ago
    Mixed up in what way? Note that if you have two observers a light-second apart, and they only choose what measurement to do 0.01 seconds before performing it, at least one of those choices affects both results.
- Winsaucerer 4y ago
  These tests you are referring to, are they a recent discovery? There is a long repeated misconception that violations of Bell's theorem has shown hidden variable theories to be false. If that's what you're referring to, then no we haven't. If, on the other hand, there's been some developments in the last 5 or 10 years, then it's very likely I've missed those. If you are referring to violations of Bell's theorem, then what they show is that hidden variables are incompatible with locality. In other words, non-local hidden variable theories are compatible with these violations and have not been shown to be false.
  - Dylan16807 4y ago
    The whole point is to show that something non-local is happening (or an equivalent), so of course I'm talking about local hidden variables. I don't understand your objection. I'm being a little loose about casualty but that's because I don't want to write extra paragraphs about what "simultaneous" means.
    - 4y ago

by nomel 4y ago

drexlspivey 4y ago

Using your analogy, you don’t put the legos in opposite orientation and walk away with one, it’s more like the two legos keep spinning and you walk away with one and you stop it from spinning and instantaneously the other one stops in the opposite direction.

wruza 4y ago
What does “instantaneously” mean if we (afaiu) can’t even have “simultaneously” in general?
- drdeca 4y ago
  Aiui, it doesn’t at all matter which one is measured “first”, or if the two measurements are spacelike separated such that which one is first depends on frame of reference. Whenever the two measurements are made, they will be correlated in a certain way. You cannot communicate information from one to the other via how you choose to measure them, but you can in some cases coordinate on how your actions are correlated by choosing how to measure based on some info learned on one side. So, if the direction along which A chooses to measure the spin depends on something A learned after A and B went far away from each-other, this can’t change the probabilities of B getting a result of 0 or 1, but it can change the probabilities of things like “A and B both get 1” or “A gets 1 and B gets 0”, etc. , even though not in a way that changes how likely it is for A to get 1, nor how likely for B to get 1. This could conceivably be useful if uh, how useful it is for both parties to do something vs only one party doing it, changes based on the info, I guess?
  - b112 4y ago
    All that pops into my head here, is that in this case, the two particles, when twinned, are actually the same particle... simply at different time references. This behaviour makes zero sense to me otherwise. That makes me think that all particles are actually the same particle, and we're only observing them at different time references. The twinning only objectifies that, so as observers, we are viewing them at time references which allow for known state. Yes, this has a gazillion holes in it. edit: to add to this, there is no reason to infer that because things are separated by distance, they are not the same thing. The universe does not have to play nice, to ensure that humanly derived, evolved logic thinks that things make sense from a classical perspective. If all electrons, for example, are the same electron? Just observed at different time references and locations? Then things such as entanglement make more sense. edit2: What I mean by 'the same particle', is that theoretically all matter in the universe was one ball of whatever prior to the big bang. Everything already is one particle, prior to diffusion and differentiation due to cooling. Thus, every electron in the universe was at one point in time the same, single thing. Therefore, they are the same thing. If time does not exist, it means that this electron here, and over there, can be the same electron, for it can spend <unlimited time> here, and then <unlimited time> there, while at the same moment co-spanning the same time reference as we view it. OK, I'll shut up now, because this is gibberish.
    - garblegarble 4y ago
      >That makes me think that all particles are actually the same particle This sounds similar to Quantum Field Theory[1], which might interest you. I won't try to summarise it here because I don't have a good grasp on it myself, as a layperson (with a below-average understanding of physics, realistically!) 1: https://en.wikipedia.org/wiki/Quantum_field_theory https://en.wikipedia.org/wiki/Quantum_field_theory
      - b112 4y ago
        Thanks I shall poke at this.

armchairhacker 4y ago

The way they are linked is that each particle (in this case lego) actually has no orientation until you measure it, it's in a quantum superposition. But the 2 legos are guaranteed to have opposite orientations. One lego has orientation x, the other has !x

nomel 4y ago
> until you measure it, it's in a quantum superposition I assume it's been proved that it's in superposition, rather than in a static state? If so, how? Wouldn't knowing require measuring? Or, maybe to make myself more productive, what's a good search term for this? :)
- assetlabel 4y ago
  Bell's Theorem and the many experiments that followed allegedly prove that they couldn't have taken on any state before measurement, based on probability theory. If they had predetermined states before you measured them, there is a limit to how often an experiment could yield a certain result. But in these experiments, that limit is exceeded. Search for "bell inequality".
- armchairhacker 4y ago
  There are reliable ways to create superposition particles: when you measure in one direction, the other direction is a superposition (https://physics.stackexchange.com/questions/43974/how-can-we-create-superposition-in-qm https://physics.stackexchange.com/questions/43974/how-can-we...). I have no idea how to create entangled superposition particles: maybe read https://www.eurekalert.org/news-releases/473741 https://www.eurekalert.org/news-releases/473741. You can tell the particles are in a superposition because they behave differently than those in a static state: - Double-split experiment: https://en.wikipedia.org/wiki/Double-slit_experiment https://en.wikipedia.org/wiki/Double-slit_experiment - only particles in a superposition create interference patterns - Bell's paradox: https://www.youtube.com/watch?v=v7jctqKsUMA https://www.youtube.com/watch?v=v7jctqKsUMA, https://www.youtube.com/watch?v=hiyKxhETXd8 https://www.youtube.com/watch?v=hiyKxhETXd8 - entangled particles in a superposition can be measured to make predictions with more confidence than if they were simply static particles with different states I guess a good search term would be "Polarized light and quantum mechanics" because IMO polarized light is a good example which you can even simulate yourself if you have a polarizing filter (https://www.youtube.com/watch?v=zcqZHYo7ONs&t=736s https://www.youtube.com/watch?v=zcqZHYo7ONs&t=736s, https://www.youtube.com/watch?v=ZudziPffS9E https://www.youtube.com/watch?v=ZudziPffS9E, https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Quantum_Tutorials_(Rioux)/Quantum_Fundamentals/08%3A_Quantum_Principles_Illuminated_with_Polarized_Light https://chem.libretexts.org/Bookshelves/Physical_and_Theoret...)

shagie 4y ago

Its... weirder than that. The issue is that the measurement of the particle changes it - and changes the entangled particle. PBS Space Time - Quantum Entanglement and the Great Bohr-Einstein Debate https://youtu.be/tafGL02EUOA https://youtu.be/tafGL02EUOA (and then watch the referenced Veritasium video)

wyager 4y ago

You're describing a Hidden Variable Theory, which does not work https://en.wikipedia.org/wiki/Hidden-variable_theory https://en.wikipedia.org/wiki/Hidden-variable_theory

mtlmtlmtlmtl 4y ago
Local hidden variable theories are ruled out by Bell's Theorem. Not hidden variable theories in general. I realise GP was describing a local HVT, but it's still an important distinction.
tadfisher 4y ago
Sure it can. Bell's theorem implies you can have locality or hidden variables, but not both. de Broglie-Bohm is an example of a non-local hidden-variable theory.

Dylan16807 4y ago

So that's called "hidden variable theory". We've done tests that show it's not true. Basically, there are certain measurements you can do on entangled particles where you can prove each measurement is affecting the other measurement.

rightbyte 4y ago
Sounds like the physicists maybe mixed up the concepts of correlation and causality.
- Dylan16807 4y ago
  Mixed up in what way? Note that if you have two observers a light-second apart, and they only choose what measurement to do 0.01 seconds before performing it, at least one of those choices affects both results.
Winsaucerer 4y ago
These tests you are referring to, are they a recent discovery? There is a long repeated misconception that violations of Bell's theorem has shown hidden variable theories to be false. If that's what you're referring to, then no we haven't. If, on the other hand, there's been some developments in the last 5 or 10 years, then it's very likely I've missed those. If you are referring to violations of Bell's theorem, then what they show is that hidden variables are incompatible with locality. In other words, non-local hidden variable theories are compatible with these violations and have not been shown to be false.
- Dylan16807 4y ago
  The whole point is to show that something non-local is happening (or an equivalent), so of course I'm talking about local hidden variables. I don't understand your objection. I'm being a little loose about casualty but that's because I don't want to write extra paragraphs about what "simultaneous" means.
  - 4y ago