4 ms·

Entanglement is like splitting a coin in half, so you have a tails and a head half. Then you put one in your left pocket and give the other to a friend. Then,

Entanglement is like splitting a coin in half, so you have a tails and a head half. Then you put one in your left pocket and give the other to a friend. Then, just by looking in your left pocket, you can learn that your friend has the heads half—instantly! In other words, it’s not as spooky as it is made out to be.

sincerecook 2y ago
In this case the coin is neither heads nor tails until you check it and then it becomes one or the other and it's counterpart becomes the opposite, no matter how far apart they are. So yeah it's kind of spooky.
- HappMacDonald 2y ago
  My understanding is that entanglement has nothing to do with the particles and everything to do with what is known about the particles in advance by dint of the experimental setup. For example, that two electrons are created in a closed system with a net spin of zero, so as long as you do not allow their waveforms to collapse (EG, so long as the system remains closed) then no matter where they go they must maintain that net spin of zero when perceived in relation to one another. But if this is the case then the "entanglement" precedes the creation of the particles: it is nothing more than an accounting that they are required to obey in concert by the symmetries of physics.
akomtu 2y ago
It's more like splitting the timeline in half: in one branch it's heads, in the other it's tails, and you don't know which timeline you're in until you look at the coin. The Bell's inequality says the coin has no state until it's been observed.
tzs 2y ago
That's not correct. With entanglement you get correlations that you cannot get if the states of a pair of particles are determined at creation time. There's a neat game called the CHSH game that illustrates this. Here's a description [1]. Here's a puzzle equivalent to CHSH but that might be easier for programmers to visualize [1]. [1] https://news.ycombinator.com/item?id=41393075 https://news.ycombinator.com/item?id=41393075 [2] https://news.ycombinator.com/item?id=35905284 https://news.ycombinator.com/item?id=35905284
- bawolff 2y ago
  I mean the person you were responding to said "like". I think splitting a coin is a reasonable but not perfect analogy.
  - tzs 2y ago
    The splitting a coin analogy doesn't capture anything about entanglement though. It is just capturing a property of all distinguishable persistent objects: if you have two distinguishable persistent objects and you know one is at location A and one is at location B, then if you find out which one is at A you know what the one at B must be. To be a reasonable analogy it has to capture something this is different between entangled and not entangled particles. That's the thing that is sometimes described as "spooky" and completely missing from the split coin analogy.
    - bawolff 2y ago
      Its capturing that the two particles are correlated instead of transfering information. I feel like that is the core part to understand.
      - tzs 2y ago
        But correlations like that happen all the time. You put the tape that was supposed to "Back Door Sluts 9" into the VCR and see that it is "Lord of the Rings" then you immediately know that when you gave your kids "Lord of the Rings" to take to a friends house you got the tapes swapped and the kids are now walking around with the hottest porno ever made. You know this because the two tapes are correlated because you rented them together and have no other rental tapes. No information had to be transferred for you to know the kids have BDS9. Or your daughter Lisa calls from school and tells you there is meat in her lunch. You immediately know that you must have mixed up the bag lunches that morning and Bart had the vegan meal. You make the lunches together, one vegan and one not, so they are correlated without information transfer. What makes entangled particles different from other pairs of correlated things is that they correlate in ways the seem impossible without communication. It's like if someone answered the question of why frogs sometimes rain from the sky by saying that because frogs cannot fly and are heavier than air, just like hail or rain or snowflakes, they feel a downward force from gravity which pulls them to the ground. It's right...but no one has trouble understanding the gravitational aspect of frogs falling from the sky. The thing people want to understand is how a bunch of freaking frogs got into the sky in the first place.
ziofill 2y ago
Classical analogies only go so far. What's spooky about entanglement is that it works even if you change the measurement basis (as long as the two parts are using the same basis), which you cannot do with a coin.
mr_toad 2y ago
It’s more like looking in your pocket and finding that sometimes it’s actually become a head due to beta decay, and spookily your friend now instantly has tails.
ozzydave 2y ago
Gotta love the confidence to casually think every physicist for the past 100 years is an idiot.
magicalhippo 2y ago
> In other words, it’s not as spooky as it is made out to be. That's not really the spooky part of entanglement. The rabbit hole goes much deeper, like here[1] or here[2]. [1]: https://arxiv.org/abs/1203.4834 https://arxiv.org/abs/1203.4834 [2]: https://arxiv.org/abs/1209.4191 https://arxiv.org/abs/1209.4191

sincerecook 2y ago

In this case the coin is neither heads nor tails until you check it and then it becomes one or the other and it's counterpart becomes the opposite, no matter how far apart they are. So yeah it's kind of spooky.

HappMacDonald 2y ago
My understanding is that entanglement has nothing to do with the particles and everything to do with what is known about the particles in advance by dint of the experimental setup. For example, that two electrons are created in a closed system with a net spin of zero, so as long as you do not allow their waveforms to collapse (EG, so long as the system remains closed) then no matter where they go they must maintain that net spin of zero when perceived in relation to one another. But if this is the case then the "entanglement" precedes the creation of the particles: it is nothing more than an accounting that they are required to obey in concert by the symmetries of physics.

akomtu 2y ago

It's more like splitting the timeline in half: in one branch it's heads, in the other it's tails, and you don't know which timeline you're in until you look at the coin. The Bell's inequality says the coin has no state until it's been observed.

tzs 2y ago

That's not correct. With entanglement you get correlations that you cannot get if the states of a pair of particles are determined at creation time. There's a neat game called the CHSH game that illustrates this. Here's a description [1]. Here's a puzzle equivalent to CHSH but that might be easier for programmers to visualize [1]. [1] https://news.ycombinator.com/item?id=41393075 https://news.ycombinator.com/item?id=41393075 [2] https://news.ycombinator.com/item?id=35905284 https://news.ycombinator.com/item?id=35905284

bawolff 2y ago
I mean the person you were responding to said "like". I think splitting a coin is a reasonable but not perfect analogy.
- tzs 2y ago
  The splitting a coin analogy doesn't capture anything about entanglement though. It is just capturing a property of all distinguishable persistent objects: if you have two distinguishable persistent objects and you know one is at location A and one is at location B, then if you find out which one is at A you know what the one at B must be. To be a reasonable analogy it has to capture something this is different between entangled and not entangled particles. That's the thing that is sometimes described as "spooky" and completely missing from the split coin analogy.
  - bawolff 2y ago
    Its capturing that the two particles are correlated instead of transfering information. I feel like that is the core part to understand.
    - tzs 2y ago
      But correlations like that happen all the time. You put the tape that was supposed to "Back Door Sluts 9" into the VCR and see that it is "Lord of the Rings" then you immediately know that when you gave your kids "Lord of the Rings" to take to a friends house you got the tapes swapped and the kids are now walking around with the hottest porno ever made. You know this because the two tapes are correlated because you rented them together and have no other rental tapes. No information had to be transferred for you to know the kids have BDS9. Or your daughter Lisa calls from school and tells you there is meat in her lunch. You immediately know that you must have mixed up the bag lunches that morning and Bart had the vegan meal. You make the lunches together, one vegan and one not, so they are correlated without information transfer. What makes entangled particles different from other pairs of correlated things is that they correlate in ways the seem impossible without communication. It's like if someone answered the question of why frogs sometimes rain from the sky by saying that because frogs cannot fly and are heavier than air, just like hail or rain or snowflakes, they feel a downward force from gravity which pulls them to the ground. It's right...but no one has trouble understanding the gravitational aspect of frogs falling from the sky. The thing people want to understand is how a bunch of freaking frogs got into the sky in the first place.

ziofill 2y ago

Classical analogies only go so far. What's spooky about entanglement is that it works even if you change the measurement basis (as long as the two parts are using the same basis), which you cannot do with a coin.

mr_toad 2y ago

It’s more like looking in your pocket and finding that sometimes it’s actually become a head due to beta decay, and spookily your friend now instantly has tails.

ozzydave 2y ago

Gotta love the confidence to casually think every physicist for the past 100 years is an idiot.

magicalhippo 2y ago

> In other words, it’s not as spooky as it is made out to be. That's not really the spooky part of entanglement. The rabbit hole goes much deeper, like here[1] or here[2]. [1]: https://arxiv.org/abs/1203.4834 https://arxiv.org/abs/1203.4834 [2]: https://arxiv.org/abs/1209.4191 https://arxiv.org/abs/1209.4191