4 ms·

I dislike all writings on quantum entanglement as they seem more interested in clickbaiting than actually communicating actual knowledge. Two contradictory tal

by hsn915 4y ago

I dislike all writings on quantum entanglement as they seem more interested in clickbaiting than actually communicating actual knowledge. Two contradictory talking points seem to be pervasive: - Altering one atom affects the other instantaniously - There's no FTL communication going on, it's just a correlation, even though we have told you before that quantum correlations are not like classic correlations, and even though we have told you that the atoms don't have any settled state until you measure them Basically, never take seriously anything written about quantum physics in pop-science magazines.

saargrin 4y ago
so is this legit or not?
- deleted 4y ago
  [deleted]
TrapLord_Rhodo 4y ago
Paul Revere entangled: Say i entangle two atoms and send one of the atoms to mars, which is 8 lightseconds away. I tell you before you leave that if the poles of the atom where to flip, the british are coming. If i were to flip the atom in one second, you were to measure it the next second you were still able to exchange information 4X faster than the speed of light. Or am i missing something and no one actually understands any of this?
- netcraft 4y ago
  You would have to know when to measure. If you on mars measure too soon, youre the one forcing the other atom to flip. You also wouldnt know that you had done that. (I think, IANAQP)
  - oneoff786 4y ago
    That could be agreed upon ahead of time.
  - hsn915 4y ago
    That's not how it works. At long enough distances, "before" and "after" are only relatively defined. That's the whole point of relativity. Two events A and B can occur "A first, then B" in one reference frame, but "B first, then A" in another reference frame.
- baq 4y ago
  > send one of the atoms to mars The answer is in the question.
- isaacg 4y ago
  This is not how entanglement works, and while people do understand how entanglement works, it's a little subtle. When you measure your atom on earth, you will get results with certain probabilities. When I measure my atom on the moon, I will get results with certain probabilities. My probabilities don't depend on how you performed your measurement - I can't tell what measurement you performed from just the results of my measurement. However, our results will be correlated in unusual ways depending on our measurements. Maybe we both get a spin up result, or both get a spin down result. These correlations go beyond the amount of correlation it's possible for classical objects to have, which is the essence of the Bell experiment, and specifically the CHSH inequality. So entanglement can't be used to tell someone that the British are coming faster than normal classical communication. But it could be use to coordinate our responses (maybe both attack or both retreat, or one of each, with certain probabilities) in ways that can't be reproduced classically without using communication. Hope that helps.
  - anon1038471 4y ago
    If I understand it correctly, two entangled qbits can can have their spin measured in the same order of planes (XY, YZ, XZ) to get the same result? So you can send a binary bit {0:no british, 1:british} or a qbit{XY:british probability, some other strategy dependent on XY spin and order of spin planes?}
    - isaacg 4y ago
      No, it is not possible to communicate any information by measuring one side of the quantum state. This is the no communication theorem: https://en.m.wikipedia.org/wiki/No-communication_theorem https://en.m.wikipedia.org/wiki/No-communication_theorem It's only possible to achieve correlations that are stronger than are classically possible without communication. Communication itself still cannot be achieved, by any sequence of measurements.
      - TrapLord_Rhodo 4y ago
        Taken from your wiki link with a twist; "spooky correlation at a distance" does seem to be some amount of information. The paul revere joke was entirely out of scope, but the universe does seem to have some way to pull the strings behind the curtain here.
- deleted 4y ago
  [deleted]
- hsn915 4y ago
  I don't care that you can't use it to communicate FTL. I care that the atoms are doing it or not.
kgwgk 4y ago
> Two contradictory talking points seem to be pervasive: They are not really contradictory. > - Altering one atom affects the other instantaniously It kind-of does, if by "affecting the other" you mean changing the physical state of the pair from "the A/B system is in state S0" to "A is in state SA and B is in state SB". > - There's no FTL communication going on, There isn't unless you want to define as "communication" the change in the physical state described above. > Basically, never take seriously anything written about quantum physics in pop-science magazines. That's unfortunately a wise advice.

by hsn915 4y ago

saargrin 4y ago

so is this legit or not?

deleted 4y ago
[deleted]

TrapLord_Rhodo 4y ago

Paul Revere entangled: Say i entangle two atoms and send one of the atoms to mars, which is 8 lightseconds away. I tell you before you leave that if the poles of the atom where to flip, the british are coming. If i were to flip the atom in one second, you were to measure it the next second you were still able to exchange information 4X faster than the speed of light. Or am i missing something and no one actually understands any of this?

netcraft 4y ago
You would have to know when to measure. If you on mars measure too soon, youre the one forcing the other atom to flip. You also wouldnt know that you had done that. (I think, IANAQP)
- oneoff786 4y ago
  That could be agreed upon ahead of time.
- hsn915 4y ago
  That's not how it works. At long enough distances, "before" and "after" are only relatively defined. That's the whole point of relativity. Two events A and B can occur "A first, then B" in one reference frame, but "B first, then A" in another reference frame.
baq 4y ago
> send one of the atoms to mars The answer is in the question.
isaacg 4y ago
This is not how entanglement works, and while people do understand how entanglement works, it's a little subtle. When you measure your atom on earth, you will get results with certain probabilities. When I measure my atom on the moon, I will get results with certain probabilities. My probabilities don't depend on how you performed your measurement - I can't tell what measurement you performed from just the results of my measurement. However, our results will be correlated in unusual ways depending on our measurements. Maybe we both get a spin up result, or both get a spin down result. These correlations go beyond the amount of correlation it's possible for classical objects to have, which is the essence of the Bell experiment, and specifically the CHSH inequality. So entanglement can't be used to tell someone that the British are coming faster than normal classical communication. But it could be use to coordinate our responses (maybe both attack or both retreat, or one of each, with certain probabilities) in ways that can't be reproduced classically without using communication. Hope that helps.
- anon1038471 4y ago
  If I understand it correctly, two entangled qbits can can have their spin measured in the same order of planes (XY, YZ, XZ) to get the same result? So you can send a binary bit {0:no british, 1:british} or a qbit{XY:british probability, some other strategy dependent on XY spin and order of spin planes?}
  - isaacg 4y ago
    No, it is not possible to communicate any information by measuring one side of the quantum state. This is the no communication theorem: https://en.m.wikipedia.org/wiki/No-communication_theorem https://en.m.wikipedia.org/wiki/No-communication_theorem It's only possible to achieve correlations that are stronger than are classically possible without communication. Communication itself still cannot be achieved, by any sequence of measurements.
    - TrapLord_Rhodo 4y ago
      Taken from your wiki link with a twist; "spooky correlation at a distance" does seem to be some amount of information. The paul revere joke was entirely out of scope, but the universe does seem to have some way to pull the strings behind the curtain here.
deleted 4y ago
[deleted]
hsn915 4y ago
I don't care that you can't use it to communicate FTL. I care that the atoms are doing it or not.

kgwgk 4y ago

> Two contradictory talking points seem to be pervasive: They are not really contradictory. > - Altering one atom affects the other instantaniously It kind-of does, if by "affecting the other" you mean changing the physical state of the pair from "the A/B system is in state S0" to "A is in state SA and B is in state SB". > - There's no FTL communication going on, There isn't unless you want to define as "communication" the change in the physical state described above. > Basically, never take seriously anything written about quantum physics in pop-science magazines. That's unfortunately a wise advice.