7 ms·

You can’t get entangled without a wormhole (2013)

93 points by saurabh 12y ago

orbifold 12y ago
This is pointed out in the research article, but the overall idea that matter-antimatter pairs created in the vacuum are connected by a wormhole is due to Wheeler. The twist here is that the result is obtained by applying ADS-CFT duality first, so the calculation is done in a 5 dimensional gravitational theory. A more accurate statement would be that under ADS-CFT an entangled particle state in 4 dimensions probably can be modelled as a wormhole in the gravity dual, which is not entirely surprising.
mef51 12y ago
The paper: http://arxiv.org/pdf/1307.6850v3.pdf http://arxiv.org/pdf/1307.6850v3.pdf
dools 12y ago
When I watched the Leonard Susskind lectures on quantum entanglements he said the whole "communicating faster than light" thing is a bit misleading. The analogy he gives if imagine you have two coins and you ask someone to turn them over so one is heads and the other tails then you give them to 2 people without them knowing which is which, then they go to opposite ends of the universe, and they look at their coins, they instantly know the state of the other coin purely by deduction.
- hasenj 12y ago
  That's what Einstein argued for, and it's what Bell's inequality proves to not be the case. I actually remember seeing a Youtube video of Susskind talking about how "FTL" communication is a hack to try to force the quantum state to conform with our notions about the world. (he didn't phrase it this way though; just my interpretation). I don't know the context it was said, but it seemed to imply that there's a way of thinking about quantum states completely independent of set theory and our classical notions, and this way of thinking should not require FTL communication between entangled particles. Edit: I think this was the video: https://www.youtube.com/watch?v=xT1bm1yM8Ow https://www.youtube.com/watch?v=xT1bm1yM8Ow He seems to imply that Aspect's experiment negates hidden/FTL communication.
  - evanb 12y ago
    While GP's example is not what happens in QM (Bell's inequality shows that the state of the two coins is not predetermined-but-secret), it is akin to that example, in the sense that because each person gets a random (though correlated) bit, they cannot transmit information to one another. Bell's inequality is a statement about the possible strength of the correlation, rather than about information transmission.
    - pfortuny 12y ago
      Exactly. It is important to note that there is no information exchange if you do not have any information at all. BTW: why did internet explorer just capitalize Exchange without my asking?
      - ep103 12y ago
        spell check, exchange is a microsoft product.
- chm 12y ago
  The difference with entangled particles is that you produce them, don't look at them, and ship them out of the lab. Both particles are initially quantum mechanically identical, in a superposition state, which becomes definite only upon measurement. The coin analogy supports a hidden variable theory, in that the measurement uncertainty isn't due to a fundamental limitation of nature but to the experimenter's lack of knowledge about the system. If that analogy was correct, one could simply send a piece of paper with the result of the measurement along with Alice OR Bob's "entangled" particle and make Alive OR Bob verify the assertion by taking a measurement. But then, that's not entanglement. Coin flips obey classical probability laws. Quantum mechanical particles don't. Coin flip probabilities don't interfere.
  - ealloc 12y ago
    I think the parent is talking about a response to this point of view. Historically, people first wondered whether QM could be explained by hidden variables. Then they proved it could not, which seemed to imply "spooky action at a distance". But now, Susskind is arguing that actually the logic of the 'hidden variable' gives the right intuition, even though there isn't actually a hidden variable. Here's how I have come to think of it: When you create the two opposite-spin particles and send them to opposite ends of the galaxy, they exist in a superposition of states which follows QM probabilities. The spins are anti-aligned in all of these possible states , but pointing in a different direction in each state. When one person observes his/her particle, you can imagine it's like they are 'masking out' many of the possible states, leaving just one of the possible "universes". But no matter which "universe" gets masked out, in the "surviving universe" the spins are going to be anti-aligned. This is a lot like the 'hidden variable' picture where the spins were pre-decided and put into boxes, and when person A opened her box and saw "up" she knew that the other person must have the "down" spin. The difference is that QM probabilities are not consistent with the probabilities you would get from such a boxing procedure (in particular when the observers measure the spin at different angles). But conceptually, opening the box and realizing that you have the "up" spin and therefore the other person has down is a lot like doing a spin measurement and masking out many of the superpositions, and concluding that the other person must have the opposite spin from what you measured.
- deciplex 12y ago
  Isn't entanglement, more like you take the coins to opposite ends of the universe, and then by flipping one and observing the result, you know what the result will be when the other one is flipped? The whole point of entanglement is that the state of the entangled particles isn't determined yet, until observed, which is not the case with the coin example. http://en.wikipedia.org/wiki/Bell%27s_theorem http://en.wikipedia.org/wiki/Bell%27s_theorem
- ninkendo 12y ago
  From what I've read, the rub is that you don't know which side of the coin the current one is until you observe it, and only at the exact time of observation does the other coin assume the other state. Apparently, the point at which you observe the one coin is called the collapse of the wave function, and we have ways of directly measuring that the collapse doesn't happen until one of the particles is observed. (But it's never been too clear to me how that's possible... if observing a particle collapses the wave function, how do we observe when the collapse happens, without first observing the particle?)
  - nitrogen 12y ago
    It sounds like the universe may be built on lazy expression evaluation.
  - Jach 12y ago
    The problem with the 'collapse' point of view is that it's easy to say "and thus only the observation we saw actually exists". But that's an extra postulate beyond asserting the wavefunction describes all of reality. By just saying the wavefunction describes all of reality, you wind up with Many-worlds: http://en.wikipedia.org/wiki/Many-worlds_interpretation http://en.wikipedia.org/wiki/Many-worlds_interpretation So the coins/paper analogies do make sense, except that there's not a single outcome: there are two possible outcomes, both realized, but each version of you interacting ("observing" is a loaded term) with the system to the point of decoherence (http://en.wikipedia.org/wiki/Quantum_decoherence http://en.wikipedia.org/wiki/Quantum_decoherence) only ever get to see one of the worlds, which is the one you find yourself in. This isn't that mysterious given that your brain and everything else in your body are made of the same fundamental particles as everything else. You highlighted a problem with quantum computers and other things: how to make sure a system is in a quantum state without directly measuring it. It's hard to fight decoherence.
  - plesner 12y ago
    A little rusty on my QM but I believe the key to demonstrating when the collapse happens is that while doing a measurement will collapse the wave function, applying a transformation won't necessarily. An experiment can work something like this. Produce 1000 state that you think are undecided. Apply a transformation that you know will turn the uncollapsed 50/50 state to 1 and the collapsed 0 and 1 states to the uncollapsed 50/50 state. Then measure all 1000 states. If they all yield 1, with high probability they were were indeed undecided to begin with. If they yield random results, with high probability they were collapsed 0 or 1 to begin with.
- bo1024 12y ago
  This is a pretty good analogy for explaining why "communication" is the wrong term. It does get wrong the hidden variable thing, which others are pointing out. A better analogy would be like I create a pair of coins one of which only turns up heads and the other only turns up tails, but you can't tell which is which until you flip them, and I put them in a bag and they each draw one, travel apart, flip, and deduce. But this is still wrong because the coins had their true state "inside" them the whole time. The part about quantum probability comes in where the coins don't decide which one of them is which until they are flipped (but they decide together, consistently).
- Beltiras 12y ago
  The thing about quantum physics according to Feynman is that quantum objects do not behave in any way like macroscopic objects. You can't use analogies that are rooted in the scale we observe.
pistle 12y ago
Stop stop stop saying "communicating at a distance." They may be formed or placed into an "entangled" state, but they aren't communicating through any physical wormhole. It's waves all the way down. And string theory? Someone pass the arxiv...
atilev 12y ago
if this is validated it might be the single most important piece of proof in our lives we just don't know it yet...
deleted 12y ago
[deleted]
sideshowb 12y ago
Like everyone else here says, entanglement doesn't give rise to FTL communication. So can someone explain to me how this paper even exists / has anything to explain via wormholes?

93 points by saurabh 12y ago

This is pointed out in the research article, but the overall idea that matter-antimatter pairs created in the vacuum are connected by a wormhole is due to Wheeler. The twist here is that the result is obtained by applying ADS-CFT duality first, so the calculation is done in a 5 dimensional gravitational theory. A more accurate statement would be that under ADS-CFT an entangled particle state in 4 dimensions probably can be modelled as a wormhole in the gravity dual, which is not entirely surprising.

mef51 12y ago

The paper: http://arxiv.org/pdf/1307.6850v3.pdf http://arxiv.org/pdf/1307.6850v3.pdf

dools 12y ago

When I watched the Leonard Susskind lectures on quantum entanglements he said the whole "communicating faster than light" thing is a bit misleading. The analogy he gives if imagine you have two coins and you ask someone to turn them over so one is heads and the other tails then you give them to 2 people without them knowing which is which, then they go to opposite ends of the universe, and they look at their coins, they instantly know the state of the other coin purely by deduction.

hasenj 12y ago
That's what Einstein argued for, and it's what Bell's inequality proves to not be the case. I actually remember seeing a Youtube video of Susskind talking about how "FTL" communication is a hack to try to force the quantum state to conform with our notions about the world. (he didn't phrase it this way though; just my interpretation). I don't know the context it was said, but it seemed to imply that there's a way of thinking about quantum states completely independent of set theory and our classical notions, and this way of thinking should not require FTL communication between entangled particles. Edit: I think this was the video: https://www.youtube.com/watch?v=xT1bm1yM8Ow https://www.youtube.com/watch?v=xT1bm1yM8Ow He seems to imply that Aspect's experiment negates hidden/FTL communication.
- evanb 12y ago
  While GP's example is not what happens in QM (Bell's inequality shows that the state of the two coins is not predetermined-but-secret), it is akin to that example, in the sense that because each person gets a random (though correlated) bit, they cannot transmit information to one another. Bell's inequality is a statement about the possible strength of the correlation, rather than about information transmission.
  - pfortuny 12y ago
    Exactly. It is important to note that there is no information exchange if you do not have any information at all. BTW: why did internet explorer just capitalize Exchange without my asking?
    - ep103 12y ago
      spell check, exchange is a microsoft product.
chm 12y ago
The difference with entangled particles is that you produce them, don't look at them, and ship them out of the lab. Both particles are initially quantum mechanically identical, in a superposition state, which becomes definite only upon measurement. The coin analogy supports a hidden variable theory, in that the measurement uncertainty isn't due to a fundamental limitation of nature but to the experimenter's lack of knowledge about the system. If that analogy was correct, one could simply send a piece of paper with the result of the measurement along with Alice OR Bob's "entangled" particle and make Alive OR Bob verify the assertion by taking a measurement. But then, that's not entanglement. Coin flips obey classical probability laws. Quantum mechanical particles don't. Coin flip probabilities don't interfere.
- ealloc 12y ago
  I think the parent is talking about a response to this point of view. Historically, people first wondered whether QM could be explained by hidden variables. Then they proved it could not, which seemed to imply "spooky action at a distance". But now, Susskind is arguing that actually the logic of the 'hidden variable' gives the right intuition, even though there isn't actually a hidden variable. Here's how I have come to think of it: When you create the two opposite-spin particles and send them to opposite ends of the galaxy, they exist in a superposition of states which follows QM probabilities. The spins are anti-aligned in all of these possible states , but pointing in a different direction in each state. When one person observes his/her particle, you can imagine it's like they are 'masking out' many of the possible states, leaving just one of the possible "universes". But no matter which "universe" gets masked out, in the "surviving universe" the spins are going to be anti-aligned. This is a lot like the 'hidden variable' picture where the spins were pre-decided and put into boxes, and when person A opened her box and saw "up" she knew that the other person must have the "down" spin. The difference is that QM probabilities are not consistent with the probabilities you would get from such a boxing procedure (in particular when the observers measure the spin at different angles). But conceptually, opening the box and realizing that you have the "up" spin and therefore the other person has down is a lot like doing a spin measurement and masking out many of the superpositions, and concluding that the other person must have the opposite spin from what you measured.
deciplex 12y ago
Isn't entanglement, more like you take the coins to opposite ends of the universe, and then by flipping one and observing the result, you know what the result will be when the other one is flipped? The whole point of entanglement is that the state of the entangled particles isn't determined yet, until observed, which is not the case with the coin example. http://en.wikipedia.org/wiki/Bell%27s_theorem http://en.wikipedia.org/wiki/Bell%27s_theorem
ninkendo 12y ago
From what I've read, the rub is that you don't know which side of the coin the current one is until you observe it, and only at the exact time of observation does the other coin assume the other state. Apparently, the point at which you observe the one coin is called the collapse of the wave function, and we have ways of directly measuring that the collapse doesn't happen until one of the particles is observed. (But it's never been too clear to me how that's possible... if observing a particle collapses the wave function, how do we observe when the collapse happens, without first observing the particle?)
- nitrogen 12y ago
  It sounds like the universe may be built on lazy expression evaluation.
- Jach 12y ago
  The problem with the 'collapse' point of view is that it's easy to say "and thus only the observation we saw actually exists". But that's an extra postulate beyond asserting the wavefunction describes all of reality. By just saying the wavefunction describes all of reality, you wind up with Many-worlds: http://en.wikipedia.org/wiki/Many-worlds_interpretation http://en.wikipedia.org/wiki/Many-worlds_interpretation So the coins/paper analogies do make sense, except that there's not a single outcome: there are two possible outcomes, both realized, but each version of you interacting ("observing" is a loaded term) with the system to the point of decoherence (http://en.wikipedia.org/wiki/Quantum_decoherence http://en.wikipedia.org/wiki/Quantum_decoherence) only ever get to see one of the worlds, which is the one you find yourself in. This isn't that mysterious given that your brain and everything else in your body are made of the same fundamental particles as everything else. You highlighted a problem with quantum computers and other things: how to make sure a system is in a quantum state without directly measuring it. It's hard to fight decoherence.
- plesner 12y ago
  A little rusty on my QM but I believe the key to demonstrating when the collapse happens is that while doing a measurement will collapse the wave function, applying a transformation won't necessarily. An experiment can work something like this. Produce 1000 state that you think are undecided. Apply a transformation that you know will turn the uncollapsed 50/50 state to 1 and the collapsed 0 and 1 states to the uncollapsed 50/50 state. Then measure all 1000 states. If they all yield 1, with high probability they were were indeed undecided to begin with. If they yield random results, with high probability they were collapsed 0 or 1 to begin with.
bo1024 12y ago
This is a pretty good analogy for explaining why "communication" is the wrong term. It does get wrong the hidden variable thing, which others are pointing out. A better analogy would be like I create a pair of coins one of which only turns up heads and the other only turns up tails, but you can't tell which is which until you flip them, and I put them in a bag and they each draw one, travel apart, flip, and deduce. But this is still wrong because the coins had their true state "inside" them the whole time. The part about quantum probability comes in where the coins don't decide which one of them is which until they are flipped (but they decide together, consistently).
Beltiras 12y ago
The thing about quantum physics according to Feynman is that quantum objects do not behave in any way like macroscopic objects. You can't use analogies that are rooted in the scale we observe.

pistle 12y ago

Stop stop stop saying "communicating at a distance." They may be formed or placed into an "entangled" state, but they aren't communicating through any physical wormhole. It's waves all the way down. And string theory? Someone pass the arxiv...

atilev 12y ago

if this is validated it might be the single most important piece of proof in our lives we just don't know it yet...

deleted 12y ago

[deleted]

sideshowb 12y ago

Like everyone else here says, entanglement doesn't give rise to FTL communication. So can someone explain to me how this paper even exists / has anything to explain via wormholes?