5 ms·

Because once the particles are entangled, one has to be moved by conventional means to the destination while the other stays behind.

dbingham 8y ago
Sure, but you could still create a two way walkie talkie that couldn't be eavesdropped on and would allow faster than light communication this way, theoretically.
- simcop2387 8y ago
  You can make it secure from mitm with this but it doesn't allow ftl. You can't use the entangled particles themselves to do the communication since you cant control how the superposition collapses when you measure it. This allows you to get two streams that nobody but you and the party knows but they're fundamentally random and unpredictable, you can't encoded information into it, just use it as a one time pad essentially.
  - bduerst 8y ago
    But that in itself is a signal, right? Say you have two sets of two entangled particles, all four particles in similar states. You have one particle from each set, your partner has the corresponding particles in the sets. You check both particles you have, and: - if both particles have similar state, then your partner hasn't checked any of their particle states, because neither have collapsed. - if one particle has collapsed and is in a different state than the other particle, then you know your partner has at least checked the state of one of particle sets, possibly both. If you partner is 50 light years away and checks it only seconds prior to your check, then they are signalling you at faster-than-light travel, right?
    - danielsju6 8y ago
      But you have to communicate the states of each other's particles (as far as you can tell random noise) to compare/contrast and glean influence, so it's only suitable for encryption of classically transmitted messages. Think faster-than-light XOR ;)
      - bduerst 8y ago
        Got it, so the state is random for all particles until it is measured by your or your partner, afterwhich the other particle state is known. But the act of measuring or the decaying doesn't tell you when (or if) they measured it because the state never changes, it just becomes known.
        int_19h 8y ago
        It's not random; it's a superposition. It is perhaps less nonsensical (in a "common sense" way) to think of it in terms of the many-worlds interpretation. The moment you have created the photons, you have forked the universe - but observers on both sides are still identical in both worlds, because they haven't done anything that'd allow them to figure out which universe they're in. So for each observer, we treat both "versions" of that observer as one and the same. Now, when one of the observers measures their photon, they figure out which fork they're in. And then in that universe, the other observer measuring it will also get the same result, of course, proving that they're also in that same universe. And in the other universe, the second observer will get the opposite result, again, proving that they're in that other universe. But neither measurement actually caused anything to happen, nor did they get any information about the opposite observer in their universe as a result of it.
- jerf 8y ago
  abdullahkhalids has the correct answer. Even if you have the entangled particles already in place, you can't communicate with them. The real proof is that if you could, we'd already have this technology and high-speed traders would already be using it. If it could exist, we have all the tools to build it; it's far simpler than even a 4-qubit quantum computer, which we've also built. We don't have it because entanglement can't be used that way.
- semi-extrinsic 8y ago
  Nope, you couldn't. From all the experiments and theory we have on entanglement, you can't use it to communicate faster than light.
SigmundA 8y ago
Which is still extremely useful for things like probes. Instant comm's to Mars rover or even voyager. Of course no ones figured out how to make use of entanglement for information transfer. Pops up a lot in Sci-Fi, reading Three-Bodied Problem now and the aliens sent "sophons" basically probes the size of protons at near the speed of light to earth from Alpha Centauri, they arrived in a few years while their invasion fleet will take 400 years to get here. The sophons spy and interfere with earth communicating with aliens via quantum entanglement.
- teraflop 8y ago
  > Of course no ones figured out how to make use of entanglement for information transfer. Saying "no one's figured it out" is misleading because it creates the impression that it's an engineering problem to be solved. According to our best understanding of quantum mechanics, the laws of physics fundamentally do not permit faster-than-light communication, whether through entanglement or any other mechanism.
  - Filligree 8y ago
    Well, of course they don't. How would you even begin to build a simulator for something like that? Communications overhead between the nodes is bad enough as it is.
  - SigmundA 8y ago
    I was trying to imply that its probably the best avenue for research, and also we may never figure it out, might be a dead end. However I would say the reason it is used so much in sci-fi is it currently the one way we can cause action at a distance faster than light, which is so tantalizingly close to communication.
    - codethief 8y ago
      I wouldn't say we're close to FTL transfer of information in any meaningful way. In particular, > we can cause action at a distance is not true, either.

dbingham 8y ago

Sure, but you could still create a two way walkie talkie that couldn't be eavesdropped on and would allow faster than light communication this way, theoretically.

simcop2387 8y ago
You can make it secure from mitm with this but it doesn't allow ftl. You can't use the entangled particles themselves to do the communication since you cant control how the superposition collapses when you measure it. This allows you to get two streams that nobody but you and the party knows but they're fundamentally random and unpredictable, you can't encoded information into it, just use it as a one time pad essentially.
- bduerst 8y ago
  But that in itself is a signal, right? Say you have two sets of two entangled particles, all four particles in similar states. You have one particle from each set, your partner has the corresponding particles in the sets. You check both particles you have, and: - if both particles have similar state, then your partner hasn't checked any of their particle states, because neither have collapsed. - if one particle has collapsed and is in a different state than the other particle, then you know your partner has at least checked the state of one of particle sets, possibly both. If you partner is 50 light years away and checks it only seconds prior to your check, then they are signalling you at faster-than-light travel, right?
  - danielsju6 8y ago
    But you have to communicate the states of each other's particles (as far as you can tell random noise) to compare/contrast and glean influence, so it's only suitable for encryption of classically transmitted messages. Think faster-than-light XOR ;)
    - bduerst 8y ago
      Got it, so the state is random for all particles until it is measured by your or your partner, afterwhich the other particle state is known. But the act of measuring or the decaying doesn't tell you when (or if) they measured it because the state never changes, it just becomes known.
      - int_19h 8y ago
        It's not random; it's a superposition. It is perhaps less nonsensical (in a "common sense" way) to think of it in terms of the many-worlds interpretation. The moment you have created the photons, you have forked the universe - but observers on both sides are still identical in both worlds, because they haven't done anything that'd allow them to figure out which universe they're in. So for each observer, we treat both "versions" of that observer as one and the same. Now, when one of the observers measures their photon, they figure out which fork they're in. And then in that universe, the other observer measuring it will also get the same result, of course, proving that they're also in that same universe. And in the other universe, the second observer will get the opposite result, again, proving that they're in that other universe. But neither measurement actually caused anything to happen, nor did they get any information about the opposite observer in their universe as a result of it.
jerf 8y ago
abdullahkhalids has the correct answer. Even if you have the entangled particles already in place, you can't communicate with them. The real proof is that if you could, we'd already have this technology and high-speed traders would already be using it. If it could exist, we have all the tools to build it; it's far simpler than even a 4-qubit quantum computer, which we've also built. We don't have it because entanglement can't be used that way.
semi-extrinsic 8y ago
Nope, you couldn't. From all the experiments and theory we have on entanglement, you can't use it to communicate faster than light.

SigmundA 8y ago

Which is still extremely useful for things like probes. Instant comm's to Mars rover or even voyager. Of course no ones figured out how to make use of entanglement for information transfer. Pops up a lot in Sci-Fi, reading Three-Bodied Problem now and the aliens sent "sophons" basically probes the size of protons at near the speed of light to earth from Alpha Centauri, they arrived in a few years while their invasion fleet will take 400 years to get here. The sophons spy and interfere with earth communicating with aliens via quantum entanglement.

teraflop 8y ago
> Of course no ones figured out how to make use of entanglement for information transfer. Saying "no one's figured it out" is misleading because it creates the impression that it's an engineering problem to be solved. According to our best understanding of quantum mechanics, the laws of physics fundamentally do not permit faster-than-light communication, whether through entanglement or any other mechanism.
- Filligree 8y ago
  Well, of course they don't. How would you even begin to build a simulator for something like that? Communications overhead between the nodes is bad enough as it is.
- SigmundA 8y ago
  I was trying to imply that its probably the best avenue for research, and also we may never figure it out, might be a dead end. However I would say the reason it is used so much in sci-fi is it currently the one way we can cause action at a distance faster than light, which is so tantalizingly close to communication.
  - codethief 8y ago
    I wouldn't say we're close to FTL transfer of information in any meaningful way. In particular, > we can cause action at a distance is not true, either.