5 ms·

Nothing new here, just a demonstration of stuff we've known for years on a somewhat more spectacular length scale. The editors of Nature should know better tha

by hugh 18y ago

Nothing new here, just a demonstration of stuff we've known for years on a somewhat more spectacular length scale. The editors of Nature should know better than to put a headline like "faster-than-light information transfer" on there, since that is exactly what isn't going on. It's a shame that the article didn't make any mention of the "many-worlds" interpretation of QM (I don't like that term myself) which as far as I know is the only explanation for these results which makes any sense.

lisper 18y ago
http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf
biohacker42 18y ago
Couldn't you measure the state of the entangled pair and record it? Then take one particle and walk it over the next village. Assume Bob and Alice have both agreed to look at their particles every 3 seconds. If the state changes relative to the last state, that's a 1. If you see the same state twice, that's a 0. So would that be 1 bit of information every 6 seconds, or am I totally screwing up the quantum reverse tachion stream?
- lacker 18y ago
  No. Once you measure it, it is no longer entangled. Also, you cannot set the state to whatever you want. You can only measure different properties of the particles. It doesn't really make sense. Think of it as, there's probably something really intuitive happening, but physicists haven't figured that out yet. Instead we only have really complicated formulas and unintuitive metaphors. So don't think that necessarily things "really change" when you measure them. That's just the simplest assumption we have right now that makes the formulas workable.
  - ericb 18y ago
    >> Once you measure it, it is no longer entangled. I was struggling to figure out how this wouldn't be useful for communication. That was the piece I was missing. Thank-you.
  - lisper 18y ago
    > Once you measure it, it is no longer entangled. This is not true. If it were then FTL communication would be possible. See http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf
andreyf 18y ago
The editors of Nature should know better than to put a headline like "faster-than-light information transfer" on there, since that is exactly what isn't going on. Um, this part seems to imply so... "the researchers found that when each photon reached its destination [some 18 kilometres apart], it could instantly sense its twin’s behaviour without any direct communication."
- lacker 18y ago
  The key is, this "sensing its twin's behavior" only works if you interfere with the twin in a randomized way. You can't set one particle to a 0 bit and have the other one sense it. So you can't use this for sending information. It's hard to explain this in the space of a comment. You might try Wikipedia - http://en.wikipedia.org/wiki/Quantum_entanglement http://en.wikipedia.org/wiki/Quantum_entanglement
- Retric 18y ago
  Think of ‘entangled’ photons as sharing a secret. If either one gives up that secret than you also know what the other one is doing. The only spooky part they don't behave like they have a specific value until you measure it and you can randomly change it's value. PS: You can't send information from a to b using two ‘entangled’ photons sent from c and read at a and b.
glymor 18y ago
How is many-worlds a scientific theory ie how is it testable?
- lacker 18y ago
  It's more like, right now we have two rather bad explanations for basic quantum mechanics. There is the "particles change when a human measures them" explanation, and there is the "there are many worlds and we can usually only observe one" explanation. They both explain the same set of formulas that have been verified many times by experiment. Depending on what you want to do with the theory, it may be more intuitive to use one formulation than the other. Hopefully at some point in the future it becomes obvious that one of the formulations lacks the explanatory power of the other, and then scientists can cohere on one. Like epicycles as a scientific explanation of how the sun revolves around the earth. Somewhat off topic but interesting reading - http://en.wikipedia.org/wiki/Deferent_and_epicycle http://en.wikipedia.org/wiki/Deferent_and_epicycle
  - Herring 18y ago
    You're thinking about it wrong. Start from Bell's theorem - it tells us we have to sacrifice locality or realism. MWI weasels out of it by making worlds be observer dependent, basically splitting the observer up. Bell's theorem is the root. It's not an interpretation & all interpretations come from it.
- gaika 18y ago
  Many worlds is testable, though I wouldn't recommend it: http://en.wikipedia.org/wiki/Quantum_suicide http://en.wikipedia.org/wiki/Quantum_suicide Edit: :)
  - hugh 18y ago
    I don't buy quantum immortality as a necessary consequence of many-worlds. There are some rather dodgy steps in the logic -- in particular the one that says that "you" can't find your personal experiences going down a branch where your existence gets terminated. Surely somebody has to be there to subjectively experience having a bullet blast a hole in their skull? Personally I think if you tried that, even if many-worlds is true, you'd almost certainly wind up dead.
bentoner 18y ago
There is definitely something new here, although the linked article does obscure what this is---read the actual paper or see my other comment. Why do you think there is an important connection to many-worlds? Many-worlds is an interpretation of quantum theory: the experiment tests quantum theory itself, independent of your interpretation.
- hugh 18y ago
  You're right, now I come to read more carefully there is something new here -- it's a more convincing test than has been done before. The experimental setup is neat -- by setting up the detectors along an east-west axis and using the Earth's rotation, they can show that there isn't some "special" frame of reference in which the particles are communicating. Very neat experiment.
ars 18y ago
I agree there is nothing new here except the length. The many worlds explanation does not help for this. That explanation is only useful for dealing with quantum interference. Many worlds does not explain why the two photons give related results. A theory that can explain it is the hidden variables theory (which makes a lot of sense to me, because I can't understand the bell inequality). It has still not been ruled out, although the gut feeling is that it's not happening. I have another option: the two photons are hard linked in the matrix simulator of the universe. That would explain it pretty nicely no? The planck length is the size of each cell in the simulation. All the various quanta (and there are some really weird ones, like direction) are because that's the smallest increment in the variables that keep track of each cell. Anyone know a good hacker? I want root access :)
davidmathers 18y ago
"The editors of Nature should know better than to put a headline like "faster-than-light information transfer" on there, since that is exactly what isn't going on." Totally. The article even contains this sentence: "In other words, these photons cannot know about each other through any sort of normal exchange of information." Very very disappointing.
rms 18y ago
>which makes any sense. Luttgeinstein/Chomsky blah blah blah. Who says nature is supposed to make any sense? Our "sense" is an artificial construct of the thoughts we are capable of thinking, limited by our inadequate brains and even more inadequate language. Having said that my money is also on many-worlds, because it is the only one that makes sense.
- netcan 18y ago
  Well, seems to make more sense then separating observers from the universe.
rms 18y ago
>The conclusion was that the minimal speed of hypothetical spooky action at a distance, under plausible assumptions for this experiment, is at least 10,000 times greater than the speed of light.

by hugh 18y ago

lisper 18y ago

http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf

biohacker42 18y ago

Couldn't you measure the state of the entangled pair and record it? Then take one particle and walk it over the next village. Assume Bob and Alice have both agreed to look at their particles every 3 seconds. If the state changes relative to the last state, that's a 1. If you see the same state twice, that's a 0. So would that be 1 bit of information every 6 seconds, or am I totally screwing up the quantum reverse tachion stream?

lacker 18y ago
No. Once you measure it, it is no longer entangled. Also, you cannot set the state to whatever you want. You can only measure different properties of the particles. It doesn't really make sense. Think of it as, there's probably something really intuitive happening, but physicists haven't figured that out yet. Instead we only have really complicated formulas and unintuitive metaphors. So don't think that necessarily things "really change" when you measure them. That's just the simplest assumption we have right now that makes the formulas workable.
- ericb 18y ago
  >> Once you measure it, it is no longer entangled. I was struggling to figure out how this wouldn't be useful for communication. That was the piece I was missing. Thank-you.
- lisper 18y ago
  > Once you measure it, it is no longer entangled. This is not true. If it were then FTL communication would be possible. See http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf

andreyf 18y ago

The editors of Nature should know better than to put a headline like "faster-than-light information transfer" on there, since that is exactly what isn't going on. Um, this part seems to imply so... "the researchers found that when each photon reached its destination [some 18 kilometres apart], it could instantly sense its twin’s behaviour without any direct communication."

lacker 18y ago
The key is, this "sensing its twin's behavior" only works if you interfere with the twin in a randomized way. You can't set one particle to a 0 bit and have the other one sense it. So you can't use this for sending information. It's hard to explain this in the space of a comment. You might try Wikipedia - http://en.wikipedia.org/wiki/Quantum_entanglement http://en.wikipedia.org/wiki/Quantum_entanglement
Retric 18y ago
Think of ‘entangled’ photons as sharing a secret. If either one gives up that secret than you also know what the other one is doing. The only spooky part they don't behave like they have a specific value until you measure it and you can randomly change it's value. PS: You can't send information from a to b using two ‘entangled’ photons sent from c and read at a and b.

glymor 18y ago

How is many-worlds a scientific theory ie how is it testable?

lacker 18y ago
It's more like, right now we have two rather bad explanations for basic quantum mechanics. There is the "particles change when a human measures them" explanation, and there is the "there are many worlds and we can usually only observe one" explanation. They both explain the same set of formulas that have been verified many times by experiment. Depending on what you want to do with the theory, it may be more intuitive to use one formulation than the other. Hopefully at some point in the future it becomes obvious that one of the formulations lacks the explanatory power of the other, and then scientists can cohere on one. Like epicycles as a scientific explanation of how the sun revolves around the earth. Somewhat off topic but interesting reading - http://en.wikipedia.org/wiki/Deferent_and_epicycle http://en.wikipedia.org/wiki/Deferent_and_epicycle
- Herring 18y ago
  You're thinking about it wrong. Start from Bell's theorem - it tells us we have to sacrifice locality or realism. MWI weasels out of it by making worlds be observer dependent, basically splitting the observer up. Bell's theorem is the root. It's not an interpretation & all interpretations come from it.
gaika 18y ago
Many worlds is testable, though I wouldn't recommend it: http://en.wikipedia.org/wiki/Quantum_suicide http://en.wikipedia.org/wiki/Quantum_suicide Edit: :)
- hugh 18y ago
  I don't buy quantum immortality as a necessary consequence of many-worlds. There are some rather dodgy steps in the logic -- in particular the one that says that "you" can't find your personal experiences going down a branch where your existence gets terminated. Surely somebody has to be there to subjectively experience having a bullet blast a hole in their skull? Personally I think if you tried that, even if many-worlds is true, you'd almost certainly wind up dead.

bentoner 18y ago

There is definitely something new here, although the linked article does obscure what this is---read the actual paper or see my other comment. Why do you think there is an important connection to many-worlds? Many-worlds is an interpretation of quantum theory: the experiment tests quantum theory itself, independent of your interpretation.

hugh 18y ago
You're right, now I come to read more carefully there is something new here -- it's a more convincing test than has been done before. The experimental setup is neat -- by setting up the detectors along an east-west axis and using the Earth's rotation, they can show that there isn't some "special" frame of reference in which the particles are communicating. Very neat experiment.

ars 18y ago

I agree there is nothing new here except the length. The many worlds explanation does not help for this. That explanation is only useful for dealing with quantum interference. Many worlds does not explain why the two photons give related results. A theory that can explain it is the hidden variables theory (which makes a lot of sense to me, because I can't understand the bell inequality). It has still not been ruled out, although the gut feeling is that it's not happening. I have another option: the two photons are hard linked in the matrix simulator of the universe. That would explain it pretty nicely no? The planck length is the size of each cell in the simulation. All the various quanta (and there are some really weird ones, like direction) are because that's the smallest increment in the variables that keep track of each cell. Anyone know a good hacker? I want root access :)

davidmathers 18y ago

"The editors of Nature should know better than to put a headline like "faster-than-light information transfer" on there, since that is exactly what isn't going on." Totally. The article even contains this sentence: "In other words, these photons cannot know about each other through any sort of normal exchange of information." Very very disappointing.

rms 18y ago

>which makes any sense. Luttgeinstein/Chomsky blah blah blah. Who says nature is supposed to make any sense? Our "sense" is an artificial construct of the thoughts we are capable of thinking, limited by our inadequate brains and even more inadequate language. Having said that my money is also on many-worlds, because it is the only one that makes sense.

netcan 18y ago
Well, seems to make more sense then separating observers from the universe.

rms 18y ago

>The conclusion was that the minimal speed of hypothetical spooky action at a distance, under plausible assumptions for this experiment, is at least 10,000 times greater than the speed of light.