"A European test has already proved that photons can remain entangled across a distance of almost 90 miles (144 km). Researchers entangled a pair of photons on the Canary Island of Tenerife in the Atlantic Ocean and beamed one of the entangled photons to a receiver station on the neighboring island of La Palma in September 2005."
I had no idea that there was already a proof-of-concept.
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posted
Thanks for the link, that's fascinating! I wonder if this is any faster than fiber optic cables, and what the data transfer rate is, or if this is really more about transmission security than it is about speed.
And also, hello Drummer, nice to meet you! Posts: 21898 | Registered: Nov 2004
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posted
Quantum entanglement does not allow faster than light communications regardless of how far apart the particles are. When you observe the state of one particle, the state of that particle (and thus it's entangled partner) is determined, but you can't actually select the state of the particle so no information has been transmitted.
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posted
It is faster than light (it is instantaneous, or as Uncle Albert put it, "spooky action at a distance").
However, it only works once. That is, once you measure an entangled photon, it can't be re-used.
Further, you still have to separate the two entangled photons the old fashioned way (no faster than the speed of light)
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posted
It's a faster than light phenomenon, but it's not faster than light communication because you cannot influence the state of the particle, only observe it (which causes a random state to be selected.)
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posted
As I said the last time somebody posted this: Sadly, causality means that 1+1 will always equal 2. Always. No matter what other weird crap you figure out.
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quote:Originally posted by MattP: Quantum entanglement does not allow faster than light communications regardless of how far apart the particles are. When you observe the state of one particle, the state of that particle (and thus it's entangled partner) is determined, but you can't actually select the state of the particle so no information has been transmitted.
Yes, but you can tell if a particular particle has been observed on the other end, right?
If you have an agreed-upon standard, and multiple particles to work with, then you can transmit information by selectively observing some particles and not others, right?
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quote:Yes, but you can tell if a particular particle has been observed on the other end, right?
No, you can't. How can you tell whether a particle's wave-function has collapsed? Except of course by measuring it yourself and causing the collapse, but that rather spoils the point.
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quote:Originally posted by King of Men: No, you can't. How can you tell whether a particle's wave-function has collapsed? Except of course by measuring it yourself and causing the collapse, but that rather spoils the point.
Then what's the evidence the two particles are actually entangled, if you can't tell what's happened with the particle in the distant location by checking your own particle?
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quote:Originally posted by I Used to Be a Drummer:
quote:Originally posted by King of Men: No, you can't. How can you tell whether a particle's wave-function has collapsed? Except of course by measuring it yourself and causing the collapse, but that rather spoils the point.
Then what's the evidence the two particles are actually entangled, if you can't tell what's happened with the particle in the distant location by checking your own particle?
Correlations in the measurements, compared after both sides have done them. Seriously, we keep telling you, there's no information transfer.
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quote:Originally posted by King of Men: Yep. The CERN neutrinos look a lot better in terms of FTL communication.
False. The apparent FTL neutrinos are a result of experimental error. Faulty fiber optic cable in the data acquisition resulted in a lot of garbage events that made it seem as though neutrinos were moving FTL.
posted
Yes, I know. They still look better than mere entanglement as a possible means of FTL communication.
Additionally, as your source points out, there were two errors; one which increased the apparent speed of the neutrinos, and one which reduced it. It is not yet clear which effect was the stronger.
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quote:Originally posted by King of Men: Correlations in the measurements, compared after both sides have done them. Seriously, we keep telling you, there's no information transfer.
So if there's no information transfer, how is entanglement useful for catching hackers?
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posted
BW, this is not a matter of technical expertise. That you can't select the state of a particle is a law of nature. It has no state until you measure it- you can't effect what that state will be because it won't have one until you know what it is.
Sort of like you have to build a car to win a race. No amount of technical achievement can allow you to win the race *before* you build the car.
As much as you'd like to say: "yeah well, but still, it has a state even if you haven't seen it," that is totally irrelevant. You can't effect a particle without finding out its state or position first- you can't interact with something about which you have no information.
Basically, the "technical know how," to accomplish such a feat would probably be equivalent to just changing the laws of nature to suit your purposes. Not possible. Not just beyond our capabilities.
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quote:So if there's no information transfer, how is entanglement useful for catching hackers?
If I understand it (and I don't have a lot of confidence in that), the discovery of eavesdropping only occurs via an exchange of data over conventional (sub-light) channels. You can't determine that tampering has occurred just by examining the particles at one end. So, again, no information has been transmitted faster than light.
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quote:As much as you'd like to say: "yeah well, but still, it has a state even if you haven't seen it," that is totally irrelevant.
It's not only irrelevant, it's also untrue. The particle doesn't have a particular state, it has a superposition of states.
quote:So if there's no information transfer, how is entanglement useful for catching hackers?
You are probably thinking of quantum key distribution. It relies sending information about the measurement basis in addition to the actual quantum bits. You can't do it with entangled bits alone; you have to check afterwards whether your bits were in fact entangled. If they weren't, you know something decohered them, but there's no way to check that without looking at the measurement result on both ends. In other words, you're limited to lightspeed.
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quote:Originally posted by King of Men: You are probably thinking of quantum key distribution. It relies sending information about the measurement basis in addition to the actual quantum bits. You can't do it with entangled bits alone; you have to check afterwards whether your bits were in fact entangled. If they weren't, you know something decohered them, but there's no way to check that without looking at the measurement result on both ends. In other words, you're limited to lightspeed.
OK. The original article didn't exactly make that clear.
To be fair, I'm not sure many journalists, even science journalists, understand quantum physics well enough to know this.
Well, maybe journalists who work for Scientific American, etc., might know, but InnovationNewsDaily is not exactly Scientific American.
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quote:Originally posted by Orincoro: BW, this is not a matter of technical expertise.
...equivalent to just changing the laws of nature to suit your purposes. Not possible. Not just beyond our capabilities.
Everything is Magic ... until it is not.
It was impossible to fly ... until we flew.
It was impossible to sustain speeds of 60mph ... until we did.
It was impossible to run a 4 minute mile ... until we did.
Everything is impossible ... until it's not.
These Quantum Entanglements may not be the solution, but they might be the seed that leads to the solution.
Science fiction is fiction ... until it is not.
Steve/bluewizard
Aside from the fact that these are all mythical beliefs that were not actually seriously held by scientists... (read: perhaps held by philosophers millennia ago- *perhaps*) you're still not getting the picture.
Each of these accomplishments represents a gradation of ability, built upon a foundation that it was (at one time) believed would never reach X goal. Not because it was strictly impossible, but because it was practically impossible at the time.
What you suggest is a violation not of the limits of engineering or athletics, as these others were, but of the laws of the universe. Leonardo could imagine a machine that flew centuries before one did, because he knew that all that was necessary was the material science to achieve the goal. Birds fly. Humans were aware that this was a practical matter that begged a solution, ever since they gave of the notion of the plutonic ether.
The 60mph thing is pure hokum.
The 4 minute mile was a matter of training and nutrition. Again, a gradation. If you can run a mile in 5 minutes, the "impossibility" of running one in 4 is a practical matter- not one that involves the laws of the universe. You're way off base with this comparison.
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posted
Why argue about it? If you think it can be done, off you go and do it. If not, do something else. Until there's money or effort riding on it, what does it matter?
I point out in passing that nobody educated in the matter has any money invested in make-the-collapse-happen research, any more than in perpetual-motion engines. But no doubt you can find someone who promises to produce results in a year or two. Don't spend all your money with the one charlatan, now.
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