I always wondered how Kirk was able to 'hail' ships a few light years away

News :

ESA takes steps toward quantum communications
http://www.esa.int/esaCP/SEMXM7Q08ZE_index_0.html
here's more on quantum physics, ftl and entanglement

Quantum entanglement
http://www.mtnmath.com/whatrh/node73.html
Spooky Atomic Clocks
http://science.nasa.gov/headlines/y2..._entangled.htm
New experiments with quantum entanglement suggest that reality might be overrated
http://arstechnica.com/journals/scie...t-be-overrated
Intercontinental quantum liaisons between entangled electrons in ion traps of thermoluminescent crystals
http://www.arxiv.org/abs/quant-ph/0611109

"Quantum entanglement communication" is one thing, FTL communication is another. Nobody has shown a way to get around the speed of light limit for communication, even with quantum trickery. I'd be thrilled if someone managed true FTL communication, but I'm not betting on it.

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Indeed. Although the particles correlate their behaviour instantaneously, observers can't use this instantaneous interaction to transmit useful information. IIRC, a distant observer will see essentially random behaviour in the incoming particle stream when viewed in isolation; the correlated behaviour will only become evident when the two observers exchange information about their particles with each other, which they must do at conventional, slower-than-light speed.

Grant Hutchison

The only way FTL communication would be possible would be if two particles remained entangled AFTER a measurement, which they do not.

The main issue with Quantum Entanglment communication is as has bee pointed out already, measuing the state destroyes the entanglement.

It's possible to have 100% Light Speed communication with Quantum Entanglment, instead of the effective 99.9% Light Speed of Radio's (eltectrons only travel at 99.9% speed of light through circutry).

To effect a FTL like Quantum Entanglment Communications, it would require eliminating the mesuring of states at the quantum level. Basically, you'd have to mass produce Entangled matter (such as Quartz Crystals) such that a varying electrical current that causes a oscilation in one, will have the oscilation mirrored in it's 'twin' casuing a varience in a steady electrical current on that side.

I think at current only Entangled Gasses have been made, and they have not lasted long (milliseconds) before disentangeling themselves, so it doesn't look good for producing solid matter that is entangled in the way needed.

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I'd really love to see FTL communication become a reality. The two main problems with QE is -as I gather from the posts above- is 1) that the entanglement is destroyed when you observe the particle (rendering it useless), and 2) even if you didhn't destroy the link by observing it, you would still need additional information about the other particle from the other caller on the quantum phone...

I was wondering if alien civs might use QE communication, and that SETI might never find any alien chatter in the ether because they use a more effective means of communication. (RF is limited to light speed, which makes it fairly ineffective for space faring races that have colonies lightyears apart).

But unless those quantum problems are solved, it remains wishful tinking.

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I read through Manchurian Taikonaut's links (on my ususal, superficial level) and noticed that the last one looked promising; from the abstract:
(my bolding)

Perhaps quantum telephones don't always need a classical channel after all. Or perhaps I just missed the point there.

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Nit: Electricity travels at around 2/3 c through circuitry (give or take, depending on the particulars of the circuit). Electrons, however, travel much, much slower.

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Only #1 matters. If measuring the particle didn't destroy entanglement, FTL communication would be very possible. Here's how it might work:

Imagine I have two electrons that are entangled, and I separate them a great distance. Now let's assume I want to send a message to my colleague. I tell my colleague to check the spin state of their electron every 1 second. Every second, I either flip the spin of my electron (by hitting it with another particle), or do nothing. If entanglement wasn't destroyed by this process, my partner could look at the state of their particle every second and record whether it flipped or not. This can be used to encode a message in binary, and voila, FTL communication! No additional information is required.

That's how I understand it. Particles are often naturally created in pairs, which are entangled by definition. There are particles that make up part of your body that have their entangled counterparts that are likely millions or billions of lightyears away. I thought it was Bell or Aspect or one of those guys who showed that some effect on one of those entangled particles will instantaneously affect the other one. But as you say, there is a random element that defeats the objective of FTL communication.

Well, after looking at what Wiki says about the matter (search on 'nonlocality') it is better described as follows:

Bell's theorem shows that Einstein's dream to complete quantum theory with new deterministic local theory with additional variables ("elements of reality") must fail. Such a theory must be non-local. Still this does not imply nonlocality of quantum mechanics, because this theory does not require, or imply, existence of an underlying deterministic structure. There is an interpretation of quantum mechanics which uses additional, experimentally inaccessible variables, that make it a deterministic theory. This is the Bohm interpretation. It is inherently nonlocal.

This is pretty deep stuff that seems to be just outside my "light" horizon. Of course, if the universe is non-local, it should be accessible. But....

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it's simple- they just sent the message "around" space and thru another dimension called "subspace".
isn't this pretty much how they also were able to fly across half the galaxy from one end of the federation to the other in a couple of weeks- well, except for poor Voyager- for some reason, that ship couldn't go that fast and needed over 70 years to fly across the same galaxy..

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So basically quantum pairs are just like ends of some kind of one-dimensional string. When you affect one end of the string (a particle), that change instantly ripples to the other end of the string (the particle's twin).

It's easier for me, at least, to conceptualize it that way.

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I am amazed at the lack of flexible thinking by persons steeped in the old "NO FTL COMMUNICATION" school of thought!

I always see the same old pat reply wirtten by rote-"No FTL communication because of random outcome of measurement, which is simply meaningless quantum noise."

I'm sure many of us as children manipulated the gain knob on a radio transmitter and sent "louder" and "softer" noise messages (much like the olf Morse Code) using white noise already available.

The fact is, the same can be done by heating a crystal lattice with entanlged electron pairs trapped in crystal lattice impurities. Turn up the temperature, and many more electrons spontaneously exit the crystal lattice impurity traps (no forced measurements, only increased probability of spontaneous escape from the crystal lattice traps). The crystalline ion impurity traps protect the electrons from environmental decoherence, so that they are "Trapped" in a metastable state once promoted from the ground state of the crystal lattice into the trap. Of course, entangled photons impinging on two such crystals can and do promote entangled electrons into these relatively decoherence free space traps.

Now move the two crystals apart from each other, set one or both under photo multiplier tubes, and begin to bring up the heat in one of the crystals. What happens? Lo and behold, the non-heated chip emits excess light due to electrons falling out of their traps at an accelerated rate due to the heat treatment of the other crystal. Tis occurs as a result of energy conservation laws when the electrons in the heated crystal traps escape and make spin transitions back down to the ground state of the crystal lattice. Of course, the entangled electrons in the other unheated chip must go thorough exactly opposite sign transitions and will also emit light.

This is most easily accomplished with commerically available Thermoluminescent Dosimetry chips (TLD's). Electronically produced x-ray phtons are entangled to a hihg degree, and easily promote electron pairs into rather long-lived metastable trapped states.

So, who says you can't communicate with (quantum) noise??? As long as controlled modulation of the noise is possible, there is no problem!

The greatest conceptual problem for most people is that they think quantum noise must be carefully directed via "qauntum channels" such as optic fibers over distance to a receiver. This is nonsense. Such concepts mix General Relativity and macroscopic space time constraints with quantum mechanis concepts.

Einstein's finest arguement is that the two theories AREN'T compatible. So why do we insist on trying to force the two incompatible concepts together when experimenting with entanglement?

One must simply accept that the two theories are good models in their correct contexts, but cannot be conceptually glued together in a hybrid theory. Attempting this will always casue contradictory results that tend to nullify each other.

Correct. The speed of information through coaxial cable is usually around 0.7c . Internally within the circuit, it risks being even slower.

Does this mean that you can transmit one bit with one pair of entangled particles? If so, then this would tell me all I need are LOTS of entangled particles and I could communicate back and forth for quite some time if I keep my bandwidth low.

[Please send my Nobel prize to P.O Box yada yada yada...]

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I think, the only really relevant question in FTL quantum telecommunication is: can the measurement of one of the entangled particles at one end be detected as an isolated event at the other end? Say, is it possible in any way that the reciever notices that the quantum state of the particle at the sender has been determined?

If yes, FTL communication should be possible. Either by the way discribed by vangent, or by using pairs of entangled particles, say A1, A2 (entangled) and B1, B2 (entangled). A1 and B1 stay at the reciever, while A2 and B2 go with the sender. Measuring both particles at the same time means 0, measuring only one of the two means 1. If it is possible for the reciever to determine if one (or both) of the particles has been measured by the sender, then this would mean FTL communication.

At least, this is my understanding of the situation.

Do we really know this to be the case though, or is this a simplification in the way quantum physics has been set up? Maybe changes in the state of the system only propogate at c. Otherwise, you'd have to have some sort of special reference frame for "instantaneous", as this doesn't have a frame-independent definition under SR.

Does the state change happen instantaneously in your frame, or the frame of the guy in the spacecraft travelling at .5c relative to you? Or the frame of the guy going .5c the other way? And if it happens instantaneously in one frame, does that imply anti-causal effects in another?

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This is exactly why, IMO, SETI is 'whistling in the dark' as it were. Advanced humans throughout the galaxy and beyond, in addition to having FTL travel, use FTL (nearly instantaneous) communications. Quantum entanglement, or spooky action at a distance, is one way. The other may be using gravitational potentials as transmittable 'information' where the receivers are able to read any code sent over that medium, instantaneously. Sending code over electromagnetic energy is very slow by comparison, which is okay locally but not good enough for interstellar space travel or communications. That's why SETI hears nothing... "Hello, hello?"

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