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Thread: FTL comunicaton

  1. #1
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    FTL comunicaton

    After lots of thinking about quantum teleportation, i got this idea:
    not sure if it can work, so I will be glad to discuss it.
    I suppose that: it is impossible to send or receive half or less than one photon(however seems it is possible to reflect part of photon)

    ------ this way probably will never work so do not discuss it anymore---------
    This can be used for FTL comunication, because you cant receive half of photon.
    We can use this schematic:
    receiver1 <--500m----- transmitter ---------800m-----------> receiver2
    transmitter sends one photon at fixed intervals, either receiver can receive or ignore it if receiver 1 will take it then receiver2 wont get it because receiver1 take it first. so if you receive photon you will send 0 or if you ignore it you send 1.
    (This is little related to quantum teleportation experiments, but instead of receiving, photon go through 2 slits, then create interfecence patern with itself.)
    --------------------------------------------------------------
    here is new way http://www.bautforum.com/showpost.ph...7&postcount=16

    the point is that singe photon trawels 2 patches at once. So one path can be very long and other can be very short. controling long path you can controll interference pattern. and transmit data that way.
    Last edited by Digix; 2006-May-07 at 01:05 PM.

  2. #2
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    If the photon has 2 possible paths, either towards receiver 1 or receiver 2, then you have 2 possibilities.

    1) You leave receiver 1 there to catch a photon, both receivers have a 50% chance of catching it.

    2) You move receiver 1 so it doesn't catch it, there's a 50% chance that the photon goes undetected past where receiver 1 was, and 50% it goes to receiver 2.

    In either case, receiver 2 gets half of the photons and can't tell if receiver 1 caught or ignored the rest. How do you use that for communications?

  3. #3
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    I think he's talking about entangled pairs... right?

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    Quote Originally Posted by Digix
    After lots of thinking about quantum teleportation, i got this idea:
    not sure if it can work, so I will be glad to discuss it.

    I suppose that: it is impossible to send or receive half or less than one photon(however seems it is possible to reflect part of photon)

    This can be used for FTL comunication, because you cant receive half of photon.
    We can use this schematic:
    receiver1 <--500m----- transmitter ---------800m-----------> receiver2
    transmitter sends one photon at fixed intervals, either receiver can receive or ignore it if receiver 1 will take it then receiver2 wont get it because receiver1 take it first. so if you receive photon you will send 0 or if you ignore it you send 1.
    (This is little related to quantum teleportation experiments, but instead of receiving, photon go through 2 slits, then create interfecence patern with itself.)
    The receivers still need to communicate to each other that they are either ignoring the photon or not. The communication can't beat the photon already on its way to each receiver, therefore no FTL communication is possible with this scheme.

  5. #5
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    I read someting once about using a combination of entagled matter and the cashmir effect to affect FTL communications.I won't go into details yet, until I can find the source again.

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    Quote Originally Posted by dgavin
    I read someting once about using a combination of entagled matter and the cashmir effect to affect FTL communications.I won't go into details yet, until I can find the source again.
    I don't see how the casimir effect would play any part...

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    Well haven't found that source yet.

    But basically it involved two sets of entangled matter plates such that each pair is entangled with the the other. One plate in transmiting set is heated and cooled electrially, causing it to warp towards or away from it's partner. This would theoretically be reflected in the entangled set some x LY distant. On the reciving side you measure not the quantum state (hiezenberg uncertainy rules there) bet the variations in the casmir effect (i assume ZPE?) from the plates expanding and contracting.

    I think the main issue (road block) here is something about entangled matter having been made so far, only lasting a few milliseconds.

  8. #8
    FTL would indicate speed (distance/time) where as quantum teleportation seems to negate those altogether.

    I'm just trying to clarify terms here as my understanding of the whole subject is still at the "pick up rock. let go. rock falls - gravity still works" stage.

  9. #9
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    Cool causality

    Faster than light communication always brings in causality issues.. .kind of like Paul Newman, and 'the wire' in The Sting, with his victim Lonergan. Don't think that's ever going to happen in the real world, though it was funny in the movie.

  10. #10
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    I actualy talk about using single photon, entalged pairs do nothing usefull.

    Quote Originally Posted by phunk
    If the photon has 2 possible paths, either towards receiver 1 or receiver 2, then you have 2 possibilities.
    1) You leave receiver 1 there to catch a photon, both receivers have a 50% chance of catching it.
    2) You move receiver 1 so it doesn't catch it, there's a 50% chance that the photon goes undetected past where receiver 1 was, and 50% it goes to receiver 2.
    In either case, receiver 2 gets half of the photons and can't tell if receiver 1 caught or ignored the rest. How do you use that for communications?
    I refer to double slit experiment: http://en.wikipedia.org/wiki/Double-slit_experiment
    one photon go through both slits at once, or else there will be no interference. However seems there is uncertainity which point of screen will receive photon. another experiment with quantum computing
    http://www.cs.caltech.edu/~westside/quantum-intro.html
    it says that photon trawels both paths at once, if so, we somehow sould be able to choose at which path take it.
    Unfortunately I cant find any information what happens if v and h path have different length.

    In either way photon interference with itself requires faster than light speed, or else there is no way to go through 2 slits at once and create interference.
    because one "part" of photon must be faster than other, or if the speed will be exactly equal, we will see no interference at all (path length is different for each slit.)
    example of interference pattern http://www.colorado.edu/physics/2000...twoslitsa.html

    Quote Originally Posted by trinitree88
    Faster than light communication always brings in causality issues.
    That is not true, it is neither proved experimentaly, neither have any theoretical reasons. All is based on mathematical infinity divide by infinity.
    Also any thoery does not forbid you to send information faster than light. unfortunately now there is no tested way to send information without attaching it to energy.

  11. #11
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    I have to agree with DigiX on the Causality Violation.

    Vilolating Causality means that the Effect happens before the Cause, without relation to any frame of reference or to any stationarry or moving observer. (tacheons if found would be an example of Causality Violation, as they would travel backwards through time, while going forwards through space)

    Causality has nothing to do with observer A seeing an Effect before Observer B, Or Observer A moving fast enough to a point farther away, and then sitting there to watch the light echo of his leaving reach him at his new location.

    Quantum Entaglement action at a distance doesn's exibt causality behavior, as if matter was being accelerated past FTL. It's a case where the cause and then effect are Linked and close to Simultaneous. If you try to measure the Effect, you are performing an action (Cause), which disturbs the original cause/effect you try to measure (hiesenberg uncertainty).

    However side effects unrelated to the Entagled cause/effect can be directly measured without changing the state of the entangelment.

    Persay if you Quantum Teleport matter to a receiver at 50 LY didstance, which immediately Teleports the Same matter back to origionator, it will arrive later then when it left, later being the time it took to recive then retransmit the matter. Causality is perfectly conserved.

    Now if you pushed the same matter to FTL speed's using acceleation, and then sent it back, it would viloate causality as it would arrive before it left...

    But until we can make stable entagled matter (which is an unknown if this is possible) there would be no method to mesure side effects of the entaglement effects, without disturbing the origional state changes.

  12. #12
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    Quote Originally Posted by Digix
    In either way photon interference with itself requires faster than light speed, or else there is no way to go through 2 slits at once and create interference.
    because one "part" of photon must be faster than other, or if the speed will be exactly equal, we will see no interference at all (path length is different for each slit.)
    example of interference pattern http://www.colorado.edu/physics/2000...twoslitsa.html

    Wrong. You are misinterpreting the experiment. The purpose of the double-slit experiment is to demonstrate the wave-like behavior of photons and matter at that scale. The same banded pattern occurs when electrons are used instead of light. In fact it is the wave-like propagation of the wave fucntion that creates the banded pattern on the screen; no FTL required.

    it says that photon trawels both paths at once, if so, we somehow sould be able to choose at which path take it.

    Wrong again. That's the whole point of quantum mechanics is the uncertainty that you have to deal with in terms of position and veloicty. The only way to force a path is to close one of the slots. In that case, you've now collapsed the wavefunction into a point-like particle.

  13. #13
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    Quote Originally Posted by Omicron Persei 8
    Wrong. You are misinterpreting the experiment. The purpose of the double-slit experiment is to demonstrate the wave-like behavior of photons and matter at that scale. The same banded pattern occurs when electrons are used instead of light. In fact it is the wave-like propagation of the wave fucntion that creates the banded pattern on the screen; no FTL required.

    it says that photon trawels both paths at once, if so, we somehow sould be able to choose at which path take it.

    Wrong again. That's the whole point of quantum mechanics is the uncertainty that you have to deal with in terms of position and veloicty. The only way to force a path is to close one of the slots. In that case, you've now collapsed the wavefunction into a point-like particle.
    Of course purpose of experiment was another than FTL demostration, but the point is that photon must trawel different distances in case it chooses different slits.

    Uncertanity is not explanation, it is just some kind of observed fact. I prefer theory of hidden variables instead.

    Quote Originally Posted by Omicron Persei 8
    The only way to force a path is to close one of the slots.
    that is quite enough for FTL comunication, if you can force particle patch.

  14. #14
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    Quote Originally Posted by Digix
    Of course purpose of experiment was another than FTL demostration, but the point is that photon must trawel different distances in case it chooses different slits.

    Uncertanity is not explanation, it is just some kind of observed fact. I prefer theory of hidden variables instead.


    that is quite enough for FTL comunication, if you can force particle patch.
    No, you have to remember that, even as a wave, its velocity can only travel at the speed of light.

    It's based more on the probability of where a particle lands on a detector. See linky

    Question. Do you have the math to back up your claim?

  15. #15
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    Quote Originally Posted by Omicron Persei 8
    No, you have to remember that, even as a wave, its velocity can only travel at the speed of light.

    It's based more on the probability of where a particle lands on a detector. See linky

    Question. Do you have the math to back up your claim?
    There is no math to prove it, but geometry should work. I will try to make picture later, the point is that single photon must trawel diferent path length to create interference. Imagine that we put slits far from each other and screen relatively near to them. unfortunately I dont know any experiments to prove FTL posibility directly.

  16. #16
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    Here is picture how it would look like, if we assume that light do not bend in the vaccum you can see that path l1 is shorter than l2 when interferense pattern is created on screen, if we assume that photon took the short patch then how it can interfere with itself when its other "part" will reach screen some later.

    If we use multiple photons there is no such problem, but in case of one photon there is. My assuption is not based on wave propereties, they are based on quantization and interferense with itself.
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  17. #17
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    I think you're misunderstanding something here. The whole point of the experiment is show that the only way this phenomenon can happen is when photons (many or just one) can also be wavelike and subject to diffraction through the slots.

    All the diffraction info you'll ever need

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    I do not care what was intention of experiment, I am jut using its results here.
    On your link it explains interference, but I care about single photon interferense with itself here, and that is the main point.

  19. #19
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    Quote Originally Posted by Digix
    I do not care what was intention of experiment, I am jut using its results here.
    On your link it explains interference, but I care about single photon interferense with itself here, and that is the main point.
    You mean this?

  20. #20
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    That's right. experiment had diffrent purpose, but can be used here too.
    here they do not mesure time which is required for photon to reach detector.
    so my point was: how photon can interfere with itself if it needs different time to reach the screen in case it chooses diffrent patch.

  21. #21
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    I can actually explain that.

    Photons exist in a frame of reference where time is always 0 (does not exist) for them.

    IE Photon leaves source and arrives at slot 1 or slot 2. From our point of view, slot two is offset and it take the photon longer to get there. From the Photons point of view, there is no difference between the time it gets to slot 1 and the time it gets to slot 2. No time has passed for it. For the photon, both journeys even though one was sligtly longer, were instantatious.

    There for there is nothing to prevent it from interfering with itself, where one path in longer, in a frame where there is no movement though time.

    *edit* It was this that led to the theory and discovery of Quantum Entanglement. Single phontons in some rare situations exibit Spooky Action at a distance behavior. This led to the suppostion that a photon was infact two (still unknow what kind) particles somehow entangled.

  22. #22
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    Quote Originally Posted by dgavin
    I can actually explain that.

    Photons exist in a frame of reference where time is always 0 (does not exist) for them.

    IE Photon leaves source and arrives at slot 1 or slot 2. From our point of view, slot two is offset and it take the photon longer to get there. From the Photons point of view, there is no difference between the time it gets to slot 1 and the time it gets to slot 2. No time has passed for it. For the photon, both journeys even though one was sligtly longer, were instantatious.

    There for there is nothing to prevent it from interfering with itself, where one path in longer, in a frame where there is no movement though time.

    *edit* It was this that led to the theory and discovery of Quantum Entanglement. Single phontons in some rare situations exibit Spooky Action at a distance behavior. This led to the suppostion that a photon was infact two (still unknow what kind) particles somehow entangled.

    Quite interesting, so you say that it will work?
    since that "spooky action" is faster than light.
    I can make path L1 few cm and path L2 few km or more.
    then ontroling slit on path L2 I will controll interference.
    Of course there is question left. How long it will take for light to travel from source to detector? Will it be random time for either path, or it will be average, or maximal time?

  23. #23
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    Yes techically an offset double slit experiment should work, I cannot site a specific reference where it has been done however.

    I do know the the praticles within a photon are probably entangled, and it possible to make photon pairs that are entangled, and even some gasses seperated by a few feet to be entangled (for around a millisecond).

    But at this level, if you try to measure whats happening you typically break the entanglement or only measure one probaility of many (heizenberg uncertainty).

    As to the spooky action at a distance, the light to use still moves at a fixed rate, there for we couldn't use light (even through a spooky action proccess) to send information fater then light. The light to us still travels at is fixed rate through time.

    Got to get to work, will post more later

  24. #24
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    Entalgement is quite useless for comunication, maibe it can be used for ecryption, but will not do much either. I think entalgement is as syncronizing some clocks, if you read one you destroy it, but you know what another was showing at that time.

    Here I suggest use single photon not entalged pair. Tecnicaly this kind of comunication does not violate speed of light, since it does not transfer energy.
    Also it may be possible to use RF signal instead of photons.

  25. #25
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    Well the 'spooky action at a distance' refers to quantum entangelment. Single photons in a double slit experiment can exhibit this kind of behavior.

    However even though the interference is visable to us (because that happened in the lights frame of referece where time = 0) If you could see each path of the photon without effecting it, one would talke longer to reach the detector then other in our frame of reference.

    This is why Einstien called it 'Spooky'.

    I don't see how this could facilitate FTL communication though as it doesn't seem likely a single photon could exist at earth, and say at mars at the same time in our reference frame. Yes you could encode information into an interference pattern, but that would travel with(as) the photon itself.

    I've simplified SR/GR into something a bit more easy to understand for myself wich might help you with this.

    Space/Time is not understood as to what it really is or how the Speed of Light is defined by it.

    Space/Time imposes certain restrictions, depending on Mass.

    If Rest Mass > 0 then a particle requires infinite energy(an imposibility) to reach light speed. It moves forward though space and time.

    If Rest Mass = 0 then a particle always moves at the speed of light, adding energy does not accelerate or otherwise change it's speed, but effects some other aspect, such as frequency. It moves forward through space, but not through time. Time is Zero relative to itself for any particle moving at the speed of light.

    If Rest Mass < 0 then a particle requires infinite energy to slow down to the speed of light. It moves forward through space faster then light, but backwards through time. Time is always negative and works inversely of a particle that has positive mass.

    The above is basically an english explaination of how SR/GR applies to us with reguars to particles. Waves can be subsituted for particles in my explaination.

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    Quote Originally Posted by dgavin
    I don't see how this could facilitate FTL communication though as it doesn't seem likely a single photon could exist at earth, and say at mars at the same time in our reference frame. Yes you could encode information into an interference pattern, but that would travel with(as) the photon itself.
    I suggest use very different way, plave both detector and transmitter in the earth and, and one of slits in the mars.
    noone in the mars will ever see any photons, but they controll interference pattern in the earth.
    actualy this way is used in quantum computers, because if you use information medium with linited speed you cant instantly solve problem.

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    There has been experiments done where examining the wave of a particle as it tunnelled through a short distance. They showed that parts of the wave actually tunnelled at something like 20c BUT never was enough of the wave tunneled faster then c so that you could extract any information about the state of the particle.

    So it seems that even spooky action at a distance is not capable of transmitting even quantum information faster than c.

    This page has a list of papers on the subject:-
    http://www.aei.mpg.de/~mpoessel/Phys...nelingftl.html

    or just google quantum tunneling faster light

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    Forget what you think you know of the double-slit experiment
    http://axion.physics.ubc.ca/rebel.html

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    Forget what you think you know of the double-slit experiment
    http://axion.physics.ubc.ca/rebel.html
    Firstcontact,

    Correct me if I am wrong but this reference is confirming the standard interpretation of the two slit experiment and refuting the new interpretation put forward by Afshar.
    the gain in inference from the detector to "whcih path" is exactly balanced by loss of certainty about the interference pattern ( paths 3 or 4), which is also in accordance with complentarity. The more you can infer about "which way" the less you know about the interference.
    I fail to see how you draw the conclusion to forget the standard interpretation. Please explain.

  30. #30
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    Quote Originally Posted by loglo
    There has been experiments done where examining the wave of a particle as it tunnelled through a short distance. They showed that parts of the wave actually tunnelled at something like 20c BUT never was enough of the wave tunneled faster then c so that you could extract any information about the state of the particle.
    I dont see how this double spit experiment is realted to tunneling.

    Here I talk about interferense of single photon with itself.
    One "half" of photon will trawel 10cm, while other "half" will trawel few m or km until ir reaches same screen, and interfere. If photon speed are equal, then if it choses short path it will be received much sooner than if it chooses long path. So how they can interfere if second half will arrive after few miliseconds when first half already do not exist.
    Also in this way we can easily detect which path photon traweled, what contradicts with quantum uncertainity.

    As I know no experiment was done to measure timing. Probably that should be quite easy, but still somehow hard to do at home, since I need very short pusle laser.

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