Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Relativity Paradox Question

  1. Jun 11, 2004 #1
    I was reading Brian Greene's the elegant universe when I came across the section talking about how two people Gracie and George are traveling past each other in empty space. To each other they are stationary and the other is moving, therefore to each other the other's clock is slower. Greene discusses setting the clock to 12:00 and passing each other and how in order to check clocks later even by cellualr communication the max speed is that of light so the time it would take to contact the other to ask the the time on their watch would more than compensate for the slowness of the clock. In fact i believe he said that if there was something that was instantanous it would mean the fall of the theory. Here is my question. As far as not being able to communicate instantly there may infact be a way I thought of from my physics class. If you seperate the electrons in an electron pair no matter how far the distance the pair still "sees" itself as being connect and when one is fliped the other instantly does. I believe the space program is working on this idea to create a phone that would be used on longer than mars missions. So my question is what would happen if they were called each other using a electron pair phone?
     
  2. jcsd
  3. Jun 11, 2004 #2

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    Reduce it the problem:

    When (the component of spin along some axis of) the 'transmitter' electron is measured you will obtain randomly either a value of +0.5 or -0.5, if the value is +0.5 then the 'receiver' electron will have a value of -0.5 and vice versa. Before this time neither electron has a definite value.

    How then can this used to transmit information? If the receiver measures his electron, he gets exactly the same results if the tranmitter has measured his electrons or not (even though in the first instance it means that his elctron already has a definite value and in the second instnace it doesn't), so there's no way of sending any useful information via this method.
     
  4. Jun 11, 2004 #3
    way to communicate

    It has been suggested and is actually possible right now to control the fliping of electrons (although right now it is done in huge facilities) thereby if you can create a code with some sort of 1 and 0... say something similar to binary there is way to communicate messages
     
  5. Jun 11, 2004 #4

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    I think you may be muddled up because it goes against the fundmental postulates of quantum physics to control which eigenstate the electrons will collapse into 9though you exert a measure of control on the proabilty, but that in no way makes the entanglend electron phone possible)
     
  6. Jun 11, 2004 #5
    hmm, I was told in class that they are already able to control the the electron pair and flip it when they want to and watch it to see where it is at. The problem like I said earlier was the size of the device, my problem like what you infered as this presents problems for SR like when when two people moving call each other on one of these things to check watches it destroys sr properties.
     
  7. Jun 11, 2004 #6

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    I really can't see how you can control the collapse of the wavefunction so that you can 'decide' which eigenstate you get. If this were the case it would falsify quantum physics. You can exert control over the expected value, etc, but you just can't be assured of getting the same value everytime.
     
  8. Jun 11, 2004 #7
    -I more see a problem in SR, anyway I am looking for a site where i can show you some of the research
     
  9. Jun 11, 2004 #8

    selfAdjoint

    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed


    You can set up the experimental conditions so the AVAILABLE set of eigenfunctions is down to one or two, and then set up interferences that eliminate one of the possibilities. Look up "quantum eraser" or read the book Schroedinger's Kittens by John Gribbin. This does not violate the canons of QM but rather cleverly manipulates them.
     
  10. Jun 11, 2004 #9
    So if it IS possible to set up what would happen if the two talked wouldn't this voilate the laws of relativity indicated that there would be one true answer, and that they both couldn't see the others clock running slower
     
  11. Jun 12, 2004 #10

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    No it's still impossible to comunictae solely using entanglemnt, the point is if you have a wavefunction that will give a ceratin set of eigenfunctions after collaps you cannot specifically choose which it will collapse into, though as self-adjoint points out you can eliminate some of the eigenfunctions avidable to obtain the desired eigenvalue.

    The quantum eraser involves a measuremnt on one pair of entangled photon which allows you to detrimine the stae of the phton without measuring it. If we apply that to our experimnet we find that in order for this to be useful the two people on the electron telephones have to speak to each other via anther method to share the results of their experiments.
     
  12. Jun 12, 2004 #11
    I am not talking bout collapsing anyting, merely being able to "flip" an electron, keep in mind I have only taken one year of physics, however when my physics teacher comes back from his trip I will ask him to clarify what he was talking about. He was telling us that this is a reality and they already have the equipment to do it, they just need to make is smaller and create the language.
     
  13. Jun 12, 2004 #12
    add on

    Additionaly wouldn't it be true if anything was in the same quantumstate it would flip instantly if its brother particle was fliped.
     
  14. Jun 12, 2004 #13

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    Yep you can 'flip' the electron but then the values are either (0.5,0.5) or (-0.5,-0.5) as opposed to (0.5,-0.5), (-0.5,0.5)
     
  15. Jun 12, 2004 #14
    yes thats the whole point I believe you are able to see if its .5 .5 or -.5 or -.5 and becasue of this u are able to make a code have .5 .5 be one or -.5 -.5 be zero then you could have binary system
     
  16. Jun 12, 2004 #15
    I think through more thought that this is whole point we are looking for toe, my thought experiment represents the conflict between QM and GR without any math :)
     
  17. Jun 13, 2004 #16

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    No as it is impossible to use this method to communicate, it doesn't represnt a paradox with rleativity (and general relativity has been completly ignored here via the tacit assumptions)
     
  18. Jun 13, 2004 #17
    How is it impossible.... if you can control the state of the electrons in the same quantum state.... which you can.... and you can check to see if they are both possitive or both negitive .... which you can.... then you can make a device to communicate. Hell you could use a morse code system if you wanted to. It will be a long time before you could make any sort of voice system off of this if it would be even possible... many theorize it can be done... but for now the binary or morse code system is in the not to distant future.

    So if we have the phone....
    And we have two people moving past each other
    They both see the others clock running slower because of relativity
    They are allowed to compre clocks because of the phone which works because of as self adjoint pointed out clever manipulation of Quantum Mechanics...

    Therefore they both can't be right
    IE
    GR vs QM
    IE
    Conflict 3
    IE
    why we need TOE
    IE
    I like saying IE
     
  19. Jun 13, 2004 #18
    GR is involved because GR states that no inflence can travel faster than c, which in this case it can.
     
  20. Jun 13, 2004 #19

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    You cannot choose into which state the elctrons will collapse though which is the fundamental problem, the quantum earser allows you to choose, whether or not you have a superpostion of one state or two states (for example), but it doesn't allow you to choose the one state.

    Thios doesn't demonstrate the conflict with genral relatvity as we only need to consider special relatvity here and there is no irresovable conflict between quanum mechanics and special relativty EVEN though special relatvity tells us that information can't travel faster than c.
     
  21. Jun 13, 2004 #20
    GR states no influence can travel faster than c which would be what the QM phone would do. I am still trying to find this damn article... I will though :)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Relativity Paradox Question
  1. Relativity question (Replies: 9)

Loading...