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A Communication faster than light or where is my mistake?

  1. Apr 25, 2016 #1
    Hello, here is some reasoning how I got possibility to communicate faster than light.
    Likely somewhere are mistakes, but I can not find them by myself.

    Let's consider very simple setup with observers Alice, Bob and a source of entangled photons in-between of them like so:


    Let's say distance (Source..............................Bob) is twice as (Alice..........Source)

    Also let's say both observers have polarizers oriented equally, let's say vertically.

    Now let's begin the experiment. Source emits pairs of entangled photons.
    Left photon goes to Alice and right photon goes to Bob.
    Let's name them like photon (L) and photon (R).

    When photon (L) hits Alice's polarizer wave function collapse is happening.
    But photon (R) is still traveling. Let's say it is at point X during the collapse of mentioned wave function.


    Because of wave function collapse right photon (R) gets defined polarization.
    As I mentioned earlier both polarizers are oriented vertically,
    so the photon (R) at point X could get vertical or horizontal polarization
    (exactly the same polarization like photon (L) who just passed Alice's polarizer).

    So like a sequence both photons will act equally at both polarizers.

    Until now nothing strange was detected.
    But let's say distances are big enough.
    Now let's Alice rotates her polarizer by 45 degree.

    When next photon (L) will hit this polarizer opposite photon (R) also will get diagonal polarization at mentioned point X. This polarization will be diagonal like so “/” or like so “\”

    Now we see that some sort of information from Alice to point X travels instantly
    and only from point X to Bob information travels with velocity c.
    Ones again if Alice puts her polarizer vertically Bob will get 50% of vertically polarized
    photons and 50% horizontally polarized photons.
    But if Alice turns her polarizer by 45 degree Bob will get 50% of photons by this “/” diagonal polarization and 50% by this “\” diagonal polarization.

    The question is can Bob separate which photons are coming now,
    with polarization like so “|”and “--”
    or like so “/” and “\” ?

    If Bob can experimentally separate these 2 cases he can get information from Alice faster than light, because information about the angle of Alice's polarizer travels instantly from her to point X.
    What do you think?
  2. jcsd
  3. Apr 25, 2016 #2


    Staff: Mentor

    But he can't.
  4. Apr 26, 2016 #3
    Likely you are right, but still lets try to invent some measuring procedure to separate mentioned 2 cases.
    What if Bob obtain single photons from incoming beam and send them to amplifier.
    Let's say from 1 single photon he gets 1000 of them. All of them will have the same polarization.

    Now Bob splits these photons into 10 (or more) groups and each group of photons sends to a separate polarizer. Let each polarizer has different angle of polarization.

    From the total outcome how all these 1000 photons have passed all polarizers could be possible to find out polarization of the initial photon Bob was measured.

    Am I right or maybe here are some more mistakes?
  5. Apr 26, 2016 #4


    Staff: Mentor

    It doesn't work this way. Spacelike separated operators commute, so there is simply no possible way that anything done on one photon will affect the outcome of a measurement of another photon faster than light. It doesn't matter if you use an amplifier a beam splitter or whatever.

    Personal speculation is not permitted. Thread closed.
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