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Indivisible units of time and the quantum eraser experiment

  1. Jun 25, 2015 #1
    If we take an indivisible unit of time (a Planck time perhaps), could the possible retro-causality hinted at in the Quantum Eraser Experiment be a process where the retro-causality goes back along the same plank unit rather than back in time per se

    Metaphor - I don't travel to a different train carriage, just the back of the same carriage.
  2. jcsd
  3. Jun 25, 2015 #2
    There is no indications of indivisible units of time. Time is the same on micro scales as it is in macro scales, it doesn't even have the same rate for different velocities or locations in a gravity well, meaning one second for one location could be two seconds for a different location but the physics remains the same locally. The quantum eraser experiments have been done with not nearly enough time for a delayed choice to affect what occurred at a fork "a long time ago" by photon propagation time scales.

    In a train analogy, what happens is when the engine at the front of the train has a choice to go left or right and someone at the back of the train says "I don't know which way we are going". As soon as the engineer determines which track to take, the person at the back of the train "instantly" knows a choice has been made, long before any information could reach them.
  4. Jun 25, 2015 #3

    How could we divide light travelling a Planck length in a vacuum?
  5. Jun 25, 2015 #4
    Into as many "slices" of time that makes sense. If it were a very high energy gamma photon, it could have 1000's of waves in that distance.
  6. Jun 25, 2015 #5


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    Staff: Mentor

    There's no particular reason to think that the Planck time is indivisible... but even if it were, how does it compare with the time differences involved in the delayed choice experiment?

    It would be a good exercise to calculate the energy of such a photon, see how it compares against the energy of various other interesting phenomena.
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