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

Emergent coordinate systems in quantum physics

  1. May 26, 2014 #1
    Do unobserved particles exchange information with other particles? If not then they are not only unobserved but also un-observing, which would seem to mean that they not only do not have a well defined position but that the very concept of position does not exist for them, nor does distance or speed or direction or any other property that involves those listed. Unobserved particles have no reference frame until they interact with other systems. This is my interpretation of so called weirdness. I would like comments and to know if this is at odds with accepted theory.
  2. jcsd
  3. May 26, 2014 #2


    User Avatar
    Science Advisor

    What do you think happens in scattering experiments? We prepare particles in an initial state, arrange for them to collide, and observe the output particles. We don't observe the detailed interaction by which the initial particles transform into the output particles.

    So (of course) interactions don't somehow "switch off" when we're not directly observing particles.
  4. May 27, 2014 #3
    My post was an attempt to explain how a particle can be in more than one location at a time and the" spooky action at a distance" that Einstein objected to. If you imagine that you are the particle what would see, if you cannot see the rest of the universe then the concept of location does not apply to you.
  5. May 27, 2014 #4


    User Avatar
    Science Advisor

    If we don't observe a particle's spin, that does not mean that the particle has "more than one spin at the same time". It does not mean that the particle does not have a spin. And it does not mean that the concept of spin does not apply to this particle. It simply means that the particle is in a superposition of states with different spin. You're reading entirely too much into this.
  6. May 27, 2014 #5


    Staff: Mentor

    Particles are not in more that one location at a time - what they are doing when not observed is anyone's guess although various interpretations have their own take. 'Spooky action at a distance' depends entirely on the interpretation you have of a quantum state - in some it has that issue - in others it doesn't.

  7. May 28, 2014 #6
    Bill: I disagree imagine that you are the particle and you look around you, if you are not receiving information from other particles what test could you do to determine your position or speed. Position is defined by your relation to other objects that you see. Einsteins' "do you really believe the moon is not there when you're not looking at it", should have been how do you define there .
  8. May 28, 2014 #7


    User Avatar
    Science Advisor

    That's fine. I wasn't expecting to convince you anyway. :smile:

    This is the familiar cat paradox, from the point of view of the cat, who is in a superposition of states. Feel free to interpret a superposition any way you like, but don't expect that a classical interpretation will be sufficient.

    For a system which is not interacting with the rest of the universe, its current state is determined by its initial conditions and its subsequent evolution according to the Schrodinger Equation.
  9. May 29, 2014 #8
    Bill, I am not quite getting how all these sentences can be true at the same time. If it in a superposition does that not mean the spin is indeteminate?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook