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

EPR paradox philoshophy is confusing me

  1. Nov 13, 2007 #1
    The philoshophy is confusing me. If i understand correctly, it comes down to the following:

    when a pion decays (which decays to an electron and positron), we can make a measurement of the spin of both resulting particles. If I measure the spin in the z-direction of the electron, I instantly know the spin in the z-direction of the positron. According to EPR, there are two possibilities:
    * measuring the spin on the electron the result instantly travels to the positron :
    ***spooky action at a distance -> impossible
    ***or the spin in this direction is an element of 'physical reality'

    However, the spin in 2 directions of a particle can't be simultaneously known (this would violate the heisenberg uncertainty principle), therefore quantum theory is incomplete.
    Is the line of thought correct?

    If we first measure the spin in the z-direction on 1 particle, then we can't say anything about the spin in the x-direction: it can still be two values. So in other words, the value the spin in the x-direction can have, depends on what we measure on the other particle. If we measure the x-direction of the electron, we KNOW what the spin in the x-direction of the positron will be. But if we measure the spin in the x-direction of the electron, we don't know what the spin in the z-direction will be.
    This is the paradox, right?
     
  2. jcsd
  3. Nov 18, 2007 #2
    The epr paradox and its philosophical implications are outlined rather well in this stanford article:

    http://plato.stanford.edu/entries/qt-epr

    I don't like the idea that measuring one particles state determines the other particles state- it suggests that the act of measuring participates in a particles quantum reality. The idea of action at a distance is more reasonable, but not if the act of measuring still determines the other state. The argument that I like best is that the state of each is determined at the origin, the creation of each, and that once we determine the state of the first particle that the other will follow as a necessity.

    The idea that quantum physics may be incomplete is valid, but in what respect is it incomplete since it is so successful? This type of result has led people to predict that a model may be found that one day explains these type of results. The problem that I have with quantum theory, epistomalogically speaking, is that it deals with the knowledge 'that occurs', rather than the knowledge 'how that occurs'. A structural model might answer how, but quantum theory is not a structural theory, it deals with the knowledge 'that occurs' only. The study of science in the quantum realm has taken on a twisted ontology, to such a degree, that it argues that their method becomes the reality of that subatomic realm. So what I may 'prefer' to see as a mathematical approximation of an electrons behaviour projected into this and that, they see as a description of not only fact but also the foundation of a quantum philosophy.
     
  4. Nov 18, 2007 #3
    This action at a distance article outlines the views that I discussed above.

    http://plato.stanford.edu/entries/qm-action-distance/

    I am confused about one thing. It is related that once the spin of one particle is determined, that the other should still have two possibilities- but only one shows...

    What if the spin of these particles is their internal spins? What if the internal spin of an electron is always the opposite of a positron? What if there is no other possibility? So no matter what we might think, determining the spin of one will always define the internal spin state of the other...

    I wonder if it is possible to have a beam of electrons, to take repeated measurements in the same manner of the EPR and to determine if all the results are the same. And then to do the same with a beam of positrons, and find that the opposite is always true. This is only a thought, and not very helpful. But it occurs to me that an electron might have an internal property, an internal spin that is not subject to any sort of uncertainty, and that this would show that quantum theory is incomplete and that there is the need for a model.

    For if an electron were to have say, a counterclockwise spin, then it would have a relativity of sorts with respect to the type of orbit it takes. And if the concept of an orbit is too classical for QT then how about approach, or interaction. For it could still approach, or interact with a proton in one of two directions. In other words, consider a proton in the distance, as an electron approaches it could moving to the left or the right.

    Consider the electron as a wheel that spins counterclockwise. If the electron were to orbit or pass a proton in a counterclockwise manner it would roll around the proton as it does so. If it orbits or passes in a clockwise direction it would essentially skid as it does so. If the proton has its own spin, say clockwise, then there could be a hidden variable, a condition created by the magnetic interaction of the two states. In which case, there could be two ground states for an electron, one shifted from the other.

    Just an idea.
     
  5. Nov 18, 2007 #4

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

  6. Nov 18, 2007 #5
    With respect to Bell's inequalities it is related that they break down. The difference between locality and nonlocality is the key construct. The idea of locality breaks down in the two slit experiment. Locality suggests a degree of separation between the two states of the EPR-so that action at a distance is eliminated. Whereas non locality is required to explain the effects of interference. There is a need for two slits to be open, and the argument is made that while something passes through one slit its probability requires the other slit to be open in order for its path to be determined.

    Quantum theory, in my estimation, was created to explain a specific phenomenon, and specifically the atomic spectra. The basic mechanism of atomic spectra involves the transition of electrons in an undisclosed manner and deals with electrons that are in bound states. Is it possible that there is a difference between that kind of environment and that of free electrons/ positrons in the EPR? In that respect, is it possible that quantum theory is discontinuous in some respect?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: EPR paradox philoshophy is confusing me
  1. Me. (Replies: 2)

  2. Is there a paradox? (Replies: 12)

  3. It's me (Replies: 4)

Loading...