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Systems with global phase invariance, 3D string?

  1. Apr 28, 2009 #1
    From:

    http://en.wikipedia.org/wiki/Quantum_mechanics#Mathematical_formulation

    ...
    In the mathematically rigorous formulation of quantum mechanics, developed by Paul Dirac[7] and John von Neumann[8], the possible states of a quantum mechanical system are represented by unit vectors (called "state vectors") residing in a complex separable Hilbert space (variously called the "state space" or the "associated Hilbert space" of the system) well defined up to a complex number of norm 1 (the phase factor).
    ...

    Let a three dimensional analog of a one dimensional string completely occupy the space S^3. Movement only occurs in some tangential space, let this space be S^1. This system has a type of global phase invariance, an equal global change of the coordinate in the space S^1. Any point P in S^3 labels a point of our "3D string". An additional coordinate gives the position of point P in our space S^1. If all points in S^3 have the same coordinate in S^1 then the system will be at rest and will be in a minimum energy configuration. The state of this system does not change with a global coordinate transformation.

    Now give the 3D string some energy and then freeze time. The physics is contained in the 3 dimensional surface that occupies the space S^3 U S^1, the union of S^3 and S^1. Again a global phase change does not change the physics.

    Thanks for any thoughts.
     
  2. jcsd
  3. Apr 28, 2009 #2
    andy everett wrote:

    > From:
    >
    > http://en.wikipedia.org/wiki/Quantum_mechanics#Mathematical_formulation
    >
    >
    > ...
    > In the mathematically rigorous formulation of quantum mechanics,
    > developed by Paul Dirac[7] and John von Neumann[8], the possible states
    > of a quantum mechanical system are represented by unit vectors (called
    > "state vectors") residing in a complex separable Hilbert space
    > (variously called the "state space" or the "associated Hilbert space" of
    > the system) well defined up to a complex number of norm 1 (the phase
    > factor).
    > ...
    >
    > Let a three dimensional analog of a one dimensional string completely
    > occupy the space S^3. Movement only occurs in some tangential space, let
    > this space be S^1. This system has a type of global phase invariance, an
    > equal global change of the coordinate in the space S^1. Any point P in
    > S^3 labels a point of our "3D string". An additional coordinate gives
    > the position of point P in our space S^1.

    We need another "coordinate", time.


    > If all points in S^3 have the
    > same coordinate in S^1

    for all time

    > then the system will be at rest and will be in a
    > minimum energy configuration. The state of this system does not change
    > with a global coordinate transformation

    of the coordinate in S^1.

    .
    >
    > Now give the 3D string some energy and then freeze time.

    We imagine the 3D string will evolve with time. For each point on S^1 we must have a tangential space (R^1 works) to plot the velocity of our point P in our space S^1.


    > The physics is
    > contained in the 3 dimensional surface that occupies the space S^3 U
    > S^1, the union of S^3 and S^1.

    Not right.


    The physics is contained in 4 dimensional surface in the space:

    S^3 U S^1 U R^1 the union of the spaces S^3, S^1, and R^1.

    > Again a global phase change

    of the coordinate of S^1

    > does not
    > change the physics.
    >
    > Thanks for any thoughts.

    I hope I got it right this time, thanks for any thoughts.
     
  4. Apr 29, 2009 #3
    andy everett wrote:
    > andy everett wrote:
    >
    ...
    >
    > > The physics is contained in the 3 dimensional surface that occupies
    > the space S3 U S1, the union of S3 and S1.
    >
    >
    > Not right.
    >
    >
    > The physics is contained in 4 dimensional surface in the space:
    >
    > S3 U S1 U R1 the union of the spaces S3, S1, and R1. ...

    Still not right.


    Our 3D string starts out as a 3D solid in S^3. Movement occurs in the space S^1. We add the space of the real number line, R^1, at each point on S^1 so we can "plot" the velocity of a point in S^1. The 3D string moves in the space S^3 U S^1 U R^1. Just as a 2 dimensional sheet of paper stays 2 dimensional as we move it about in 3 dimensions our 3D string also stays 3 dimensional as it moves in S^3 U S^1 U R^1. It may and will stretch. So the above quote should read:

    "The physics is contained in the 3 dimensional surface that occupies the space S^3 U S^1 R^1, the union of S^3, S^1, and R^1."

    The surface may get "twisted" as a function of space coordinates S^3, increasing potential energy of the 3D string. Each small volume of the 3D string may have some velocity in the space S^1 resulting in kinetic energy of the 3D string. So we have a simple dynamic system where physics does not change under a global rotation of a coordinate. I'm sure there are many other such realizations.

    Thank you for any thoughts.
     
  5. Apr 29, 2009 #4
    I wrote:

    "... So we have a simple dynamic system where physics does not change under a global rotation of a coordinate. ..."

    Because of this do we get some conserved quantity?

    Thanks for any thoughts.
     
  6. Apr 29, 2009 #5
    Would that be conservation of momentum in the space S^1?
     
  7. Apr 29, 2009 #6
    Can we produce dipole like radiation with our 3D string? I think so.

    Grab two points, P1 and P2, of our 3D string that are "near" each other. Move each point such that their coordinates in S^1 vary with time as:

    P1 = d*sin(w*t)
    P2 = -d*sin(w*t)

    where d is much smaller than the radius r of S^1. For points of our 3D string an equal distance from P1 and P2 the forces will cancel and for those points the coordinate of S^1 will not change with time. But for all other points the forces will not cancel and we will have outward going waves.

    Thanks for any thoughts.
     
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