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What is the Modulus of an Eigenvalue?

  1. May 18, 2006 #1
    :confused: :confused: :confused:
     
  2. jcsd
  3. May 18, 2006 #2

    LeonhardEuler

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    The modulus of a real number is its absolute value. Since this is posted under quantum mechanics, I am assuming the the eigenvalue is real. In a more general case, though, the modulus of a complex number, a + bi, is [itex]\sqrt{a^2+b^2}[/itex].
     
  4. May 19, 2006 #3

    selfAdjoint

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    Yes, if you regard a complex number as a vector in the plane (Feynmann;s "little arrows") then its modulus is its length. This obviously agrees with LeonhardEuler's algebraic definition.
     
  5. May 19, 2006 #4
    I'd credit the arrows to Argand, not Feynman...
     
  6. May 19, 2006 #5

    selfAdjoint

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    Absolutely!:approve: I wasn't giving him credit for the idea, but in his little book QED he refers to the complex amplitudes on his paths as little arrows. I always thought that was both sharp and funny.
     
  7. May 25, 2006 #6
    If u r talking of QM. Then this question appears meaningless to me.
    In QM, every observable has got a hermitian operator representation. By the mathematics of hemitians we know they always have real eigenvalues.
    so a mod amounts to change of sign if the eigval is -ve
     
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