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Relativistic vs. non-relativistic quantum mechanics

  1. Mar 27, 2013 #1
    Would one consequently use relativistic QM or in some cases use the non relativistic postulates when dealing with a problem in the same that classical physics are used frequently when one deals with objects travelling at speeds much lower then the speed of ligth??
     
  2. jcsd
  3. Mar 27, 2013 #2
    Than* light*
    My iPad's autocorrect, one might question whether the name is fitting, is playing around.
     
  4. Mar 27, 2013 #3
    One fairly uses non-rel. QM when dealing with low energy systems. The only systematic and meaningful way of using relativistic QM is through quantum field theory, when one has to deal with the possible creation/annihilation of particle species.
     
  5. Mar 27, 2013 #4
    But is a general inadequacy in the theory to blame for the limited use or does it just speak to the practical nature of physicsist?

    And wouldn't one risk missing important points if one's system evaluation is non relativistic?
     
  6. Mar 27, 2013 #5

    George Jones

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    If you drop your keys, do you use general relativity to calculate how long it takes your keys to hit the ground?
     
  7. Mar 27, 2013 #6
    Well, depends ón how meticulous you are...;-)
     
  8. Mar 27, 2013 #7
    On*
    My apologies
     
  9. Mar 27, 2013 #8
    All risk is of course calculated.
    Even with gravitation, for pratical issues Newton's law is fairly used because it is a very good approximation, and a 5cm error when computing the position of the moon is not a big deal.
    The thing is, when dealing with a problem one has to evaluate in what regime the problem undergoes. Sometimes the system always stays in a classical regime and it is a very good approximation to use non-relativistic results.
    Of course when in doubt use the complete theory and then proceed to evaluate the contribution of relativistic corrections to see of their importance.
    For theoretical purposes, always use the complete theory, and then compute in different regimes if necessary. I would say this is a kind of 'common sense' aproach.
     
  10. Mar 27, 2013 #9
    So:
    Suppose one is examining the hydrogen atom and one is in doubt whether to use the Schrodinger or the Dirac equation. Would one then proceed with the Dirac or, if only the low energy states are of interest, use the Schrodinger?
     
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