Why is it that all the potentials that we use in QM are classical ?

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SUMMARY

The discussion centers on the use of classical potentials, such as the Coulomb potential, in Quantum Mechanics (QM). It highlights that while QM employs classical Hamiltonian observables, the second principle of QM allows for quantization of these observables into self-adjoint operators on Hilbert spaces. Notably, in Quantum Field Theory, potentials can indeed follow wave equations like the Klein-Gordon equation. The conversation also touches on the complexities of retarded interactions in classical electromagnetism and their implications for quantum systems, including phenomena like the Lamb shift and the anomalous magnetic moment of the electron.

PREREQUISITES
  • Understanding of Quantum Mechanics principles, particularly quantization.
  • Familiarity with Hamiltonian and Lagrangian mechanics.
  • Knowledge of Quantum Field Theory and wave equations.
  • Basic concepts of classical electromagnetism, including potentials and retarded interactions.
NEXT STEPS
  • Study the Klein-Gordon equation and its applications in Quantum Field Theory.
  • Explore the role of Feynman diagrams in Quantum Electrodynamics (QED).
  • Research the Lamb shift and its significance in quantum physics.
  • Investigate the relationship between classical and quantum potentials in various physical systems.
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Physicists, quantum mechanics students, and researchers interested in the foundational aspects of quantum theory and the interplay between classical and quantum potentials.

trosten
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Why is it that all the potentials that we use in QM are classical ? For example the columb potential. Shouldnt we use a wave equation for the potential as well as for the position?
 
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trosten said:
Why is it that all the potentials that we use in QM are classical ? For example the columb potential. Shouldnt we use a wave equation for the potential as well as for the position?

Because it's natural..?? :confused: It's the idea of quantization.Describing interactions at quantum level by means of mathematical objects requiredby the formalism of QM.The second principle of QM (the postulate of quantization) says that for observables with classical correspondent (the spin angular momentum is an example of quantum observable which does not have classical correspondent) we do the quantization by passing all classical Hamiltonian observables viewed as functions from the Poisson algebra of Hamiltonian observables into densly defined self adjoint linear operators acting on th separable Hilbert space of states (defined in the first principle/postulate).
So everything has 'classical' roots.The notions of Hamiltonian,Lagrangian,action,field equations,energy,angular momentum,momentum,evolution operators,...Except spin.

Daniel.
 
Actually, in virtually any Quantum Field Theory the "potential" does obey a wave eq (like a Klein-Gordan Eq.) And, in classical E&M, potentials must be supplemented by vector potentials as well. The interaction between two charged particles is described by retarded forces/potentials, and thus requires two times. The plain fact is that the math of the retarded interaction is horribly difficult. The classical E&M potential give solvable dynamics for both classical and quantum systems. And the Coloumb Potential gives the basis in QM for a remarkably accurate description of atomic properties and dynamics.

Phenomena like the Lamb shift or the anomalous magnetic moment of the electron can be thought of as coming from a "wave description" of interactions. They involve charges absorbing radiation that the same charge emitted. QED, past lowest order approximations, is exactly a theory with interactions that can be described in terms of wave equations. But we tend not to think along those lines, and more often than not, we tend to think of QED in terms of Feynman diagrams.

Regards,
Reilly Atkinson
 

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