# Do you use QM in Conjunction With QED/QCD?

Staff Emeritus
Do you still use QM in conjunction with the other theories? Is QM kind of like the basic theory that the others rely on? (Hopefully those questions make sense)

QED and QCD are specific quantum field theories. As a subject, quantum field theory is a subset of quantum mechanics: quantum field theory is the quantum mechanics of fields. QED is the quantum mechanics of the electromagnetic field. QCD is the quantum mechanics of the color field.

Staff Emeritus
Do all the standard QM rules apply to QED and QCD?

Yes. But what in particular are you thinking of as "all the standard QM rules"?

If you define electrodynamics to be the study of matter with the electromagnetic field (i.e. with photons), then QED is simply a fully quantum-mechanical approach to that study. In that sense, the "standard QM rules" apply since what you're doing is simply applying QM to yet another problem.

One caveat to this discussion is that the Born interpretation of the wavefunction becomes a bit shaky. The reason is that in quantum field theory (QFT), particle number is not necessarily conserved. This is of little concern because what we would normally call a wavefunction function in single-particle QM yields calculable results in QFT for things we actually measure like scattering experiments, etc.

bapowell