Why are fermion-only or boson-only systems easier to study than mixed states?

[Tio Barnabe]

In general, is it of more interest to consider multi particle states consisting of fermions & bosons or multi particle states consisting of only fermions (or only bosons)? I have seen that if it's of the latter type, then the study becomes in certain way more easy to carry on, though the former seems to be more general.

 

[hilbert2]

If you're considering spontaneous emission from excited atoms, you have to include both electrons (fermions) and photons (bosons) in the model. Same applies when studying electron-phonon interaction in condensed matter physics.

 

[Tio Barnabe]

Thank you.