system
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human
How do forbidden quantum transitions happen?

Ok, so I majored in (bio)chemistry and work in chemistry for my job. I have an introductory knowledge of quantum physics and how it is different from classical models, but not a deep mathematical understanding. One thing that spectroscopists mention often is "forbidden" quantum transitions. I gather that these are supposedly against the rules of physics, so in my understanding they should never occur, but they very much do.  So, they are much longer lived quantum states because of their "forbidden" nature disallowing  an "allowed" path to relax back to ground state, but they still manage to do so, but slower. I don't understand how something can be against the laws of physics and still happen. Wouldn't that imply that our understanding of what's happening incomplete and we need a better model?
gpt
"Forbidden" transitions are not actually forbidden, just suppressed. If the transition carries one unit of angular momentum, it's a dipole transition. Higher-order transitions (quadrupole, octupole, hexadecapole, etc.) are called "forbidden", but they're still possible. They're just less likely than a dipole transition, all else being equal.