I have a physics degree, and struggle with it too. Granted, my degree was 30 years ago and I've been working in industry, so I haven't maintained my theory chop

I have a physics degree, and struggle with it too. Granted, my degree was 30 years ago and I've been working in industry, so I haven't maintained my theory chops. The way it was explained in our graduate QM class was that certain operations in QM theory only work in Cartesian space. This is probably an over simplified statement of a Hard Problem, which is that QM and gravitation are both known to be exquisitely accurate theories, but mutually incompatible.