I briefly double-majored in Computational Physics and Music Composition. I failed out of the music program, but was able to beg for C-'s to count for my General Ed.
I like to think I chose the two hardest majors in the school, but the music major was two orders of magnitude more difficult for me. I'm sure there's people for whom the opposite would be true, but I think an attempt at objective ranking would put the music degree as harder than the physics.
I majored in computer science, with classes in math, physics, linguistics, etc... but also spent about a year majoring in music. In my opinion, the music classes were harder, and I had been playing music since I was 6. It's intense stuff. It really is like a form of applied mathematics, and you have to not only understand it on paper with your eyes, but hear and understand it with your ears.
Mastering the basics is hard enough... being able to apply this knowledge creatively takes it to a whole other level.
I like to think I chose the two hardest majors in the school, but the music major was two orders of magnitude more difficult for me. I'm sure there's people for whom the opposite would be true, but I think an attempt at objective ranking would put the music degree as harder than the physics.