I'm curious what the hardest-to-understand areas of physics are. I'm in the second year of a physics degree, and I'm curious what might become difficult. I've been able to understand both special and general relativity. Later this year I'll be learning quantum mechanics, particle physics, solid-state physics, and the Schrodinger equation.
Which of these topics am I most likely to struggle with (keeping in mind I already understand general relativity)?
I'm curious as to why people think you have to be really smart to study physics. Not to say I'm not, but I wonder.