>>12163415When you say you want to study at an "advanced level" do you mean you just want to learn theory, or do you mean you want to learn that theory and be able to work as a physicist?
You can do the former by looking for the course requirements of an undergraduate physics student at a major university, then following the reading material as listed in those courses' syllabi. Then you can start looking into graduate courses in your area of interest, and likewise start looking at research articles. It's probably a good idea to look at older, more foundational papers on a topic, since without guidance you're likely to be lost on highly technical papers on (more) mature and particular subjects. You can also find free online courses online from places like MIT.
If you want to be a physicist, you'll need a university degree.
