Some physics topics captured my interest long before I took the required coursework. On such happy occasions, I read ahead and solve problems. Sometimes, I do the preliminary reading and problem solving months or semesters before taking the course where that topic is discussed. But to do that, I need a good source on what textbooks to use.
This is where MIT's Open Course Ware comes in. It's a website offered by the Massachusetts Institute of Technology containing course materials used by their Professors. Aside from the course descriptions, you can also find the syllabus, the reading assignments, homework and exams, and lectures or lecture notes. Sometimes the relevant pages will contain the schedules of topics discussed each meeting. This gives me an idea of what the pace is in that school.
Not all of the courses will have OCW pages, nor will all courses have all of the above. For example, some courses, such as Professor Lewin's physics course, 8.01 (the introductory physics course) contains videos of the lectures, while other course pages will have no multimedia content. But enough is provided to get a flavor of the course, and the most important information is the choice of textbooks, and the problem sets. For a student in a developing country, this is important, since it allows me to compare what is offered here with what the rest of the world has to offer. I learned from OCW what is expected of a typical undergraduate or graduate student.
When I first wanted to study general relativity, I got wrong-headed advice from a friend on what the best textbook was. (The recommendation, by the way, was Weinberg's text.) I couldn't learn it from that book because there were no problems for solution; it was also a textbook for graduate students, so it was at the wrong level. I had to go through a sequence of books before I found a good one at the right level . This was Bernard Schutz's A First Course in General Relativity. Although it provided some formalism, I felt that my ability to see the results at a glance was still in need of remediation.
It was at around that time that I first learned of OCW. To remedy the lack I felt, I looked up the introductory relativity course, 8.224 . I organized a study group with some fellow undergraduates. We obtained copies of Taylor and Wheeler's textbook Exploring Black Holes, and we worked through it. ( I still have my solutions to all of the questions filed away, in case I get to teach an undergraduate course in relativity.) My current research is an outgrowth of the things I learned from 8.224 and the graduate level course 8.962.
Sometimes, I wander around the other archived courses. I've used materials from the complex variables course, 18.04, when teaching methods to undergraduates. I'm happy that the methods we learn is standard, although we go more into the theory of gamma functions instead of studying integral transforms (which is taught anyway in the regular methods courses).
I've read the biographies of some well-known scientists, and many of them are good at learning things on their own. But without knowing the necessary books, self-study may be doomed to failure. A sequence of lucky accidents is required before it works. I know of cases of otherwise intelligent people who were just unlucky; Without mentors, without access to online resources (this was years ago, before internet access became something taken for granted), they were lost from the world of theoretical physics. Their talent was wasted.
My collaborator is luckier than I am because OCW gives a good list of introductory general relativity texts. No more wandering around the library shelves. (Although this has its own disadvantages!) As a result, general relativity can be understood by a well motivated sixteen year old. Compare this to Eddington's time when it was claimed that only few people understood general relativity!