Hello I’m a freshman in high school extremely motivated by physics and really enjoy it. I plan on taking AP physics C next year and I want to get a job in physics. Not sure which branch yet but theoretical physics seems the most interesting to me so far. What must I do to become a theoretical physicist and how difficult is it?
Welcome to CC.
What math courses have you taken? AP Physics C (especially the E&M portion) is generally considered the hardest course at most high schools. Familiarity with calculus would be very helpful but not absolutely necessary (Newton invented calculus after all).
Theoretical physics is probably the hardest subject there is (I may get some arguments from some mathematicians). Theoretical physicists are working on the thorniest and the most difficult problems in the world: to explain and predict how everything works in the universe, accurately and consistently.
The best books to learn physics, IMO, are still the The Feynman Lectures on Physics. Feynman is one of greatest theoretical physicists of all time. He had a knack for figuring out and explaining how things work physically and intuitively, without relying on a bunch of formulas.
For a biographical sketch of the physicist named above, you may want to read Surely You’re Joking, Mr. Feynman!.
AP physics C assumes that the student is at least concurrently enrolled in calculus.
In college, introductory physics for physics majors tends to require more advanced math than AP physics C. For example, the course with E&M typically lists multivariable calculus as a corequisite.
In any case, the minimum high school prerequisites to major in physics in college are precalculus and high school physics. However, it appears that you will be well advanced of that already if you are ready to take AP physics C and have or will take calculus.
^Prerequisites and/or corequisites aren’t always strictly enforced at all high schools. Exceptions can be made if the teacher feels the student is capable of taking that class.
The number 1 most important thing IMHO is to get a solid foundation in math. You do not need to jump ahead. A minimum would be to be ready to take calculus when you arrive at university. Marginally better would be to take calculus by your senior year of high school. However, what is important is to do very well in your math classes. You want to really understand what you are doing. Physics makes a lot of use of math, and you want to know math well. When you get to special relativity you will begin to understand what I mean.
My second suggestion is to get to AP physics C by your senior year of high school. Again I do not see much reason to jump ahead. More important is to do very well when you get to it.
Remember that life is not a race. You are young, you have plenty of time, and you really will be a stronger student in two years than you are now.
You should also look for summer programs and other extracurricular enrichment programs for high school students on the topic of physics.
You can also reach out to physics professors in your local colleges and universities. They would mostly be very happy to talk to you.
Good luck!!
I agree that there’s no need to rush. To become a theoretical physicist is a long long process. There’s so much you have to learn and AP Physics C is not even a blip on the radar.
Oh. I’m taking AP calculus BC right now and I’ll be taking Multi Next year with my course load. Check out my other post if you want to see my classes and thanks for advice 
Check my other post with all my classes im taking next year and then help me out here.