Courses Should I take advanced courses as a physics undergraduate?

[YSM]

I am a third year undergraduate physics student with some interest in theoretical physics. This term I want to learn General Relativity or Group Theory, but they are all hard, time-consuming courses. If I don't take them, I can explore broader areas of physics to make a decision on what I will focus on in the future, or go to get some reseach experience for my undergraduate school admission, which I will have less time to do if I take those courses.
If I take those courses, well...I have knowledge of group theory and GR, that may be an advantage sometime. And those courses can prepare me for a theoretical physics PhD, though I have not make up my mind for it. Anyway I am interested in them.
In general, it is a choice between learning broader or learning deeper, or textbook learning V.S. research experience, or self-interest V.S. graduate school admission.

 

[fresh_42]

This is not easy to answer without knowing the many specific things about your situation, goals, university, country etc. etc. So please be aware of the fact, that all answers you might read here, cannot be taken other than a general view from some outsiders.

The first thing I thought of was: Well, group theory can be learned from a good book without taking a lecture, whereas GR probably not. At least if you mean by group theory the usual finite ones. If you mean the various different linear groups, which are far more important in physics, then a lecture can be valuable. So the question is: do you need a document which proves your attendance or not? Otherwise you could just attend GR and learn (finite) group theory whenever you have time to do so.
My second thought was: experiences in research - what does that mean? Experience in laboratory work, I'd say yes, yes, yes. But what is research? How to use a library? However, if it is expected in a way as it sounds to be, then you should do it.

In general there are good reasons a curriculum is as it is. You might lose interest if a subject comes too early, means is too hard if the mathematical knowledge needed isn't at the necessary level, yet; or if the work load will be too heavy. These are factual criteria, your argument to have time to consider where you want to go to is not. The contrary is true: the more different areas you study, the better you will know what suits you and where your interests and limits(!) lie. But don't overload!

There's another aspect. Some students want to get through as fast as possible, e.g. to make money or to have a better vita as a post-doc, whereas others want to learn as much as possible. These are conflicting goals. You should answer this question for yourself before you make a decision. If your goal is a PhD in theoretical physics, then you will have to study GR anyway - at least in my understanding, although I'm sure this is not automatically the case.

Long story short:
You will need a lot of math for GR. Are you prepared?
It will cost you spare time. Are you prepared?
Will it also extend your study as a whole? The duration of a study has consequences: in an economic career as well as in academic one!
What will it cost, if you will not have this "research experience"?