Right now I'm applying for a masters degree in physics with photonics. It is an area that I find very interesting, and I've seen other options that are in the physics degrees (e.g. applied nuclear physics, advanced quantum physics) that are also interesting and I'd plan on taking when I'm on my degree.
I'm also very keen to study General relativity, but I am also very, very aware that you need to be pretty damn good at maths to be able to do general relativity.
What I'm wondering is if I'm able to study areas of maths and physics after I've completed my degree so that I will be able to tackle general relativity.
Just as a side note, I am applying to British universities, just so you're aware if there are any differences in the way the university system works where ever you are from.