At first I didn't think this was an unusual interest, but seeing as we're 60 replies in and no one's mentioned it yet...either it's DEFINITELY unusual or it's so common that no one wants to mention it. I hope for the former.
QUANTUM/FUNDAMENTAL/THEORETICAL PHYSICS...!!
It's actually been an interesting topic to me for a long time (an entire subset of characters in my magnum opus are named after subatomic particles and other quanta...and I started that back in middle school).
I don't pretend to be an expert or anything, though...that's what kinda gets me about this thread; everyone seems to know so much, and all my interests are mostly surface-level or worse...part of the reason I keep coming back to quantum physics is because every 2 or 3 years I forget half the stuff I learned last time...6_6;
Anyway, I think what's most interesting to me about it is that it's all made up. ^^ A large portion of science is made up, actually (although few people like to address it) but it really sticks out in quantum physics. Like, if you understand what you're reading, it's hard to ignore the fact that it's all just different ways people imagined to break down the entire universe into elemental parts, and explain everything that happens in it, and THEN look for proof...it's insane. I can't imagine actually working in the field...
...But as a hobby, it's kind of something I do all the time. Whenever I write fantasy stories with very deep magic systems (which I do at least once a year) I'm always thinking about how I can use whatever paradigm I came up with to explain the existence of the world, either for worldbuilding purposes, or just for fun...theoretical physics is basically that, but with math. ^^
Hmmm...writing this has motivated me to finally look up string theory:
I'm biased towards QCD (I could blame school because that's what you learn there, but all the little particle names are just too cute...I don't want to live in a universe without neutrinos and gluons~) but string theory is actually kind of cool...people just don't explain it well.
They go 'so everything is actually made of strings' like it's some kind of flying spaghetti monster nonsense, but at its core its really a matter of dimensional perception...if I'm understanding it right (^^;;; ) everything we see represents only one dimension of the strings: like if you're looking at a real string head on, all you'll see is a tiny dot, a cross-section.
The cross-section of the theoretical string is a particle, with mass and energy...and I guess the idea behind it is that, by extending these particles into the 1st dimension and looking at them as merely parts of strings, we can explain a lot of phenomena.
If you enjoyed this small peek into the world of theoretical physics, I implore you to look it up; the fun (literally?) never ends~. I usually just surf Wikipedia, the info there is at a good level for me...it's important to find a source you can actually understand (scientists have a tendency to jargon you to death...90% of us don't care about teaching things to laymen, and it's such a shame).