I'm better at cosmology than math, but I like math more, but cosmology is more practical. Which should I get a PhD in?

That other question got me thinking. IDK how wise it would be to get a PhD in both. Clearly I love math more than anything else in the world, but cosmology is equally fascinating (I just don't take it to the level I take math). It's also more practical in terms of direct usage, whereas lots of math is studied "because it's there," when the types of math I enjoy only have a little bit practical usage outside of physics. I really think that, even though it will be *really* tough, I have to get a PhD in both math (specifically topology and/or chaos theory) and cosmology (and QM, if I can). At this point, the only thing holding me back from being as smart as I could be is my horrible memory and this ADHD, which I hope goes away when I'm an adult. Hopefully these should improve and I can get working on some crazy new technology/theory :P