Do graduate schools care about the subject for my undergraduate thesis? This is my first post!
I’m a junior who knows he will go to graduate school, however I’m not applying until next fall. Presently, I’m working on an undergraduate thesis which turns out to be very number-theoretic—I’m glad I have to opportunity to work with a professor on something like this, but my primary interests are categorical logic and homotopy type theory (both of which I’ve studied independently). Hence, not number theory! 
If I mention (on a grad school application) that my interests are the above (and that I haven’t done any actual research in them), is that going to look odd when juxtaposed with my thesis topic?
Basically, I don’t want them to think I’m misjudging my proficiencies in, say, categorical logic, if:


*

*My thesis does not provide supporting evidence.

*My letter writers can’t attest to the notion either.

 A: My personal experience with this is somewhat modest; I'm a graduate student (Msc) in mathematics myself though. However, I also know both several professors and students, whom I have discussed such topics with many times in the past.
I would say that, although it depends a lot on your department and the people handling your application (professors, advisors, etc.), the topic of your undergraduate does not matter that much per se.
What might matter more is the quality of your work, and that you work independently (but the quality of your work is not lacking because of your fear of asking for help), and you finish in time (the last one perhaps depending more on the situation).
At least at my department (being Scandinavia, and this may vary from country to country though; I am not that aware of academic culture abroad, however it seems to vary less so than other cultures I guess), much of the point of the undergraduate thesis is showing that you can work independently, organize your own thoughts into something coherent, of good quality, that is communicated to others, and that you actually finish what you started.
The subject being different from what you will continue doing can even be good, since it is always good to broaden yourself somewhat. Even if you think you are spending time on unimportant things, they will most surely come back to help you later. Also, this will perhaps even be see as something good in that sense by others, since you show that you have a certain range and can understand different topics. That being said, if the subject has to do with what you want to continue doing later, this of course also has its benefits. I sort of wish this had been my case, since I feel I know little about a lot, rather than a lot about little, which can be beneficial in a subject like mathematics.
To conclude, there are pros and cons, but they are more for your own knowledge/learning, and less for your direct career chances at this level. In the end, the subject won't matter that much for your chances of getting in. So, focus on the quality of the content, and on showing independent research skills.
Oh, and welcome to the forums!
