How realistic to work in two different fields concurrently

[mathematicianwannabe]

I am a newly admitted PhD student. When I applied for this program, I stated several research interests in my SOP. In the end, I am assigned with a supervisor whose research interests overlap with mine a bit, but not the same as my primal interest. Unfortunately, I have become more and more interested in my primal field and less in my supervisor's. My question is, how realistic to work in both? There is a post doc who is willing to guide me to work in my primal interest field, but if he leaves one or two years later, then I am afraid the work cannot be continued. Plus, I am afraid I will not be able to meet my supervisor's expectation if I do not devote all my time to his project. Moreover, since I am partially funded by my supervisor's stipend, would he mind if I work on something else? The biggest concern is that, what are the chances that my work with the post doc can lead me to a post doc position in my primal interest field 4 years later? Thank you in advance for your opinions.

[MoJingly]

I find it strange that you were "assigned" a supervisor. Did you get any say in who it was going to be?

I would say that you should bring this up to him. Tell him your interests. It's better to get a plan right now than get a few years down the road and be stuck. Grad school is a balance between what you want to study, what people will support you in studying, and what is actually a reasonable undertaking.

Also, don't think that what you study in grad school will be what you end up studying forever. In fact, it probably won't be. Grad school is more training than anything. You're trained to think about relevant and important questions and then trained how to figure them out. Just a thought.

[Arcadian]

I find it strange that you were "assigned" a supervisor. Did you get any say in who it was going to be?

My understanding was that he listed several people in his SOP, and he was paired with one of them - but that just happened to be the person with the least amount of overlap with his interests. Initially he thought this person was a solid choice, but then he increasingly became interested in another topic (and less interested in his adviser's).

That's entirely possible, and a tricky situation. I think the best course of action depends on the discrepancy between your adviser's project and your desired project. Are they completely different methodologies, or are they just different topics in the same field? If it's the latter, I'd say you're fine to just focus on your adviser's work. You can always study that other topic later in your career. But if it's the former, then you have to really decide what you want to learn during your PhD and how you want to market yourself later in your career. Is your adviser's project setting you up to be a highly desired post-doc? Or is it holding you back from doing something that would be more beneficial for your career?