I'm still an undergraduate but I was wondering about the future and all that. I do like love physics as a whole, but I don't think there is a subfield which I REALLY like or REALLY dislike. I also like "versatility" as a way of life. So I was wondering: "can I move to and from subfields as I please? " For example: Can I take an internship in astrophysics, take a master course in Statistical Mechanics and then a PhD in Mathematical physics? Or whatever other sequence, with whatever other subfields. As a bonus: is it possible to, after PhD, make research in yet another area?