let's say, hypothetically, that i was doing my phd dissertation on only one of the next topics: 1.Metamathmeatics (model logic,proof theory,set theory,recursion theory). 2. Pure Maths (Algebra,Analysis,Geometry/Topology,Combinatorics,Number Theory). 3. Mathematical Physics &/or theoretical physics (cosmology,quantum gravity,chaos). and I recieve my phd diploma, let's say afterwards i would be doing a postdoc, and gradually getting to be a reasercher in academia, would my speciality in one of the above subjects harm any chance of me to also research in other subjects, or when you choose your narrowed speciality you cannot also contribute to other fields, i mean by writing articles etc. this is only a hypothetical question, i don't think that iv'e even touched the tip of the exciting questions in the above fields, and above all my ignorance is obviously showing, but at least i have a great deal of enthusiasim towards the fields mentioned above, perhaps not to specialise in but at least be of interest to me. p.s you may assume im daydreaming but in hypothetical type of questions you can do so. [;-)].