I have worked in a lot of disparate fields from plasma physics, to nonlinear dynamics, to posture control, to neuroscience, to inflammation, to obesity, to gene transcription, and population genetics. I have had a lot of fun doing this but I definitely do not recommend it as a career path for a young person. I may have gotten away with it but I was really lucky and it certainly carried a cost. First of all, by working in so many fields, I definitely lack the deep knowledge that specialists have. Thus, I don't always see the big picture and am often a step behind others. Secondly, while I am pretty well cited, my citations are diluted over multiple fields. Thus, while my total H index (number of papers where number of citations exceeds rank) is pretty decent, my H index in each given field is relatively small. I thus do not have much impact in any given area. To be taken seriously as a scientist, one must be a world expert in something. The system is highly nonlinear; being pretty good in a lot of things is much worse than being really good in one thing. There is a threshold for relevance and if you don't cross it then it is like you don't exist.
However, if you do want to work in a lot of fields, the worse thing to do is to say, "Hey I really find field X to be interesting so I'm just going to read some books and papers on it and try to do something." I have reviewed quite a few papers, where some mathematician or physicist has read some popular science book or newspaper article on the topic and then tried to publish a paper on a problem mentioned in the book. I then have to tell them to read up on four decades of previous work first, and then resubmit. The way I have managed to meander through multiple fields is that someone will either contact me directly about some specific question or mention something to me either in a casual setting or at a conference. I could not possibly have made any progress at all if I didn't have great collaborators who really knew the field and the literature. Still, people constantly ask me if I still work in neuroscience, to which I can only respond "Just because you don't cite me doesn't mean I don't publish!"
