I am a PhD student in physics at a US institution. I've worked with a very good and supportive professor last summer in some area of research. The goal was to try a particular research group and see if it is a good fit. I was not committed to that group. The research work in that group is very much focussed on a particular method of computer simulations.
Now, I discovered that I am extremely interested in a different field of physics, which is much more theoretically oriented. I find that I am naturally much more capable of doing pure theory work in that other field of physics. I have to decide on which field I should be doing research on next spring. I found that all professors working on the field I am very interested in are not available next spring. At least one of them will take students next September though, but he still has to decide on which student he would take.
I am still very interested in one of the research questions that I started to think about last summer with the original group. The PI said he is available next spring.
My question: Would it be ethical to continue working with that group even though I know there's a possibility that I will switch fields next Fall? If I join, I intend to work as hard as I can on the project given to me, but I feel much more interested in (and capable in) the other field of research.