An excellent way to begin the process is to see what's been done before. Here are electronic versions of the final MPS402 proposals of previous Wells graduates: Past MPS402 proposals. And to see the final MPS403 theses, again in various electronic formats: Past MPS403 theses.
Please expect to have multiple worthy ideas as you go. As you follow up on your preliminary digging in journals and other sources, promising threads of inquiry will emerge. Some threads will lead "backward" (downward?), getting at the historical underpinnings of your subject. Others will go "upward" toward newer developments. Some will be dead ends . . . By gathering feedback from the other students in the class and in collaboration with me and other MPS faculty, and by your own brainstorming, you will close in on proposal topic.
Do I Have to Do "Original Research"? At this stage (MPS402), you most likely won't do that (not to say you won't learn plenty of new things, because you will). Most of your research will be learning what is already known about your subject area, as you refine the topic. In MPS403, your eventual thesis will be something completely new, to you and your fellow MPS students. You might set up a physics experiment and take data: your thesis would be presentation and interpretation of the data, along with a thorough review of the physics/engineering theory behind your experiment. You might take on an investigation into some knotty mathematical area; in your thesis, then, you would clearly present what is already known, and what you've learned. If you are interested in computer science, your research may become development of some kind of computer software application, possibly internet-based. We have also had successful thesis projects devoted to study of education and teaching in the MPS concentration areas.
What is the Role of Other MPS Faculty? Essential. Make use of our expertise (and not only MPS faculty's: build relationships with, for example, social scientists, education faculty, and other scientists at Wells and elsewhere!). You will be expected to collaborate, on an on-going basis, with at least one other MPS faculty member.