Very often we see people doing research on a completely different topic than was their undergrad major. How do they do it? How do they get an admit in an unrelated domain?<p>Once they get admitted how do they learn the new field? Solely self study from books?
The folks I know who have done it either already had the pre-reqs in their undergrad transcript, or went and took the missing classes before getting admitted. When I talked to schools about it (a long time ago), that is the answer I got as well: "Go take these courses and get a B or better, and then apply."
Often the people who did this kind of thing do most of their actual learning by themselves. That's not to say they don't learn from school, they do. The school part is very helpful to fill gaps. In graduate school it can be the same way. You are allowed to take graduate level school courses. It's also normal that you can quickly get up to speed by taking some 400 level undergrad courses in your new area after you have been accepted to the program. Once the actual new research begins, the things you learn for your research project are from reading papers like on arxiv and by doing your own experiments, so continuing official coursework doesn't matter so much at that point.
I’m currently doing a MSc in a totally unrelated topic to my undergraduate. They accepted some relevant professional experience I had as an alternative to a relevant degree (it’s been ~10 years since my UG)