Hello! I'm new to this forum and joined, for now, specifically to ask this question. Long story short, I'm 33, I've loved physics and math since middle school, I got my bachelor's in physics from UC Berkeley, was planning to get a PhD in astrophysics/cosmology, but due to certain things decided i wanted to do something where i felt i was more directly helping people. So, instead i got a master's in medical physics (basically radiation therapy for cancer) and now work at a hospital. Up until recently, i was using my brain and being exposed to real physics by having to study for board exams. Now that i am finally done with those, i am super happy about it, but honestly i am missing doing something challenging to my brain day to day, as in daily clinical work there really isn't much physics. I don't want to leave this field as i do feel good about helping people (that's why i switched to it in the first place), but i would like to do something more intellectual on the side also, again preferably something that could make the world a better place (e.g. work on new energy sources or such) but also challenge my brain. Or, since i am getting out the "helping people" desire in my day job, I'd be cool with getting back into astrophysics and cosmology, but without a PhD it's not like i could really contribute much. I am even thinking of just reading some advanced physics textbooks on my own for courses i didn't take, such as general relativity, but again i assume i couldn't really do any research or publish papers without going back to grad school. Does anyone happen to have any ideas on what i could do or where i could start? Thanks!