Ah yes, the paradox of choice (great book btw). Physics or Music? I would definitely combine the two.
The possibility's of doing something with those two are endless. Perhaps you could set some constrains to focus more on the problems you can solve within those boundaries.
Solve a problem for people in the future using physics and music.
Male? Grow a mustache.
Create a new musical instrument. You can only control it with physical forces (no touching). This would make a nice performance/installation. Magnetism, wind etc. Groovy.
Get drunk in the morning.
Redesign a classic game. The Tetris patterns are the drum sequencer patterns. Not to much physics involved though. Different game? Space Invaders with surround sound sound sound... sound.
Floss twice a day.
Okay, I'll stop before I derail myself any further
Questions to ask yourself:
Should it be screen based only?
Big project, small project?
What do I want/need to learn?
What's the concept/idea?
Does it amaze?