I don't think there's any reason you couldn't grow radishes indoors. I would be inclined to use a larger container than a soda bottle if you're growing them for the roots, as you will want to give them enough space to expand (you can also plant the seeds close together and harvest the young greens to eat). They'll need a good light source, either a sunny window or a grow light, and be sure whatever container you use has drainage holes in the bottom. Good luck, sounds like a nice winter project!
