I'm in my 3rd year and I just switched my major over to computer science from physics, as this allows me to keep my career options much more open. This means I've already taken the required lower division math/physics classes for a physics major.
Now, I know it'd be hard to get accepted to a physics PhD program from just a CS B.S., but could I at least get into some lower level Masters programs in physics (maybe with a computation physics emphasis?) if I decide that physics is what I really want to do post-graduation?
I'm doing undergrad in Northern California at a UC, if it helps.