Inescapable horizons

I sympathize with Herman. It's hard to give very specific advice, because that often entails much more responsibility, it calls into question many personal biases. For some years, believing this has made me refrain from giving specific advice. Nowadays I have developed a strong enough opinion that I don't care that I am biasing others to become more like me.

With this warning in mind, and perhaps some of this is the wine speaking through me, I suggest the following. My experience with you suggests to me that you like thinking about abstract ideas, that philosophy is important to you. While experimental physics also involves thinking abstractly, and you will find yourself in intimate contact with nature, it is very limiting in the scope of ideas you will explore, you will develop a very personal relationship with a smidgen of reality. Theoretical physics trades practical intimacy with breadth of appreciation, both of physics and of philosophy. I somehow imagine it will suit you better. I am offering you extremes in interpretation, they are admittedly broad generalizations, and I know excellent exceptions who straddle both realms. A rare species, whose company I inestimably value. 

I suggest instead of doing a thesis in both experimental and theoretical physics, you might consider other fields in theoretical physics. I imagine undergraduate education as a chance to unabashedly explore all curiosities, where specialization may even be frowned upon. Certainly I frown upon it, as I frown upon inescapable horizons which I can only delay in meeting.