<p>" i just want to know if majoring in physics at princeton will allow me to be a string theorist (or something in that line) as easily as theoretical physics major would at cornell. "</p>
<p>That's something you're going to have to figure out for yourself. Most of us have no idea what string theory is in the first place (although, didn't they just talk about that on Joan of Arcadia?), let alone if a school is good at it or not. Chances are you are going to need grad school anyway; were I you, I would probably do Princeton Physics undergrad, and then Theoretical Physics Cornell for your grad program.</p>