I am in my fourth year of BS-MS course in Physics in India. I will be applying for PhD next year but I do not have a specific topic in my mind.
Until now I have done 2 projects on Cosmology (related to Dark Matter in specific). Right now I have started a project on Semi-Classical gravity, which has been mostly reading work until now. I have liked both topics. I am also being introduced to QFT, Particle Physics this year which also look interesting.
So I do not know what should do my PhD in. Is it necessary for me to pin point my topic of my interest within next 1 year? or Is it fine to have "Theoretical Physics" as my topic of my interest?
As of now I planning to do my MS thesis on Semi-Classical Gravity so that I'll be able to explore a new topic as well as do something that I like at the same time. Is it necessary for me to decide my Master's thesis based on my potential PhD topic?