I will be applying to graduate school this coming winter, and I'm having difficulty deciding what field I should be directing my effort towards. My background: I have a bachelor's a physics, and my senior project was to write an N-body program that simulated galaxy collisions with the inclusion of dark matter. I've also tackled several other physical problems at my job, such as simulations of sensors, simulations of magnetic fields, etc. My main interest: Computational simulation of physical systems. The main issue I have is that I feel I would be content designing simulations of almost any physical system. I could focus on galaxies, traffic flow, hurricanes, molecular interations, field calculations, etc, anything where I get to model reality in a virtual environment. I don't think that computer science is the way I wish to go. I am interested in the theoretic side of the actual problems, not the most efficient way to code. I feel that coding efficiency is something that I can pick up by myself. So I guess my question is: How should I apply? Should I apply very specifically to a certain field that is deeply dependent on computational simulation? Or should I apply broadly, and not really show preference to any particular sub-field?