Maybe you can't commit because these fields are so similar? They're all analytical, and for example mechanical engineering is just applied physics and physics i

Maybe you can't commit because these fields are so similar? They're all analytical, and for example mechanical engineering is just applied physics and physics in practice is often about programming simulations and data processors. So, in a way, it doesn't matter that much what you choose, as these fields have very similar "feel" to them, and also you can fairly easily change fields in the future.