Can I diet without exercise

Simply put, No you cannot. Without activity weight will not shift or change, it will just increase, as you are not urging your metabolism to do anything.

Just as if you were to starve yourself or skip meals, you would put on weight. Why? because your brain is telling your body to feed off your fat stores. When this happens, your fat cells swell up and hence why we put on weight when we miss meals or take out too many hours between Breakfast, Lunch and Dinner.

In other Words, you cannot have one without the other. They come together.