Borrowing from the Universe

Okay, so in a world of mine, I am basically making magic and science have no distinction, they are essentially one in the same. But what I want to do is keep the conservation of energy.

What do you guys think of being able to "borrow" energy or what have you from the universe (kind of like virtual particles)?

I'm still in the early stages of this system, but what are your thoughts? As for how you would pay back your dues I'm still not sure, but what do you think of it as a concept?