In physics, your solution should convince a reasonable person. In math, you have to convince a person who's trying to make trouble. Ultimately, in physics, you're hoping to convince Nature. And I've found Nature to be pretty reasonable.
Frank WilczekIn physics, you don't have to go around making trouble for yourself - nature does it for you.
Frank WilczekThe answer to the ancient question Why is there something rather than nothing would be that nothingis unstable.
Frank Wilczek