# Thread: spherically symmetric function

1. ## spherically symmetric function

Suppose f:R^3\(Ball of radius 1)--->R is smooth and satisfies f(S^2)=0, ie the unit sphere is a level set of f. does it neccessarily follow that f is a spherically symmetric function?

2. ## Re: spherically symmetric function

No. Why do you think so?

3. ## Re: spherically symmetric function

You said "the unit sphere is a level set of f". (Emphasis mine). It does not follow that there are not other, non-symmetrical level sets.

4. ## Re: spherically symmetric function

Yes i realised as soon as i went to bed that there are many counterexamples. it was just a hopeful leap on my part-i am trying to prove the equality case of the penrose inequality for graphs over R^3. Basically, i showed in my proof of the main part of the theorem that equality holds only if the domain of f isnt defined on some ball. i was then wondering if i could use this fact and birkhoffs theorem to conclude that the graph is in fact isometric to schwarzschild. thanks for your replies anyhow