  We consider closed immersed hypersurfaces evolving by surface diffusion flow,
and perform an analysis based on local and global integral estimates. First we
show that a properly immersed stationary (\Delta H \equiv 0) hypersurface in
\R^3 or \R^4 with restricted growth of the curvature at infinity and small
total tracefree curvature must be an embedded union of umbilic hypersurfaces.
Then we prove for surfaces that if the L^2 norm of the tracefree curvature is
globally initially small it is monotonic nonincreasing along the flow. We also
derive pointwise estimates for all derivatives of the curvature assuming that
its L^2 norm is locally small. Using these results we show that if a
singularity develops the curvature must concentrate in a definite manner, and
prove that a blowup under suitable conditions converges to a nonumbilic
embedded stationary surface. We obtain our main result as a consequence: the
surface diffusion flow of a surface initially close to a sphere in L^2 is a
family of embeddings, exists for all time, and exponentially converges to a
round sphere.
