Constructing Non-Computable Julia Sets
  We completely characterize the conformal radii of Siegel disks in the family $$P_\theta(z)=e^{2\pi i\theta}z+z^2,$$ corresponding to {\bf computable} parameters $\theta$. As a consequence, we constructively produce quadratic polynomials with {\bf non-computable} Julia sets. 
Mark Braverman, Michael Yampolsky