The Lanthanide contraction which is the decrease in ionic radii of the elements in the lanthanide series from atomic number 57, lanthanum, to 71, lutetium, is due to poor shielding of the 4f electrons which decreases the radius. It is also known that the relativistic effects make the core orbitals (s,p) contract while the f and d orbitals expand. How does this "relativistic effect" leads to the contraction of these orbitals which lead to Lanthanide contraction?