AN EPIGRAM "The great wall of China..." F. KAFKA A wall around you- then, why a door? FERMI AGE THEORY When we are born, we know not where, or when we will die. How we wander around, while we are slowing down in a finite medium! Our scattering seems isotropic; and our average lethargy, Independent of energy. Valid is the Diffusion Theory. In every collision, we gain exactly an average lethargy. As we grow older, we have traveled more- the slowing down is zero a at a void; and, continuous at an interface.