Today, more than 80,000 Americans are in solitary confinement. Explorer looks at the science of solitary and discovers what it means to be absolutely alone. We go inside Colorado State Penitentiary (CSP) and witness prisoners on the edge and the guards who watch over them. Then, we look at experiments on whether isolation dramatically alters behavior and ongoing new research on how solitary actually could cause long-term mental problems like paranoia, disorientation and delirium.  (50 minutes)