  As Phil Anderson noted long ago, frustration can be generally defined by
measuring the fluctuations in the coupling energy across a plane boundary
between two large blocks of material. Since that time, a number of groups have
studied the free energy fluctuations between (putative) distinct spin glass
thermodynamic states. While upper bounds on such fluctuations have been
obtained, useful lower bounds have been more difficult to derive. I present a
history of these efforts, and briefly discuss recent work showing that free
energy fluctuations between certain classes of distinct thermodynamic states
(if they exist) scale as the square root of the volume. The perspective offered
here is that the power and generality of the Anderson conception of frustration
suggests a potential approach toward resolving some longstanding and central
issues in spin glass physics.
