Steve Carlip says this [back in 2007], here,: http://www.2physics.com/2007/06/symmetries-horizons-and-black-hole.html "...Until fairly recently, no one had a clear idea of the microscopic states responsible for black hole entropy. Today, we suffer the opposite problem: we have many explanations, each describing a different set of states but all agreeing on the final numbers. .......  One attractive possibility is that a hidden symmetry of classical general relativity controls the thermodynamic properties of black holes. ......  The uncertainty principle prevents us from simply saying,"A black hole is present." [Instead, we must find a way to impose constraints strong enough to ensure the presence of a black hole,but weak enough to be allowed by quantum mechanics.] . ...... The key point is that the horizon constraints break the fundamental symmetry of general relativity, general covariance (technically, diffeomorphism invariance). [As a result, states that would normally be considered equivalent, differing only by a "gauge" transformation, are now physically distinct.] [The brackets are not Carlips and are included for perspective.] Is this area of research active: 'hidden symmetries in GR???' and has it produced anything interesting....Is it known by maybe a different term today?? Any suggested reading sources?? And what in layman's terms do 1,2,3 mean??? Wiki had nothing I could find under "Symmetry in GR". I just got Taylor and Wheelers' "Exploring Black Holes, Introduction to GR" an hour ago in the mail and there is nothing in the index there about symmetry in GR. edit: Wikipedia makes mention: "In general relativity, the symmetric stress-energy tensor acts as the source of spacetime curvature... " thank you.