Classical unified field theories to isospin rather than electromagnetism; this is related to a discrete (or ""internal"") symmetry known to Einstein as "displacement field duality". Einstein became increasingly isolated in his research on a generalized theory of gravitation, and most physicists consider his attempts ultimately unsuccessful. In particular, his pursuit of a unification of the fundamental forces ignored developments in quantum physics (and vice versa), most notably the discovery of the strong nuclear force and weak nuclear force. Inspired by Einstein's approach to a unified field theory and Eddington's idea of the affine connection as the sole basis for differential geometric structure for space-time,
Unified combatant command the space-related responsibilities previously assigned to the Commander, United States Strategic Command; and (3) the responsibilities of Joint Force Provider and Joint Force Trainer for Space Operations Forces". A sub-unified command, or, subordinate unified command, may be established by combatant commanders when authorized to do so by the Secretary of Defense or the president. They are created to conduct a portion of the mission or tasking of their parent geographic or functional command. Sub-unified commands may be either functional or geographic, and the commanders of sub-unified commands exercise authority similar to that of combatant commanders. Examples of current and former