gwyn@BRL@sri-unix (09/06/82)
From: Doug Gwyn <gwyn@BRL> Red-shifted light most certainly can "hide mass somewhere" if you're interpreting mass and energy as equivalent. Light has energy. It is not necessarily useful to try to track down the "location" of a given parcel of energy, since it may reside in a field for example. Better yet, there is no conserved quantity in general relativity that is entirely physical (tensorial) corresponding to the gravitational field. You can find a conserved pseudo-physical quantity, and call a portion of it "energy of the gravitational field" if you so desire, but this is a dangerous practice for theoretical work since there is no physical quantity with properties normally attributed to energy.