text: Although it has nothing to do with ergodic theory, any spherically symmetric solution to a set of equations name for this system must be static and asymptotically flat according to Birkhoff's theorem.
full_question: Although it has nothing to do with ergodic theory, any spherically symmetric solution to a set of equations name for this system must be static and asymptotically flat according to Birkhoff's theorem. The exchange of virtual photons between two otherwise uncharged plates placed in this system causes a net force in the Casimir effect. When the energy-momentum tensor equals zero in a region, the Einstein field equations are named for this system. For 10 points, what system consists of space devoid of all matter?
first_sentence: Although it has nothing to do with ergodic theory, any spherically symmetric solution to a set of equations name for this system must be static and asymptotically flat according to Birkhoff's theorem.