Vierbein walls in condensed matter

The effective field, which plays the part of the vierbein in general relativity, can have topologically stable surfaces, vierbein domain walls, at which the effective contravariant metric is degenerate. We consider vierbein walls separating domains with flat spacetime which are not causally connected at the classical level. The possibility of a quantum mechanical connection between the domains is discussed. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 11, 705–710 (10 December 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.