Existing literature on signature change considers the change surface to be space-like. We construct a new model for signature change based on the signature-changing hypersurface in the beginning of the universe being a null hypersurface. This affects most quantum cosmological considerations, since in quantum cosmology, according to the Hartle–Hawking no-boundary proposal, the creation of the Universe occurred along a space-like 3-hypersurface. Based on this assumption, junction conditions for the signature-change hypersurface are derived and the corresponding results are explained. The energy–momentum of the change surface is non-vanishing and the result for pressure of the change surface is in agreement with inflationary scenario.
