Embedded structure in quantum theory, functional operator and multiverse

Abstract

We explore a wider theoretical framework that has quantum field theory built-in, taking the fact that quantum mechanics is reconstructed from quantum field theory as a hint. We formulate a quantum theory with an embedded structure by introducing functional operators, and we find that it could describe the level II multiverse. Topics related to a beginning of the universe such as an inflation, the third quantization and the landscape are discussed in our formulation.