Time Travel, Quantum Entanglement and Quantum Computing

Chapter 2 of Peskin and Schroder 'An Intro to QFT' contains something like this:Just as in ordinary quantum mechanics, we look for eigenfunctions of momentum and energy:ϕ(x)=e−ip⋅x\phi(x)=e^{-ip\cdot x}ϕ(x)=e−ip⋅x wherep⋅x=pμxμ=Et−p⋅xp\cdot x…