Please check my logic. 1. Feynman diagram is a tool to calculate 'final state' from an 'original state'. It is mostly used for simple processes, like scattering. 2. 'Final state' usually have a precise meaning due to observation of particles trajectories. 3. However, in MWI there is nothing special about measurement and evolution is unitary, so time of the 'final state' can be chosen arbitrary. 4. Also, (having an infinite computation power) we can shift time of the final state to, say, 1 day after the initial state. 5. So (again having infinite computation power) we take an isolated spaceship today and calculate its final state one day later in terms of MWI, which of course, contain different decoherenced 'branches'. However, as evolution is unitary, we can do it. 6. Traditional view of what is inside Feynman diagram between initial and final states is 'virtual particles' which are 'just math', just mathematical tool to calculate a final state. 7. However, an astronaut, lived that day on that spaceship, would definitely not agree with the claim that his whole day was 'virtual' and 'just math'