I always wanted to ask (but was afraid to) about the borders on the famous Feynman diagrams. As I understand, Feynman diagrams have the same age as Copenhagen Interpretation. So at that time it looked very logical: quantum behavior inside, but classical world outside. Outgoing particles are the particles ‘measured’ by some ‘measurement device’. Incoming ones – those coming from a reliable macroscopic source. Borders of the Feynman diagram separated quantum worlds from a classical environment. Shouldn’t that be modified when we know that there is no sharp line which separates both worlds: classical and quantum? Shouldn’t we see the Universe as one huge Feynman diagram – without any borders whatsoever? And what value, in that case, has telling if a particle is ‘real’ or ‘virtual’ by looking if it crosses the ‘border’ of the Feynman diagram?