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Could you help me please, Im sure it is not even worthy of your attention, but anyway...

In Peskin, Schroeder - from expresion [tex] <0|\phi(x)\phi(y)|0> [/tex] survives [tex] <0|a_p a_q^\dag|0> [/tex] so it creates one-particle state |q> at position y and another one-particle state | p> at postion x. But how do I intuitively see that causuality/propagation of particle between these positions is imbeded and considered in that expresion?

And another question [tex] <0|\phi(x)|p>=.......e^ipx[/tex] formula 2.42

it's said that it is a position-space representation of the state |p> just as in NR QM <x|p>, so it should be projection of single-particle |p> state onto the <x| baisis and what vectors/basis that state is projected on? where is that <x| vectors in 2.42

P.S. Im sure i missed something very simple in understanding of above and that's why posting such "silly" questions

Thanks in advance

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# Simple question from Peskin Schroeder

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