# Violation of Newtons third Law and conservation of momentum

Three High energy Photons spontaneously convert into electron positron pairs, The electron on the left marked A is created and and destroyed within a short interval, sending an electric field burst towards electron B shortly after it's created, just enough so that Electrons B's electric field does not have enough time to reach and interact with electron A's, meaning that A exerts a force on B without B exerting a force on A

https://scontent-sjc.xx.fbcdn.net/hphotos-xpf1/v/t1.0-9/q85/s720x720/10945668_869527739755713_6251030958447359498_n.jpg?oh=5479ca362edb62068d30b9c6cf9d2704&oe=5587A156

atyy
Newton's third law does not hold even in classical electrodynamics. You are right that momentum conservation is a consequence of the third law in Newtonian physics. The correct generalization is to discard the third law and keep momentum conservation.

DrClaude
bhobba
Mentor
sending an electric field burst towards electron B shortly after it's created
In QED electric fields are not viewed that way - rather its described in terms of the field theory of electrons, the field theory of photons as the quanta of the em field, and their interaction which, if i remember correctly, is treated as a perturbation.

Beyond that I will have to leave it to those more conversant in QED - but what you wrote above is not a correct analysis.

Thanks
Bill

Your Feynman diagram (and, by extension, your thought experiment) is not physically possible, even though the basic observation about Newton's third law is accurate. A photon converting into an electron-positron pair is fine as an internal vertex, but such a process cannot conserve 4-momentum and so as a complete interaction has amplitude zero. You need a minimum of two photons to produce a free electron-positron pair. Similarly, an electron-positron pair cannot annihilate into a single photon. In both cases, you need a virtual electron to mediate the interaction.

Also, BTW, your arrows are not drawn correctly. One arrow flows into the vertex, the other flows out.

Your Feynman diagram (and, by extension, your thought experiment) is not physically possible, even though the basic observation about Newton's third law is accurate. A photon converting into an electron-positron pair is fine as an internal vertex, but such a process cannot conserve 4-momentum and so as a complete interaction has amplitude zero. You need a minimum of two photons to produce a free electron-positron pair. Similarly, an electron-positron pair cannot annihilate into a single photon. In both cases, you need a virtual electron to mediate the interaction.

Also, BTW, your arrows are not drawn correctly. One arrow flows into the vertex, the other flows out.
I see, thankyou